Abstracts	
  of	
  INVITED	  SPEAKERS	
  	
  
of	
  Spintronics	
  with	  Antiferromagnets	
  workshop	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  

	
  
Spin	
  Currents	
  in	
  Antiferromagnets	
  

	
  
Axel	
  Hoffmann,1	
  Wei	  Zhang,1	
  Stephen	
  M.	
  Wu,1	
  Hilal	  Saglam,1,2	
  Joseph	  Sklenar,1,3	
  M.	
  Benjamin	  Jungfleisch,1,	
  Wanjun	  Jiang,1	
  Yaohua	
  Liu,1	
  John	
  E.	
  Pearson,1	
  Suzanne	
  G.	
  E.	
  te	
  Velthuis,1	
  J.	
  Samuel	
  Jiang,1	
  Anand	
  Bhattacharya,1	
  John	  B.	
  Ketterson,3	  Frank	
  Freimuth,4	
  Yuriy	
  Mokrousov,4	
  Amit	
  KC,5	
  Pavel	  Borisov,5	
  and	  David	
  Lederman,5	
  1Materials	
  Science	  Division,	
  Argonne	  National	
  Laboratory,	
  Argonne,	
  IL	
  60439,	
  USA	
  2Department	
  of	
  Physics,	
  Illinois	
  Institute	
  of	
  Technology,	
  Chicago,	
  IL	
  60616,	
  USA	
  3Department	
  of	
  Physics	
  and	  Astronomy,	  Northwestern	
  University,	
  Evanston,	
  IL	
  60208,	
  USA	
  4Peter	  Grünberg	
  Institut	
  and	
  Institute	
  for	  Advanced	
  Simulation,	
  Forschungszentrum	
  Jülich	
  and	
  JARA,	
  D-­‐52425	
  Jülich,	
  Germany	
  5Department	
  of	
  Physics	
  and	  Astronomy,	
  West	  Virginia	
  University,	  Morgantown,	
  WV	
  26506,	
  
USA	
  
	
  
Harnessing	
   spin	
   currents	
   is	
   one	   of	
   the	   promising	
   pathways	
   towards	
   low-­‐power	
   electronics	
  
[1].	
  	
  Towards	
  this	  end	  it	
  has	  recently	
  been	  recognized	
  that	  antiferromagnetic	
  materials	
  can	
  
play	
   a	
   more	
   active	   beyond	
   their	
   traditionally	
   established	
   role	   for	   providing	
   reference	  magnetization	
   direction	
   via	   exchange	
   bias.	
   	
   Namely,	
   it	
   has	   been	
   shown	
   both	
   theoretically	  and	
   experimentally	
   that	
   antiferromagnets	
   may	   be	   a	
   conduit	
   for	   spin	
   currents,	
   as	
   well	
   as,	
  actively	
   enable	
   spin	
   current	
   generation	
   and	   detection.	
   	
   With	   respect	
   to	
   the	   later	   aspect,	
   we	
  recently	
   demonstrated	
   spin	
   current	
   generation	
   both	   via	   spin	
   Hall	   effects	
   in	
   conducting	  antiferromagnets	
   and	   spin	
   Seebeck	
   effects	
   in	
   insulating	
   antiferromagnets.	
   	
   Using	
   CuAu-­‐I-­‐type	
   metallic	
   antiferromagnets	
   (PtMn,	
   IrMn,	
   PdMn,	
   and	   FeMn)	
   we	   showed	
   by	
   using	
   spin	
  pumping	
   that	   these	   alloys	
   have	
   significant	
   spin	
   Hall	   effects,	
   which	
   in	
   the	   case	   of	
   PtMn	  become	  comparable	
  to	
  the	
  ubiquitously	
  used	  Pt	
  [2].	
  	
  The	
  spin	
  Hall	  angles	  increase	
  for	  the	  alloys	   with	   heavier	
   element;	
   a	
   behavior	
   that	
   is	
   well	
   reproduced	
   by	
   first-­‐principle	  calculations	
   of	
   the	   spin	
   Hall	
   conductivities	
   based	
   on	
   intrinsic	
   spin	
   Hall	   effects.	
  	
  Furthermore,	
   the	   calculations	
   suggest	
   pronounced	
   anisotropies	
   of	
   the	   spin	
   Hall	  conductivities,	
   which	
   we	
   tested	
   using	
   spin	
   transfer	
   torque	
   ferromagnetic	
   resonance	  measurements	
   using	
   epitaxially	
   grown	
   antiferromagnetic	
   films	
   [3].	
   	
   We	
   observe	
   that	
  indeed	   the	   spin	
   Hall	
   conductivity	
   is	
   maximized	
   for	   different	
   growth	
   orientations	
   (a-­‐axis	
   for	  PtMn	
   and	   PdMn,	
   and	   c-­‐axis	
   for	   IrMn)	
   in	
   accordance	
   with	
   the	   first	
   principle	
   calculations.	
  	
  Lastly,	   using	
   epitaxial	
   MnF2/Pt	
   bilayers,	
   we	
   observe	
   spin	
   Seebeck	
   voltages	
   with	   distinct	
  features	
  due	  to	
  the	
  well-­‐known	
  spin-­‐flop	  transition	
  in	
  MnF2.	
  
Work	
  at	
  Argonne	
  was	
  supported	
  by	
  the	
  U.S.	
  DOE,	
  Office	
  of	
  Science,	
  Materials	
  Sciences	  and	
   Engineering	
   Division.	
   	
   Work	   at	
   Jülich	
   was	
   supported	
   by	
   SPP	
   1538	
   Programme	
   of	
   the	
  
DFG.	
  	
  Work	
  at	
  WVU	  was	
  supported	
  by	
  a	
  Research	
  Challenge	  Grant	
  from	  the	
  West	  Virginia	
  Higher	
   Education	
   Policy	
   Commission	
   (HEPC.DSR.12.29),	
   a	
   grant	
   from	
   the	   U.S.	
   NSF	
   (grant	
  No.	
  DMR-­‐1434897),	
  and	  the	
  WVU	
  Shared	
  Research	
  Facilities.	
  	
  References	
  
[1]	
  A.	
  Hoffmann	
  and	  S.	
  D.	
  Bader,	
  Phys.	
  Rev.	
  Appl.	
  4,	
  047001	
  (2015).	
  
[2]	
  W.	
  Zhang,	
  et	
  al.,	
  Phys.	
  Rev.	
  Lett.	
  113,	
  196602	
  (2014).	
  
[3]	
  W.	
  Zhang,	
  et	
  al.,	
  Phys.	
  Rev.	
  B	
  92,	  144405	
  (2015).	
  

[4]	
  S.	
  M.	
  Wu,	  et	
  al.,	
  arXiv:1509.00439.	
  

ANTIFERROMAGNETIC SKYRMIONSJOSEPH BARKER AND OLEG A. TRETIAKOV
Institute for Materials Research, Tohoku University,
Aoba-ku, Sendai 980-8577, Japan
Manipulating small spin textures, which can serve as bits of information, by electric current is
one of the main challenges in the field of spintronics. Ferromagnetic skyrmions recently attracted
a lot of attention because they are small in size and are better than domain walls at avoiding
pinning while moved by electric current. Meanwhile, ferromagnetic skyrmions still havedisadvantages such as the presence of stray fields and transverse dynamics, making them harder
to employ for spintronic applications. In this work, we propose a novel topological object: theantiferromagnetic (AFM) skyrmion. This topological texture has no stray fields and we show thatits dynamics are faster compared to its ferromagnetic analogue. We obtain the dependence of
AFM skyrmion radius on the strength of Dzyaloshinskii-Moriya interaction coming from
relativistic spin-orbit effects and temperature. We find that the thermal properties, e.g. such as the
AFM skyrmion radius and diffusion constant, are rather different from those for ferromagnetic
skyrmions. More importantly, we show that due to unusual topology the AFM skyrmions do nothave a velocity component transverse to the current and thus may be perfect candidates for
spintronic applications.

Antiferromagnetic spintronics
Tomas Jungwirth 1,2
12Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 162 00 Praha 6, Czech
Republic

School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom	  Louis	
   Néel	   pointed	
   out	   in	
   his	   Nobel	
   lecture	
   that	
   while	
   abundant	
   and	   interesting	
   from	
  theoretical	
  viewpoint,	
  antiferromagnets	
  did	  not	
  seem	  to	
  have	  any	
  applications.	
  Indeed,	
  the	  alternating	
   directions	
   of	
   magnetic	
   moments	
   on	
   individual	
   atoms	
   and	   the	   resulting	
   zero	
   net	  magnetization	
   make	
   antiferromagnets	
   hard	   to	
   control	
   by	
   tools	
   common	
   in	
   ferromagnets.	
  Strong	  coupling	
  would	
  be	
  achieved	
  if	
  the	
  externally	
  generated	
  field	
  had	  a	
  sign	  alternating	
  on	
  the	
  scale	  of	  a	
  lattice	
  constant	
  at	
  which	
  moments	
  alternate	
  in	
  AFMs.	
  However,	
  generating	
  
such	
   a	
   field	
   has	   been	
   regarded	
   unfeasible,	
   hindering	
   the	   research	
   and	
   applications	
   of	
   these	  abundant	
  magnetic	
  materials.	
  	
  
	
  
We	
   have	
   recently	
   predicted	
   [1]	
   that	
   relativistic	
   quantum	
   mechanics	
   may	   offer	
   staggered	
  current	
   induced	
   fields	
   with	
   the	   sign	
   alternating	
   within	
   the	   magnetic	
   unit	
   cell	   which	
   can	  facilitate	
  a	
  reversible	
  switching	
  of	
  an	
  antiferromagnet	
  by	
  applying	  electrical	
  currents	
  with	  comparable	
   efficiency	
   to	
   ferromagnets.	
   Among	
   suitable	
   materials	
   is	   a	   high	
   Néel	  temperature	
   antiferromagnet,	
   tetragonal-­‐phase	
   CuMnAs,	
   which	
   we	
   have	
   recently	
  synthesized	
   in	
   the	   form	
   of	
   single-­‐crystal	
   epilayers	
   structurally	
   compatible	
   with	   common	
  semiconductors	
   [2].	
   We	
   demonstrate	
   electrical	
   writing	
   and	   read-­‐out,	
   combined	
   with	
   the	  insensitivity	
   to	
   magnetic	
   field	
   perturbations,	
   in	   a	   proof-­‐of-­‐concept	
   antiferromagnetic	  memory	  device	
  [3].	
  	
  
	
  
[1]	
  	
  J.	
  Zelezny,	
  et	
  al.,	
  Phys.	
  Rev.	
  Lett.	
  113,	
  157201	
  (2014).	
  
[2]	
  P.	
  Wadley,	
  et	  al.,	
  Nat.	
  Commun.	
  4,	
  2322	  (2013).	
  
[3]	
  P.	
  Wadley	
  et	
  al.	  http://arxiv.org/abs/1503.03765	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  

	
  
TITLE:	
   Spinning of spins:	
  ferro- vs antiferromagnetic spintronics
SPEAKER:	
  Olena Gomonay
ABSTRACT:	
  Spintronics of antiferromagnets is a new emerging field which opens new perspectives

for the element base of information technologies. Practical application of AFM materials
however encounters the problems of deterministic switching (writing), measuring (reading) andstabilization (storage) of AFM state in the presence of spin current. This talk gives somefundamental principles of AFM magnetic dynamics and overviews our recent results on
manipulation the state of AFM nanoparticle by spin current. Starting from general principles wedemonstrate that spin current pumped into AFM particle induces nontrivial magnetic dynamics
and present simple analytical tool for its description. We also compare the peculiar features offerro-and antiferromagnetic dynamics for the typical spintronic materials and highlight the
problems of the predictable switching between different AFM states.	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  

Spin Hall Effects due to Critical Spin Fluctuationsin Spin Glass and Other Magnetic States

Sadamichi Maekawa
Advanced Science Research Center, Japan Atomic Energy Agency,
Tokai, Japan

Based on the skew scattering via collective spin fluctuations, it is proposed theoreticallythat the direct and inverse spin Hall effects (DSHE and ISHE) are unique tools to study
spin fluctuations in metals [1].
The theoretical results are applied to the recent experiments in a weak ferromagnetic
NiPd by Wei et al. [2] and a CuMnBi spin glass state by Niimi et al. [3].
[1] B Gu, T. Ziman and S. Maekawa; Phys. Rev. B86, 241303(R) (2012).
[2] D. H. Wei, Y. Niimi, B. Gu, T. Ziman, S. Maekawa and Y. Otani; Nature Commun.
3, 1058 (2012).
[3] Y. Niimi, M. Kimata, Y. Omori, B. Gu, T. Ziman, S. Maekawa, A. Fert and Y.
Otani; Phys. Rev. Lett. (Nov. 2, 2015).

	
  Interconnections	
  between	
  magnetic	
  state	  and	  transport	
  currents	  in	
  antiferromagnetic	
  Sr2IrO4	
  
	
  

M.	
  Tsoi	  Physics	
  Department,	
  University	
  of	
  Texas	
  at	
  Austin,	
  Austin,	
  Texas	
  78712,	
  USA	  	
  Interconnections	   between	
   magnetic	
   state	
   and	   transport	
   currents	
   in	
   ferromagnetic	   (F)	
  heterostructures	  are	  the	
  basis	  for	
  spintronic	
  applications,	
  e.g.	
  tunneling	
  magnetoresistance	
  and	
   spin-­‐transfer	
   torque	
   phenomena	
   provide	   a	
   means	
   to	
   read	   and	   write	
   information	
   in	  magnetic	
   memory	
   devices	
   like	
   STTRAM.	
   Similar	
   interconnections	
   were	   proposed	   [1]	
   to	  occur	
   in	
   systems	
   where	
   F-­‐components	
   are	   replaced	
   with	   antiferromagnets	
   (AFM).	
   We	  demonstrated	
  experimentally	
  the	
  existence	
  of	
  such	  interconnections	  in	
  antiferromagnetic	
  Mott	
   insulator	
   Sr2IrO4:	
   first,	
   we	
   found	
   [2]	
   a	
   very	
   large	
   anisotropic	
   magnetoresistance	  (AMR)	
   which	
   can	   be	
   used	   to	
   monitor	
   (read)	
   the	   magnetic	
   state	
   of	
   AFM;	
   second,	
   we	  demonstrated	
   [3]	
   the	   feasibility	
   of	
   reversible	
   resistive	   switching	
   driven	
   by	
   high-­‐density	
  currents/high	   electric	
   fields	
   which	
   can	   be	
   used	   for	   writing	
   in	
   AFM	   memory	   applications.	
  	
  These	  results	
  support	
  the	
  feasibility	
  of	
  AFM	
  spintronics	
  where	
  antiferromagnets	
  are	
  used	  in	
  place	  of	
  ferromagnets.	
  This	
  work	  was	
  supported	
  in	
  part	  by	  C-­‐SPIN,	
  one	  of	
  six	
  centers	
  of	
  STARnet,	
   a	
   Semiconductor	
   Research	
   Corporation	
   program,	
   sponsored	
   by	
   MARCO	
   and	  DARPA,	
  and	  by	
  NSF	
  grants	
  DMR-­‐1207577,	
  DMR-­‐1265162	
  and	  DMR-­‐1122603.	
  
	
  
[1]	
  A.	
  S.	
  Núñez	
  et	
  al.,	
  Phys.	
  Rev.	
  B	
  73,	  214426	
  (2006);	
  	
  
[2]	
  C.	
  Wang	
  et	
  al.,	
  Phys.	
  Rev.	
  X	
  4,	
  041034	
  (2014);	
  	
  
[3]	
  C.	
  Wang	
  et	
  al.,	
  arXiv1502.07982.	
  	
  

	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  

	
  
Spin-Transfer and Antiferromagnets
Allan MacDonald
The University of Texas at Austin, USAI will make some general remarks about antiferromagnets in spintronics and then talkabout current-induced torques including spin-orbit torques and the possible use of noncollinear antiferromagnetic states as spin-torque generators.

Propulsion of a domain wall by magnons in an antiferromagnet
Oleg Tchernyshyov
Johns Hopkins University, USA
Domain walls in magnetic nanowires can be used to store information and perform logicaloperations. Whereas the mechanism of domain wall propulsion in ferromagnet (by an appliedfield, spin-polarized current, or a flux of magnons) are well understood, much less is known
about the antiferromagnetic domain walls.
We analyze the dynamics of a domain wall in an easy-axis antiferromagnet driven by a current ofcircularly polarized magnons. Magnons pass through a stationary domain wall without reflection
and thus exert no force on it. However, they reverse their spin upon transmission, thereby
transferring two quanta of angular momentum to the domain wall and causing it to precess. A
precessing domain wall partially reflects magnons back to the source. The reflection of spinwaves creates a previously identified reactive force. We point out a second mechanism of
propulsion, which we term redshift: magnons passing through a precessing domain wall lower
their frequency by twice the angular velocity of the domain wall; the concomitant reduction ofmagnons' linear momentum indicates momentum transfer to the domain wall. We solve theequations of motion for spin waves in the background of a uniformly precessing domain wallwith the aid of supersymmetric quantum mechanics and compute the net force and torque applied
by magnons to the domain wall. Redshift is the dominant mechanism of propulsion at low spinwave intensities; reflection dominates at higher intensities. We derive a set of coupled algebraic
equations to determine the linear velocity and angular frequency of the domain wall in a steadystate.

Spin pumping and spin-transfer torques in antiferromagnet
Qian Niu
University of Texas, Austin, TX, USA
Spin pumping and spin-transfer torques are key elements of coupled dynamics of magnetization andconduction electron spin, which have been widely studied in various ferromagnetic materials. Recent
progress in spintronics suggests that a spin current can significantly affects the behavior of an
antiferromagnetic material [1], and the electron motion become adiabatic when the staggered field varies
sufficiently slowly [2]. However, pumping from antiferromagnets and its relation to current-induced torques
is yet unclear. In a recent study [3], we have solved this puzzle analytically by calculating how electrons
scatter off a normal metal-antiferromagnetic interface. The pumped spin and staggered spin currents arederived in terms of the staggered field, the magnetization, and their rates of change. We find that for bothcompensated and uncompensated interfaces, spin pumping is of a similar magnitude as in ferromagnets;
the direction of spin pumping is controlled by the polarization of the driving microwave. Via the Onsager
reciprocity relations, the current-induced torques are also derived, the salient feature of which isillustrated by a terahertz nano-oscillator.
[1] R. Cheng and Q. Niu, Phys. Rev. B \textbf{89}, 081105(R) (2014).
[2] R. Cheng and Q. Niu, Phys. Rev. B \textbf{86}, 245118 (2012).
[3] R. Cheng, J. Xiao, Q. Niu, and A. Brataas, Phys. Rev. Lett. \textbf{113}, 057601 (2014).

Optical control of antiferromagnetism
Takuya SatohKyushu University
All-optical magnetization switching has been studied extensively in recent years. A typical form of nonthermal magnetization control is the inverse Faraday effect. It involves rotation of the linear polarizationof a probe pulse induced by a circularly polarized pump pulse in a transparent medium. Spin precessionis also triggered with a linearly polarized pump pulse, in particular, a pulse polarized in a direction nonparallel to the crystal axes. This phenomenon is called the inverse Cotton-Mouton effect (ICME).
The interaction between light and magnetism is considered a promising route to the development ofenergy-efficient data storage technologies. To date, however, ultrafast optical magnetization control has
been limited to a binary process. Here, we report an arbitrary optical polarization state to be written
magnetically. The effect is demonstrated using a three-sublattice antiferromagnet hexagonal YMnO3.
Its three magnetic oscillation eigenmodes are selectively excited by the three polarization eigenstates ofthe light via the inverse magneto-optical effects. The magnetic oscillation state is then transferred backinto the polarization state of an optical probe pulse, thus completing an arbitrary optomagnonic writeread cycle [1].
[1] T. Satoh et al. Nature Photonics 9, 25 (2015).

Relativistic spin-orbit torques in anti-ferromagnets and related effects
Jairo Sinova
University of Mainz, Germany
Understanding the origin and properties of the different phases of materials and how tocontrol them is at the heart of condensed matter physics and physics in general. One of
the grand challenges of the field is to control spin-dependent properties without using
magnetic fields. To do so, one must resort to the relativistic nature of electrons, the spinorbit coupling (SOC), which connects the spin and charge of the electron. We havelearned how to exploit the relativistic SOC to create new paradigms of spin control incomplex materials. At the heart of these effects is the spin Hall effect and the inverse
spin-galvanic effect. Each of them have lead to new types of torques that generatemagnetization dynamics by different origins. The spin Hall effect generates a spincurrent that transfers its angular momentum via the spin transfer torque, whereas theother effect transfers orbital angular momenta from the lattice to the magnetization via
the SOC – a bit like a cat flipping itself. Transferring these questions to AFM we havepredicted a new Neel type spin-orbit torques (SOTs) which are able to electricallymanipulate the domain orientation of the Neel order parameter. This prediction has been
recently realized in CuMnAs experiments. We explore these new Need-SOTs in othersystems and study their relative strength. We also are extending some of their notions tomanipulation of spin-textures which may prove also useful in antiferromagnetic
spintronics.

	
  
	
  
	
  
Magnetism and transport in topological insulators	  Naoto	  Nagaosa1,2
1

RIKEN Center for Emergent Matter Science (CEMS)
Wako, Saitama 351-0198, Japan2
Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japannagaosa@riken.jp
Topological insulators (Tis) with magnetism offer many interesting opportunity from the viewpoint of
spintronics. Especially, their surface states show the spin-momentum locking, i.e., the strong coupling
limit of the spin-orbit interaction. In this talk, I will discuss the quantum Hall effect (QHE) and thequantized anomalous Hall effect (QAHE) of TIs. The novel \nu=0 state is the issue in the former system,
while the focus is on the spin textures such as domain wall and skyrmions in the latter system.
Collaborators of these works are R. Wakatsuki, M. Ezawa, T.Morimoto, and A. Furusaki.
[1] “Charge and spin transport in edge channels of a $ν=0$ quantum Hall system on the surface of
topological insulators”, Takahiro Morimoto, Akira Furusaki, Naoto Nagaosa,Phys. Rev. Lett. 114, 146803 (2015).
[2] “Topological magnetoelectric effects in thin films of topological insulators“,
Takahiro Morimoto, Akira Furusaki, Naoto Nagaosa, Phys. Rev. B92, 085113 (2015)[3] “Domain wall of a ferromagnet on a three-dimensional topological insulator”,
Ryohei Wakatsuki, Motohiko Ezawa, Naoto Nagaosa, Scientific Reports 5, 13638 (2015).

	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  

Thermal vector potential theory of transport induced by temperature
gradient
Gen Tatara
RIKEN Center for Emergent Matter Science (CEMS)
A microscopic formalism to calculate thermal transport coefficients was presented by Luttinger [1] in 1964. He
introduced a fictitious scalar field called a ‘gravitational’ potential, Ψ, which couples to the local energy density,
E, by an interaction Hamiltonian∫
HL = d3 rΨE.
(1)
It was argued that Ψ satisfies ∇Ψ = ∇T
T and that thermal transport coefficients are calculated based on linear
response theory (Kubo formula) taking account of the interaction HL . Many works have been carried out based on
the Luttinger’s formalism. It turned out that naive application of Kubo formula may result in wrong thermal coefficients diverging at zero temperature, and the divergence was argued to be due to a wrong treatment of equilibrium
contribution [2].
In this talk, we present a description of thermal effects by using a thermal vector potential AT , which couples
to the energy current density jE via∫
HAT ≡ − d3 rjE · AT
(2)
and satisfies∂t AT =

∇T
.
T

(3)

The vector potential formalism [3] is free from unphysical divergences in Luttinger’s formalism, because theequilibrium (‘diamagnetic’) currents are treated consistently. The mathematical structure for thermal transportcoefficients are shown to be identical with the electric ones if the electric charge is replaced by energy. The results
indicates that the thermal vector potential couples to energy current via the minimal coupling: In the case of freeelectron with mass m and energy ϵk (k is the wave vector) the interaction reads (including electromagnetic vector
potential A)
H=

~2 ∑
2
(k − eA − ϵk−eA AT ) .
2m

(4)

k

Thermal vector potential thus acts as a gauge field coupling to the energy instead of the charge e. The formalism
is applied to thermally-induced dynamics of magnetization structures [4].

References[1] J. M. Luttinger, Phys. Rev. 135, A1505 (1964).
[2] T. Qin, Q. Niu, and J. Shi, Phys. Rev. Lett. 107, 236601 (2011).
[3] G, Tatara, Phys. Rev. Lett. 114, 196601 (2015).
[4] G. Tatara, Phys. Rev. B 92, 064405 (2015).

	
  
	
  
	
  
Anti-damping spin transfer torque through antiferromagnet
Takahiro Moriyama
Kyoto University, Institute for Chemical Research, Kyoto 611-0011, Japan.
Spin transfer torque (STT) has been an efficient and promising technique to control
magnetizations of ferromagnetic materials in modern spintronic devices. This novel technique isbased on an interaction between electron spin and local magnetic moments. The same interaction
should be conserved in antiferromagnets (AFMs), in which there are microscopic local magnetic
moments that compensate each other to exhibit no net magnetization.
In this work, we prepared MgO(001) substrate/Pt 5nm/NiO 10nm/FeNi 3nm/SiO2 5nm
multilayers, in which the films are epitaxially grown until the NiO layer, and performed a spin
torque ferromagnetic resonance (ST-FMR) measurement to quantify the anti-damping spin
torque transported between the Pt and the FeNi through the antiferromagnetic NiO layer. A purespin current is created by the spin Hall effect of the Pt and injected into the NiO. The schematic
layer structure of the injection scheme is shown in Fig. 1(a). As shown in Fig. 1(b), it is foundthat the FMR linewidth monotonously varies with the d.c. current flowing in the structure.	
  As the
ST-FMR measurement is only sensitive to the linewidth (i.e. damping) of the FeNi layer, thischange in the linewidth in Pt/NiO/FeNi can be interpreted in a way that the spin current istransferred through the NiO and interacts with the FeNi. This intriguing spin current transport
can be explained by the angular momentum transfer mediated by the antiferromagnetic magnons[1,2]. Our results assure that the spin current exerts a torque on the NiO magnetic moments andexcites their dynamics. In the talk, recent results will be also discussed.

Figure 1 (a) Schematic illustration of the sample structure. (b) FMR linewidth change as afunction of the d.c. current flowing in the sample.
[1] Moriyama, et al., APL 106, 162406 (2015) [2] Takei et al., PRB (R) 92, 020409 (2015)

	
  
	
  
	
  

Ultrafast	
  pulses,	
  spin	
  torque	  and	
  artificial	
  antiferromagnets
Dr Xavier Waintal
INAC CEA Grenoble, France
Artificial antiferromagnets (Ferromagnetic-Normal-Ferromagnetic spin valves
Antiferromagnetically coupled by the interlayer exchange interaction) can be viewed as
the spintronics version of the Fabry-Perot interferometer. In this talk, I will introduce the conceptof dynamical control of interference pattern with ultra fast voltage pulses.
I will show that this idea can be used on artificial antiferromagnets to control the magnetic exchangeinteraction leading to a new sort of (dynamical) spin torque. In a second part,I will discuss the magnetic response of theseartificial antiferromagnets to spin torque, that naturally leads
to spin torque oscillator (STO) behavior even in the absence of external fields.

Collective spin transport through antiferromagnets
Yaroslav Tserkovnyak, Se Kwon Kim, and So Takei
Department of Physics and Astronomy, University of California, Los Angeles, California
90095, USA
Antiferromagnetic insulators are a promising medium for low-dissipation transmission ofspin currents. In the absence of charge carriers, the spin is transmitted collectively,
either by thermal cloud of magnons or by a coherent precessional dynamics of the Néelorder. The latter can be understood as an instance of spin superfluidity, which isoperative even at absolute zero temperature. In this talk, I will discuss two experimental
geometries where such spin currents can be probed: (1) Easy-plane antiferromagnet
contacted by heavy metals for injecting (detecting) spin currents by the direct (inverse)
spin Hall effect. In such systems, the spin superfluidity can be manifested as a longranged (electric) transconductance in the metals. (2) Easy-axis antiferromagnet
sandwiched between a heavy metal and ferromagnetic insulator. The spin Hall effect atthemetal/antiferromagnet
interfaceandexchange
couplingatthe
antiferromagnet/ferromagnet interface allow for the spin currents (carried by bothcoherent dynamics and thermal magnons) to be transmitted across the trilayer. Thisestablishes reciprocal coupling between charge currents in the metal with magnetic
dynamics in the ferromagnet, which can be readily accessed with the state-of-the-art
experimental tools. Finally, I will discuss how thermally-activated topological transport ofchiral domain walls recovers superfluid spin hydrodynamics in the presence of parasitic
anisotropies.	
  Facet-dependent giant spin orbit torque in single
crystalline antiferromagnetic Ir-Mn / ferromagnetic
permalloy bilayers
Stuart S. P. Parkin1,2§	  ,	
  Weifeng Zhang1, Wei Han1, and See-hun Yang1
1

IBM Almaden Research Center, San Jose, California 95120, USA

2

Max Planck Institute for Microstructure Physics, Halle (Saale) D-06120, Germany§

email: stuart.parkin@mpi-halle.mpg.deThere has been considerable interest in spin-orbit torques for the purpose of manipulating
the magnetization of ferromagnetic (FM) films or nano-elements for spintronic
technologies. Spin orbit torques are derived from spin currents created from charge
currents in materials with significant spin orbit coupling that diffuse into an adjacent FMmaterial. There have been intensive efforts to search for candidate materials that exhibit
large spin Hall angles, i.e. efficient charge to spin current conversion. Here we report,effusing spin torque ferromagnetic resonance, the observation of a giant spin Hall angle θ SHofup to ~0.35 in (100) oriented single crystalline antiferromagnetic IrMn3 thin films, coupledeff
to ferromagnetic permalloy layers, and a θ SH	
  that is about three times smaller in (111)efforiented films. Two distinct mechanisms are identified that contribute to θ SH
: a first

mechanism, which is facet independent, that arises from conventional bulk spin-dependent
scattering within the IrMn3 layer; and a second novel mechanism that derives from the
IrMn3 antiferromagnetic structure itself. By manipulating the populations of the various
eff
AF domains we show that θ SH
can be dramatically enhanced for (100) oriented IrMn3

films.
	  Spin	
  Currents	
  in	
  Antiferromagnets	
  and	
  Ferrimagnets	
  	
  
	
  
M.	
  Kläui1,2	
  1Institute	
  of	
  Physics,	
  Johannes	
  Gutenberg-­‐University	
  Mainz,	
  Staudingerweg	
  7,	
  55128	
  Mainz,	  Germany	  2Graduate	
  School	
  of	
  Excellence	  Materials	
  Science	
  in	
  Mainz	
  (MAINZ),	
  Staudinger	
  Weg	  9,	  55128	
  Mainz,	  Germany	  	  Antiferromagnetic	
   materials	
   were	
   discovered	   a	
   long	
   time	
   ago,	   but	   due	   to	
   their	
   zero	
   net	  magnetization	
   they	   have	
   been	
   considered	
   for	
   a	
   long	
   time	
   not	   to	
   be	
   useful.	
   Furthermore	
   the	  manipulation	
   using	
   conventional	
   magnetic	
   fields	
   is	
   challenging.	
   However	   recently,	
   these	  materials	
   have	
   received	
   renewed	
   attention	
   due	   to	   possible	
   manipulation	
   based	
   on	
   new	  approaches	
  such	  as	
  photons	
  [1],	
  spin-­‐orbit	
  torques	
  [2]	
  and	  thermal	
  spin	
  currents	
  [3].	
  We	
  firstly	
  study	
  the	
  spin	  Seebeck	
  effect	  (SSE)	
  that	  has	
  opened	
  a	
  new	
  avenue	
  to	
  generating	  spin	
   currents	
   in	
   insulators	
   by	
   exploiting	   a	
   temperature	
   gradient	
   [4].	
   While	
   in	
   ferromagnets	
  the	
   origin	
   has	   been	
   identified	
   as	
   bulk	
   magnonic	
   spin	
   currents	
   [5],	
   the	   situation	
   is	
   more	
  complex	
   in	
   ferrimagnets	
   and	   antiferromagnets	
   with	
   a	
   complex	
   interplay	
   of	   different	
   sub-­‐lattices	
  comprising	
  different	
  atom	  species.	
  We	
  study	  Gadolinium	
  Iron	
  Garnet	
  (GIG),	
  where	  at	
  high	  temperatures,	
  the	  d	
  site	  Fe	
  ions	  dominate	
  the	  net	
  magnetization	
  of	
  GIG	
  and	  as	
  the	
  temperature	
   is	
   reduced,	
   the	   magnetization	
   of	
   the	   Gd	
   sub-­‐lattice	
   strongly	
   increases,	
   and	  together	
   with	
   the	   Fe	
   magnetization	
   at	
   the	   a	
   site	   eventually	
   overwhelms	
   the	   Fe	  magnetization	
  at	
  the	  d	
  site,	  resulting	  in	
  so-­‐called	
  magnetic	
  compensation	
  temperature	
  [6].	
  When	
   measuring	
   the	   SSE	   measurements	
   of	
   GIG	   films,	
   two	   sign	
   changes	
   of	
   SSE	
   signal	
   are	  observed	
  with	  decreasing	
  temperature:	
  The	
  first	  sign	
  change	
  at	
  a	
  temperature	
  close	  to	
  the	
  compensation	
   temperature	
   where	
   the	   signal	
   changes	
   sign	   abruptly	
   with	   unaltered	
  amplitude,	
  indicating	
  that	  the	  majority	
  of	
  the	
  spin	
  current	
  is	
  mainly	
  caused	
  by	
  the	  Fe	  sub-­‐
lattices,	
  which	  reorient	
  their	
  direction	
  at	
  this	  temperature.	
  A	
  second	
  sign	
  change	
  appears	
  more	
   gradually	
   at	
   low	
   temperatures	
   and	   it	
   can	   be	
   attributed	
   to	
   an	
   interplay	
   of	
   i)	
   the	  temperature	
   dependent	
   ordering	
   of	
   the	   Gd	
   and	   Fe	
   sub-­‐lattices	
   leading	   to	   a	   change	
   in	
   the	  magnon	  dispersion	
  and	
  occupation	  and	
  ii)	  the	
  temperature	
  dependence	
  of	
  the	
  spin-­‐mixing	  conductances	
   of	
   the	   different	
   sub-­‐lattices	
   [6].	
   We	
   furthermore	
   study	
   the	   SSE	
   also	
   in	  antiferromagnets,	
  such	  as	
  LaMnO3	
  and	
  Sr2IrO4	
  and	
  find	  signatures	
  of	
  the	
  SSE.	
  Finally	
   we	
   study	
   spin	
   orbit	
   torques	
   in	
   the	   antiferromagnet	
   Mn2Au	
   where	
   large	
   effects	
   have	  been	
  predicted	
  [2].	
  We	
  establish	
  the	
  growth	
  of	
  the	
  material	
  and	
  characterize	
  its	
  magnetic	  properties	
  [7]	  as	
  well	  as	
  the	
  effects	
  of	
  current	
  injection.	
  	
  
	
  
References	
  
[1]	
  A.	
  Kimel	  et	
  al.,	
  Nature	
  429,	
  850	  (2004)	
  
[2]	
  J.	
  Zelezny	
  et	
  al.,	
  Phys.	
  Rev.	
  Lett.	
  113,	
  157201	
  (2014)	
  
[3]	
  S.	
  Seki	
  et	
  al.	
  arXiv	
  cond-­‐mat.str-­‐el/1508.02555	
  (2015);	
  S.	
  Wu	
  et	
  al.	
  arXiv	
  cond-­‐mat.mtrl-­‐
sci/1509.00439	
  (2015)	
  	
  
[4]	
  K.	
  Uchida	
  et	
  al.,	
  Nat.	
  Mater.	
  9,	
  894	  (2010).	
  
[5]	
  A.	
  Kehlberger	
  et	
  al.,	
  Phys.	
  Rev.	
  Lett.	
  115,	
  096602	
  (2015)	
  	
  

[6]	
  S.	
  Geprägs,	
  et	
  al.,	
  arXiv:1405.4971	
  
[7]	
  M.	
  Jourdan	
  et	
  al.,	
  J.	
  Phys.	
  D:	
  Appl.	
  Phys.	
  48,	
  385001	
  (2015)	
  Electric probe for spin transition and fluctuation
Dazhi	
  Hou	  	  
	  WPI-­‐AIMR,	
  Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 Japan	
  
	
  
Spin	
   fluctuation	
   and	   transition	
   have	
   always	
   been	
   one	   of	
   central	
   topics	
   of	
   magnetism	   and	  condense	
  matter	  science.	
  In	
  this	  talk	  I	
  would	
  like	  to	
  introduce	
  our	  recent	
  progress	
  that	  spin	
  pumping,	
  frequently	
  used	  in	
  nanoscale	
  spintronic	
  devices,	
  provides	
  a	
  desktop	
  micro	
  probe	  for	
  spin	
  fluctuation	  and	  transition;	
  not	
  only	  a	
  neutron	
  beam,	
  spin	
  current	
  is	
  also	  a	
  flux	
  of	
  
spin	
  without	
  an	
  electric	
  charge	
  and	
  its	  transport	
  reflects	
  spin	
  fluctuation	
  in	
  a	
  sample.	
  We	
  demonstrate	
   detection	
   of	
   anti-­‐ferromagnetic	
   transition	
   in	
   ultra-­‐thin	
   CoO	   films	
   via	  frequency	
   dependent	
   spin-­‐current	
   transmission	
   measurements.	
   This	   method	
   allows	
   us	
   to	
  access	  spin	  realm	
  in	
  an	
  electric	
  manner	
  in	
  minute	
  devices	
  which	  are	
  necessary	
  in	
  today's	
  electronics	
  and	
  spintronics.	
  
	
  
	
  

	
  

	
  

	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  
	
  

Poster	  Abstracts	
  	
  
	
  

of	
  Spintronics	
  with	  Antiferromagnets	
  workshop	
  Macrospin Dynamics in Antiferromagnets Triggered by Sub-20 femtosecond
Injection of Nanomagnons
D. Bossini, S. Dal Conte, Y. Hashimoto, A. Secchi, R. Pisarev, Th. Rasing, G.
Cerullo and A.V. Kimel
The understanding of how the sub-nanoscale exchange interaction evolves inmacroscale correlations and ordered phases of matter, such as magnetismand superconductivity, requires to bridge the quantum and classical worlds.
This monumental challenge has so far only been achieved for systems close
to their thermodynamical equilibrium. Here we follow in real time the ultrafast
dynamics of the macroscale magnetic order parameter triggered by theimpulsive optical generation of spin excitations with the shortest possible
nanometer-wavelength and femtosecond-period. Our experiments
demonstrate even the coherent manipulation of the phase and amplitude ofthese femtosecond nanomagnons, whose frequencies are defined by theexchange energy. These findings open up novel opportunities for
fundamental research on the role of short-wavelength spin excitations inmagnetism and strongly correlated material; they also suggest thatnanospintronics and nanomagnonics can employ coherently-controllable
spin waves with frequencies in the 20 THz domain.

Magnetization dynamics in trilayer synthetic antiferromagnets
Takahiro Chiba1, Gerrit E. W. Bauer1,2,3, and Saburo Takahashi1
1

Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
2
WPI-AIMR, Tohoku University, Sendai, Miyagi 980-8577, Japan
3
Kavli Institute of NanoScience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands

Recently, a new direction in spintronics has been emerging in which antiferromagnets(AFMs) take the role of ferromagnet (FMs) as active elements of memory or logic devices [1],e.g. because AFMs do not generate stray fields themselves. On the other hand, drawbacks are
the difficulty to control AFMs by magnetic fields and much higher resonant frequencies (THz),which make difficult to match with conventional electronic circuits.
Motivated by experimental results that hitherto have been unexplained [2], we focus on thetheory of the simplest of synthetic antiferromagnets, i.e. the antiferromagneticallyexchange-coupled spin valve. These devices have the features of natural AFMs but with easily
accessible resonant frequencies that are tunable by weak magnetic fields. By rigorous model
calculations, we study the magnetic damping of synthetic AFMs as affected by mutual
pumping of spin currents and spin transfer torques or “dynamic exchange interaction” [3]. We
formulate the dynamic exchange of spin currents in anoncollinear texture based on the spin diffusion modelwith quantum mechanical boundary conditions at theinterfaces and derive the Landau-Lifshitz-Gilbertequations coupled via the static interlayer non-local andthe dynamic exchange interactions. We also obtain
analytic expressions for the linewidths of magnetic
resonant modes (acoustic and optical) for
magnetizations canted by applied magnetic fields. We
find that noncollinear magnetizations induce anadditional damping and that FMR linewidths strongly
depend on the type of the resonant modes as well as thestrength of magnetic fields. Our calculated resultscompare favorably with experiments [4] as shown in
Fig. 1. We also investigate a resonant frequency
modulation in both modes via spin Hall effect. Ourmodel calculation paves the way for the theoreticaldesign of synthetic AFM material with an application Fig.1: (a) Derivative of the microwave abpotentialfordata-storage
technologies
in sorption spectrum [5] (b) Computed linewidths of the acoustic (A) and optical (O)antiferromagnetic spintronics.
modes [2].

References[1] R. Duine, Nat Mater. 10, 344 (2011); A. H. MacDonald and M. Tsoi, Phil. Trans. Royal
Soc. A 369, 3098 (2011).
[2] K. Tanaka, T. Moriyama, M. Nagata, T. Seki, K. Takanashi, S. Takahashi, and T. Ono,
Appl. Phys. Express 7, 063010 (2014).
[3] B. Heinrich, Y. Tserkovnyak, G. Wolterdorf, A. Brataas, R. Urban, and G. E. W. Bauer,
Phys. Rev. Lett. 90, 187601 (2003).
[4] T. Chiba, G. E. W. Bauer, and S. Takahashi, Phys. Rev. B 92, 054407 (2015).
[5] Z. Zhang, L. Zhou, P. E. Wigen, and K. Ounadjela, Phys. Rev. Lett. 73, 336 (1994).

Anisotropic magnetoresistance of antiferromagnetic MnTe
D. KRIEGNER1, H. REICHLOVA2, K. OLEJNIK2, K. VYBORNY2, V. NOVAK2, X.
MARTI2, V. HOLY1, V. V. VOLOBUEV3,4, G. SPRINGHOLZ3, T. JUNGWIRTH2,5
1
Department of Condensed Matter Physics, Charles University in Prague,
Ke Karlovu 5, 121 16 Praha 2, Czech Republic, dominik.kriegner@gmail.com
2
Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6, Czech Republic
3
Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz,
Altenbergerstr. 69, 4040 Linz, Austria
4
National Technical University "Kharkiv Polytechnic Institute", 61002 Kharkiv, Ukraine
5
School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom

Recent studies have demonstrated the potential of metallic antiferromagnets as the active
component in spintronic devices. In addition to their static role as pinning layers in harddisk read heads and magnetic memories they were shown to exhibit memory behavior
when cooled in different field directions [1] and are even electrically switchable [2] due tocurrent induced torques [3]. In order to move the research on antiferromagnetic spintronics
one step further, new antiferromagnetic materials need to be explored with respect to theirelectronic and magnetotransport properties. Especially appealing are antiferromagnetic
semiconductors which allow the combination of spintronic and semiconductormicroelectronic functionalities in one and the same material.
In this work we present magnetotransport investigations of hexagonal MnTe epitaxial thinfilms. MnTe is an antiferromagnet with the Neel temperature of 310 K and exhibits
semiconducting properties with an optical gap of ~1.3 eV [4] and the possibility of tuning
the carrier concentration by doping [5]. We use MnTe thin films grown epitaxially on
InP (111)A substrates by molecular beam epitaxy from which we produce Hall bar
structures by e-beam lithography and wet etching. We observe the development of two
distinct resistance states when we cool our structures from above the transition temperaturein an applied magnetic field. Once these states are set, they cannot be switched at low
temperature by magnetic fields up to our largest experimentally available field of 2 T.
During heating the states remain distinct until the transition temperature. By performing
field cooling with magnetic field in different directions we study the symmetry of thiseffect. We find a sine-square behavior as regularly observed in ferromagnets and expected
for an effect quadratic in the magnetic field. The amplitude of the effect is >1% at low
temperature, but remains detectable up to the transition temperature close to 300K.
References[1] X. Marti, I. Fina, C. Frontera, Jian Liu, P. Wadley, Q. He, R. J. Paull, J. D. Clarkson, J. Kudrnovský, I.
Turek, J. Kuneš, D. Yi, J-H. Chu, C. T. Nelson, L. You, E. Arenholz, S. Salahuddin, J. Fontcuberta, T.
Jungwirth, R. Ramesh, Nature Materials 13, 367–374 (2014)[2] P. Wadley, B. Howells, J. Zelezny, C. Andrews, V. Hills, R. P. Campion, V. Novak, F. Freimuth,
Y. Mokrousov, A. W. Rushforth, K. W. Edmonds, B. L. Gallagher, T. Jungwirth,
http://arxiv.org/abs/1503.03765[3] J. Železný, H. Gao, K. Výborný, J. Zemen, J. Mašek, Aurélien Manchon, J. Wunderlich, Jairo Sinova, and
T. Jungwirth, Phys. Rev. Lett. 113, 157201 (2014)[4] O. Madelung, U. Rössler, M. Schulz, SpringerMaterials, Springer-Verlag GmbH, Heidelberg, (2000)
DOI: 10.1007/10681735_478[5] J. D. Wasscher, PhD thesis, Technische Hogeschool Eindhoven, (1969) DOI: 10.6100/IR43336

Two-Fluid Theory for Spin Superfluidity in Magnetic Insulators(B. Flebus, S. A. Bender, Y. Tserkovnyak and R. A. Duine)

We investigate coupled spin and heat transport in easy-planemagnetic insulators. These materials display a continuous phasetransition between normal and condensate states that is controlled by
an external magnetic field.
Using hydrodynamic equations supplemented by Gross-Pitaevski
phenomenology and magnetoelectric circuit theory, we derive a twofluid model to describe the dynamics of thermal and condensed
magnons, and the appropriate boundary conditions in a hybrid
normal-metal|magnetic-insulator|normal-metal heterostructure.
We discuss how the emergent spin superfluidity canexperimentally probed via a spin Seebeck effect measurement.
	
  

be

Phenomenology of antiferromagnetic dynamics
Hristo Velkov and Jairo Sinova

Abstract
Ferromagnets are the established components of current electronic andspintronic devices. Recently, however, a lot of effort has been put into
investigating an alternative platform for spintronics - antiferromagnetic
materials. Much faster magnetization dynamics and abundance in nature area few characteristics that makes them stand out compared to theferromagnets.
In this work we study collinear antiferromagnets which consist of twomagnetic sublattices and develop the phenomenological theory in thepresence of an external magnetic field and the Dzyaloshinskii-Moriya
interaction. We derive the LLG equations for the Nèel order parameter andapply the theory to investigate the magnetization dynamics of rigid magnetic
textures.	
  Spin-Orbit effects in Exotic 2-D Anti-Ferromagnetic Materials
with Non-Collinear Spin
J. Gayles,1, 2 S. Hemmatiyan,1, 2 S.C. Wu,3 Y. Yamane,1 B.Yan,3, 4 Y.
Mokrousov,5 and J. Sinova1, 2, 6
1

Institut fu ̈r Physik, Johannes Gutenberg Universita ̈t Mainz, D-55099 Mainz,
Germany 2Department of Physics & Astronomy, Texas A&M University, College
Station, Texas 77843-4242, USA 3Max Planck Institute for Chemical Physics of Solids,
D-01187 Dresden, Germany4Max Planck Institute for Physics of Complex Systems, D01187 Dresden, Germany5Peter Gru ̈nberg Institut & Institute for Advanced
Simulation,Forschungszentrum Ju ̈lich and JARA, 52425 Ju ̈lich, Germany6Instituteof Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6 Czech Republic
We calculate first spin-orbit effects in exotic two-dimensional materials governed byberry-phase physics using first principle calculations. We see anti-ferromagnetic
state in half passivated graphene and stanene with Fluorine and Chlorine
respectively. These systems show sizable DMI that is less than the exchangeinteraction and would cause long wavelength spin-spirals to be the ground state. We
show the type of magnetism and the strength of the spin-orbit effects is controlled by
the passivated ion. Additionally, these systems display Heisenberg exchange and insome case superexchange where we show how spin-orbit physics plays a role insimple band structures. Furthermore graphene like systems have attracted muchattention for magnetic devices. Furthermore we perform ”coarse grain” calculations
to understand the dynamics of these systems in the presence of external fields.

Spin	
  caloric	
  transport	
  in	
  compensated	
  ferrimagnets	
  Joel	
  Cramer1,	
  S.	
  Geprägs2,	
  A.	
  Kehlberger1,	
  E.-­‐J.	
  Guo3,	
  R.	
  Gross2,	
  S.T.B.	
  Goennenwein2,	
  	
  and	  M.	
  Kläui1	
  1

Institute	
  of	
  Physics,	
  Johannes	
  Gutenberg-­‐University	
  Mainz,	
  Staudingerweg	
  7,	
  55128	
  Mainz,	  Germany	  2Walther-­‐Meißner-­‐Institut,	
  Bayerische	
  Akademie	
  der	
  Wissenschaften,	  85748	
  Garching,	
  Germany	  3Quantum	
  Condensed	
  Materials	
  Division,	
  Oak	
  Ridge	
  National	
  Laboratory,	
  37830,	
  Oak	
  Ridge,	
  TN,	
  USA	  
	  In	  recent	
  years,	
  it	
  has	  been	
  shown	
  that	  the	
  application	
  of	
  temperature	
  gradients	
  allows	
  for	  the	
   generation	
   of	
   spin	
   currents	
   in	
   various	
   ferromagnetic	
   materials.	
   Referring	
   to	
   its	   thermo	
  electrical	
   equivalent,	
   this	   phenomenon	
   is	
   called	
   spin	
   Seebeck	
   effect	   (SSE)	
   [1].	
   In	
   case	   of	  insulators,	
  spin	
  currents	
  are	
  carried	
  by	
  spin	
  waves	  (magnons)	
  with	  finite	
  propagation	
  length	
  moving	  from	  the	
  hot	  to	
  the	  cold	  end	  of	
  the	
  solid	
  [2].	
  In	
  adjacent	
  heavy	  metal	
  layers	
  these	  spin	
   currents	
   are	   converted	
   into	
   detectable	
   charge	
   currents	
   due	   to	
   the	   inverse	
   spin	
   Hall	
  effect	  (ISHE)	
  [3].	
  The	
  occurrence	
  of	
  the	
  SSE	
  has	  been	  investigated	
  in	
  Gadolinium	
  Iron	
  Garnet	
  (GIG)/Platinum	
  (Pt)	
   hybrids	
   [4].	
   GIG	   is	   a	   ferrimagnetic	
   insulator	
   which	
   comprises	
   antiferromagnetically	
  coupled	
   Fe	
   and	   Gd/Fe	
   sublattices	
   with	   different	
   temperature	
   dependences,	
   exhibiting	   a	
  magnetic	
   compensation	
   point	
   Tcomp.	
   By	
   probing	
   the	   spin	
   Seebeck	
   voltage	
   as	   a	   function	
   of	
  temperature	
   two	   sign	
   changes	
   of	
   the	   signal	
   appear	
   (Fig.	
   1).	
   This	   observation	
   and	   the	   fact	
  that	
  the	
  signal	
  does	  not	
  follow	
  the	
  trend	
  of	
  the	
  sample’s	
  net	
  magnetization	
  point	
  towards	
  a	
  complex	
   interplay	
   of	
   the	   involved	
   sublattice.	
   In	
   addition	
   to	
   that,	
   as	
   the	   observation	
   of	
   the	
  
SSE	
  in	
  antiferromagnetic	
  insulators	
  has	  recently	
  been	
  shown	
  by	
  [5,	  6]	  preliminary	  results	
  on	
  similar	
  systems	
  will	  be	
  presented.	
  
	
  

	
  

Fig.	
  1	
  Temperature	
  dependence	
  of	
  net	
  magnetization	
  M	
  and	  the	
  spin	  Seebeck	
  signal	
  ISSE.	
  M	
  shows	
  a	
  minimum	  near	
  the	
  compensation	
  point	
  Tcomp	
  while	  ISSE	  reveals	
  two	
  sign	
  changes.	
  Taken	
  and	  modified	
  from	  [4].	
  

	
  
[1]	
  Uchida	
  et	
  al.	  Nature	
  455,	
  778	  (2008)	
  [2]	
  Kehlberger	
  et	
  al.	
  Phys.	
  Rev.	
  Lett.	
  115,	
  096602	
  (2015)	
  [3]	
  Saitoh	  et	  al.	  Appl.	
  Phys.	
  Lett.	
  88,	
  182509	
  (2006)	
  [4]	
  Geprägs	
  et	
  al.	
  arXiv	
  cond-­‐mat.mes-­‐hall/1405.4971	
  (2014)	
  [5]	
  Seki	
  et	
  al.	
  arXiv	
  cond-­‐mat.str-­‐el/1508.02555	
  (2015)	
  
[6]	
  Wu	
  et	
  al.	
  arXiv	
  cond-­‐mat.mtrl-­‐sci/1509.00439	
  (2015)	
  Enhanced spin pumping by antiferromagnetic IrMn thin films around themagnetic phase transition
L. Frangou,1,2,3 S. Oyarzun,4,5 S. Auffret,1,2,3 L. Vila,4,5 S. Gambarelli,6,7 and V. Baltz1,2,3
1	
  Univ.	
  Grenoble	
  Alpes,	
  SPINTEC,	
  F-­‐38000	
  Grenoble,	
  France	  	
  CNRS,	  SPINTEC,	
  F-­‐38000	
  Grenoble,	
  France	  3
	
  CEA,	
  INAC-­‐SPINTEC,	
  F-­‐38000	
  Grenoble,	
  France	
  4
	
  Univ.	
  Grenoble	
  Alpes,	
  NM,	
  F-­‐38000	
  Grenoble,	
  France	  5
	
  CEA,	
  INAC-­‐NM,	
  F-­‐38000	
  Grenoble,	
  France	  6	
  Univ.	
  Grenoble	
  Alpes,	
  SCIB,	
  F-­‐38000	
  Grenoble,	
  France	  7
	  CEA,	
  INAC-­‐SCIB,	
  F-­‐38000	
  Grenoble,	
  France	  2

We report experimental measurements of a spin pumping effect owing to fluctuating IrMn
thin films [1]. Spin injection by a precessing NiFe ferromagnet into IrMn spin sinks is used.
Enhanced damping is observed around the IrMn magnetic phase transition [2], [3]. Our data
are corroborated by a recent theory [4] and converted into interfacial spin mixing conductanceenhancements. This latter quantity depends on the imaginary part of the transverse spin
susceptibility of the spin sink which is known to vary around critical temperatures. By
spotting the spin pumping peak we also determined the thickness dependence of the IrMn
critical temperature and deduced the characteristic length for the spin-spin interactions [5],which has been inaccessible to experiments. By highlighting the feasibility of detecting
magnetic phase transitions by spin pumping this work opens a new pathway for the deeper
investigation of non-trivial magnetic orders such as antiferromagnetism, with no net magnetic
moment and potentially large magneto-transport effects [6].
[1] L. Frangou, S. Oyarzun, S. Auffret, L. Vila, S. Gambarelli, and V. Baltz, “Enhanced spin pumping by
antiferromagnetic IrMn thin films around the magnetic phase transition,” arXiv:1509.03462 (2015).
[2] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, and B. I. Halperin, “Nonlocal magnetization dynamics inferromagnetic heterostructures,” Rev. Mod. Phys. 77, 1375 (2005).
[3] P. Merodio, A. Ghosh, C. Lemonias, E. Gautier, U. Ebels, M. Chshiev, H. Béa, V. Baltz, and W. E. Bailey,“Penetration depth and absorption mechanisms of spin currents in Ir20Mn80 and Fe50Mn50 polycrystalline
films by ferromagnetic resonance and spin pumping,” Appl. Phys. Lett. 104, 032406 (2014).
[4] Y. Ohnuma, H. Adachi, E. Saitoh, and S. Maekawa, “Enhanced dc spin pumping into a fluctuating
ferromagnet near TC,” Phys. Rev. B 89, 174417 (2014).
[5] R. Zhang and R. F. Willis, “Thickness-dependent curie temperatures of ultrathin magnetic films: Effect of
the range of spin-spin interactions,” Phys. Rev. Lett. 86, 2665 (2001).
[6] J. Železný, H. Gao, K. Výborný, J. Zemen, J. Mašek, A. Manchon, J. Wunderlich, J. Sinova, and T.
Jungwirth, “Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets,” Phys. Rev.
Lett. 113, 157201 (2014).

Change of Critical Exponent Near Transition Temperature from Bulk
to Surface Behaviour in Thin-Film Antiferromagnetic Cr2O3
Muftah Al-Mahdawi1, Yohei Shiokawa1, Satya P. Pati1, Tomohiro Nozaki1, andMasashi Sahashi1
1Department of Electronic Engineering, Tohoku University, Sendai 980-8579,
Japan
Antiferromagnets (AFM) have zero magnetization. This means they are stable against appliedmagnetic field, which is advantageous for data retention, but problematic for reading and writing. One
way is to utilize the exchange coupling with a ferromagnetic layer as a readout, and control AFM domain
by another external stimulus, e.g. electric field. This succeeded in the typical antiferrmagnetic
magnetoelectric material chromia (Cr2O3) [1].

Chromia is an AFM with spins aligned
parallel to c-axis, with spins at the same cplane pointing along the same direction. It
was reported that Cr2O3 changes behaviour
from 3D bulk-like to 2D surface-like near
Neel temperature (TN) inferred frommeasurements on exchange-bias of a Co
layer [2]. Such assertion is difficult only
from exchange-bias measurement. So we
measuredthemagnetoelectricsusceptibility (α) versus temperature near TN of a bulk Cr2O3 crystal and a 500-nm thinfilm single-layer sample (see figure). We extracted the criticality exponent (β) fromfitting to a power law (solid lines with fitting range indicated by arrows). For bulk
crystal, bulk behaviour was obtained. For a thin-film, β changes from a value (0.402)
close to bulk value at lower temperature, to a value closer to 2D (0.719) near TN. A
possible explanation is the distribution of TN in the film plane, that would give a similarchange of β when some domains become paramagnetic near the average TN. The same
effect can be argued against the observation made on Co/Cr2O3 exchange couplingsystem, with distribution in exchange interaction at the interface. We will present morediscussion and details on which is the origin. This work was partly funded by ImPACT
Program of Council for Science, Technology and Innovation (Cabinet Office, Japan
Government).
[1] Borisov et al., Phys. Rev. Lett. 94, 117203 (2005).
[2] Borisov and Kleemann, J. Appl. Phys. 110, 033917 (2011).

Current induced effects in structures with ultra-thin IrMn antiferromagnet
H. Reichlová,1, 2 D. Kriegner,2 V. Holý,2 K. Olejnı́k,1 V. Novák,1 M. Yamada,3K. Miura,3 S. Ogawa,3 H. Takahashi,3 T. Jungwirth,1, 4 and J. Wunderlich1, 51Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic
2

Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic
3

4

Hitachi Ltd., Central Research Laboratory, Kokubunju-shi, Tokyo, Japan

School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
5

Hitachi Cambridge Laboratory, Cambridge CB3 0HE, United Kingdom

Relativistic current induced torques and devices utilizing antiferromagnets have been independently considered as two promising new directions in spintronics research. Here we report electricalmeasurements of the torques in structures comprising a ∼ 1 nm thick layer of an antiferromagnet
IrMn. The reduced Néel temperature and the thickness comparable to the spin-diffusion length
allow us to investigate the role of the antiferromagnetic order in the ultra-thin IrMn films in theobserved torques. In a Ta/IrMn/CoFeB structure, IrMn in the high-temperature phase diminishes
the torque in the CoFeB ferromagnet. At low temperatures, the antidamping torque in CoFeB
flips sign as compared to the reference Ta/CoFeB structure (shown in Fig. 1 (a) and (b)), suggesting that IrMn in the antiferromagnetic phase governs the net torque acting on the ferromagnet.
At low temperatures, current induced torque signatures are observed also in a Ta/IrMn structure
comprising no ferromagnetic layer (shown in Fig. 1 (c)).

FIG. 1. (a) Current density j-dependence of the out-of-plane field HAD (black dots) in the reference
Ta/CoFeB sample. (b) Same as for the Ta/IrMn/CoFeB sample at 5 K (black dots) and 300 K (orange2ωdots). (c) Temperature-dependent difference in the Rxy
signal measured while cooling the sample in applied

in-plane and and out-of-plane magnetic fields of 2 T.

Thermally-Activated Phase Slips in Superfluid Spin Transport in
Magnetic Wires
Se Kwon Kim, So Takei, and Yaroslav Tserkovnyak
Department of Physics and Astronomy,
University of California, Los Angeles, California 90095, USA
We theoretically study thermally-activated phase slips in superfluid spin transport ineasy-plane magnetic wires within the stochastic Landau-Lifshitz-Gilbert
phenomenology, which runs parallel to the Langer-Ambegaokar-McCumber-Halperin
theory for thermal resistances in superconducting wires. To that end, we start byobtaining the exact solutions for free-energy minima and saddle points. We provide ananalytical expression for the phase-slip rate in the zero spin-current limit, which
involves detailed analysis of spin fluctuations at extrema of the free energy. An
experimental setup for a magnetoeletric circuit is proposed, in which thermal phase slips
can be inferred by measuring nonlocal magnetoresistance.
[1] S. K. Kim, S. Takei, and Y. Tserkovnyak, arXiv:1509.00904

Phenomenology of dynamics in noncollinear antiferromagnets IrMn3
Libor Šmejkal,(1,2) Olena V. Gomonay,(3,4) and Tomáš Jungwirth(1,5)
1Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, CZ-16253 Praha 6, Czech Republic
Department of Condensed Matter Physics, Charles University, Faculty of Mathematics and Physics, Ke Karlovu 5, CZ-12116
Prague 2, Czech Republic
3
Institute of Physics and Technology, National Technical University of Ukraine, 03056 Kyiv, Ukraine
4
Institut für Physik, Johannes Gutenberg Universität Mainz, D-55099 Mainz, Germany
5
School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom

2

The magnetic structure of the thin films of IrMn has been probed experimentally quite recently.1
These materials are particularly interesting due to the high Néel temperature (up to 1000 K), strong

Figure Error! No sequence specified. Three magnetic sublattices of IrMn3 in ground state lie
within the (111) plane.
exchange bias and pronounced spin-orbit coupling effects,2 therefore they are used for instance as apinning layers in spin valves. Recently the relativistic current induces torques have been measured
in the ultrathin layers of IrMn in the Ta/IrMn/CoFeB structure.3
The main part of the poster is focused on the phenomenology of noncollinear antiferromagnetic(AFM) order dynamics. We show that noncollinear AFM order (see Fig. 1) can be triggered via
antidamping like torque 𝑇𝑚×𝑚×𝑝,where 𝑚 is sublattice magnetization and 𝑝 is nonequilibrium spinpolarization. We proposed a mechanism of the ultrafast large angle reorientation between two
metastable states distinguishable by anisotropic magnetoresistance.4 It is theoretically demonstrated
that the dynamics might be restricted to the quazi-one-dimensional case. The estimation of thecritical current densities, magnetic anisotropy energy landscape and other material parameters
necessary for the succesful observation of the proposed effect are calculated from the fully
relativistic first principles.
Presented findings together with predictions of large galvanomagnetic effects4,5 makes noncollinear
AFM particularly appealing to experimental studies of current induced dynamics.
[1] A. Kohn, A. Kovacs, R. Fan, G. J. McIntyre, R. C. C. Ward, and J. P. Go. The antiferromagnetic structures of IrMn3
and their influence on exchange-bias. Scientic Reports, 3:2412, August 2013.
[2] L. Szunyogh, B. Lazarovits, L. Udvardi, J. Jackson, and U. Nowak. Giant magnetic anisotropy of the bulk
antiferromagnets IrMn and IrMn3 from first principles. Phys. Rev. B, 79:020403, Jan 2009.
[3] H. Reichlova, D. Kriegner, V. Holy, K. Olejník, V. Novak, M. Yamada, K. Miura, S. Ogawa, H. Takahashi, T.
Jungwirth, and J. Wunderlich. Current induced torques in structures with ultra-thin IrMn antiferromagnet. ArXiv eprints, March 2015.
[4] L. Šmejkal et al., unpublished.
[5] Hua Chen, Qian Niu, and H. MacDonald, A. Anomalous Hall effect arisising from noncollinear
antiferromagnetism. Phys. Rev. Lett., 112:017205, Jan 2014.

Electrical manipulation of a ferromagnet by an antiferromagnet
V. Tshitoyan1, C. Ciccarelli1, A. P. Mihai2,*, M. Ali2, A. C. Irvine1, T. A. Moore2, T. Jungwirth3,4, A. J. Ferguson1
1

Microelectronics Group, Cavendish Laboratory, University of Cambridge, CB3 0HE, UK
School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
3
Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6, Czech Republic
4
School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
2

Abstract
Several recent studies of antiferromagnetic (AFM) spintronics have focused on transmission and detection of
spin-currents in AFMs. Efficient spin transmission through antiferromagnets was inferred from experiments inferromagnet/antiferromagnet/normal metal (FM/AFM/NM) structures [1-3]. Measurements in FM/AFM bilayers
have demonstrated that a metallic AFM can also act as an efficient ISHE detector of the spin-current injectedfrom the FM, with comparable spin-Hall angles to heavy NMs [4,5]. Here we demonstrate that an antiferromagnet
can be employed for a highly efficient electrical manipulation of a ferromagnet [6]. We use an all-electricalexcitation and detection technique of ferromagnetic resonance in a NiFe/IrMn bilayer. At room temperature, we
observe antidamping-like spin torque acting on the NiFe ferromagnet, generated by the in-plane current driven
through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hallangle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the
NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the antiferromagnetic order in IrMn
governs the observed phenomenon.

References:[1] Wang, H., Du, C., Hammel, P. C. & Yang, F. Antiferromagnonic Spin Transport from Y3Fe5O12 into NiO.
Physical Review Letters 113, 097202 (2014).
[2] Hahn, C. et al. Conduction of spin currents through insulating antiferromagnetic oxides. EPL (Europhysics
Letters) 108, 57005 (2014).
[3] Moriyama, T. et al. Spin-transfer-torque through antiferromagnetic IrMn. arXiv:1411.4100[4] Mendes, J. B. S. et al. Large inverse spin Hall effect in the antiferromagnetic metal Ir20Mn80. Physical Review
B 89, 140406 (2014).
[5] Zhang, W. et al. Spin Hall Effects in Metallic Antiferromagnets. Physical Review Letters 113,196602 (2014).
[6] Tshitoyan, V. et al. Electrical Manipulation of a ferromagnet by an antiferromagnet. arXiv:1502.04570*Currently at London Centre for Nanotechnology, Department of Materials, Imperial College
London, SW7 2BP, UK

Effect of field-like spin orbit torque on spin sublattices of ultra-thinpolycrystalline FeMn films
Yumeng Yang1,2, Yanjun Xu1, Xiaoshan Zhang1, Ying Wang1, Shufeng Zhang3,
Run-Wei Li4, Meysam Sharifzadeh Mirshekarloo2, Kui Yao2, and Yihong Wu1
1

Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive
3, Singapore 117583, Singapore
2
Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research),
3 Research Link, Singapore 117602, Singapore
3
Department of Physics, University of Arizona, Tucson, Arizona 85721, USA
4
Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Materials Technology andEngineering, Chinese Academy of Sciences, Ningbo 315201, People's Republic of China

Spin orbit torque (SOT) in ferromagnet (FM)/heavy metal (HM) bilayers has been reported to bea promising alternative to spin transfer torque for switching magnetization directly by an inplane current. A natural question to ask is whether similar SOT effect can affect the spin
sublattices or magnetic order of antiferromagnet (AFM). To this end, we have fabricated a seriesof Pt/FeMn bilayers with different thicknesses and investigated how the spin sublattices of FeMn
can be altered by a current using the planar Hall effect (PHE). A large SOT effective field of
2.05×10-5 - 2.44×10-5 Oe/(A/cm2) is obtained for FeMn in the thickness range of 2 nm - 5 nm.
The experimental observations can be reasonably accounted for by using a macrospin model
under the assumption that the FeMn layer is composed of two spin sublattices with unequalmagnetization. The uncompensated net magnetization, originating from both the thin FeMn layer
and proximity induced moment in Pt, is much smaller than the magnetization of a typical FM;
this leads to a much larger SOT effective field in FeMn. The uncompensated spins provide aconvenient mechanism to probe the SOT effect in AFM using PHE. To further confirm theinteraction of spin current with FeMn, we fabricated Pt/FeMn/NiFe trilayers and investigate how
far the spin current generated in Pt can travel across the FeMn layer. It was found that the spincurrent can only travel through the FeMn layer with a thickness smaller than 4 nm. By
quantifying the field-like effective field induced in NiFe in the trilayers, a spin diffusion lengthof 2 nm is obtained for FeMn. This value is in good agreement with those reported in literature
obtained by other techniques. Although it remains a challenge to achieve a well-defined AFM
order for ultrathin FeMn films, our results do demonstrate that SOT can potentially be a usefultechnique for manipulating the spin states of AFM.

Antiferromagnetism: creative applications for the invisible magnets
X. Marti1
1

Institute of Physics ASCR, v.v.i., Prague 6 162 53, Czech Republic

In 1970, at the time when compact cassettes made it to the market after a century of experimenting
with ferromagnetic storage, the Nobel Prize was awarded for the “fundamental work and discoveries
concerning antiferromagnetism”. Louis Neel pointed out in his Nobel lecture that while abundant andinteresting from a theoretical viewpoint, antiferromagnets did not seem to have any applications.
Indeed, the alternating directions of magnetic moments on individual atoms and the resulting zero net
magnetization make antiferromagnets hard to control by tools common in ferromagnets. While
preoccupied with the inherent difficulties to read and write magnetic information in antiferromagnets,
scientists and engineers have largely overlooked the positive sides of antiferromagnets as being
magnetically invisible [1] and uniquely robust against magnetic perturbations [2, 3]. In this talk, we will
review recent developments in the emerging field of antiferromagnetic spintronics [4], retracing thefootsteps of the ferromagnetic based technologies. We will examine the path starting from seminal
basic science down to a survey of the potential markets for the coming up invisible magnetism.
[1] https://www.youtube.com/watch?v=X1Ft_OnRaq4[2] https://www.youtube.com/watch?v=HWZLJ02sb0U[3] Room-temperature antiferromagnetic memory resistor. X. Marti et al., Nature Materials 13, 367–374(2014)[4] Prospect for Antiferromagnetic Spintronics. X. Marti et al., IEEE Transactions on Magnetics 51(4),2900104 (2015)