bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic states of magnetite from photoemission spectroscopy ARUPS
Authors: Zalecki R. , Kołodziejczyk A. , Kozłowski A. , Korecki J. , Spiridis N. , Kąkol Z.
Published: January 2006

The valence band photoemission spectra of epitaxially grown film and bulk single crystal of magnetite were measured by the angle‐resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K and 120 K. Four main features of the electron photoemission were observed at about –1.0 eV, –3.5 eV, –5.0 eV and –6.5 eV below the chemical potential; they are rather strongly dependant on structure and preparation of surface. The three higher‐energy features showed significant energy dispersion. The ARUPS spectra were compared to the accessible band structure calculations. Special attention was paid to the leading edge of the emission at –1.0 eV of the low‐temperature spectrum where an insulating gap should be observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New orthorhombic multiferroics R1–xYx MnO3 (R = Eu, Gd)
Authors: Ivanov V. Yu. , Mukhin A. A. , Travkin V. D. , Prokhorov A. S. , Popov Yu. F. , Kadomtseva A. M. , Vorob'ev G. P. , Kamilov K. I. , Balbashov A. M.
Published: January 2006

A tendency to form multiferroic states with a spatially modulated antiferromagnetic structure and electric polarization in pure orthorhombic manganites RMnO3 upon decreasing of the rare‐earth ionic radii has been realized in single crystals of substituted compounds Eu1–x Yx MnO3 (0.2 ≤ x ≤ 0.5) and Gd1–y Yy MnO3 (0 ≤ y ≤ 0.2). While the parent pure and slightly substituted (x ≤ 0.1) compounds exhibited a spontaneous transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA < T N = 45–50 K, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock < T N for x ≥ 0.3 and y ≥ 0.05 accompanied by dielectric anomalies. Various phase transitions were observed in magnetic fields up to 250 kOe along the a ‐, b ‐, c ‐axes by magnetization, magnetostriction and electric polarization measurements. The latter indicate the existence of a spontaneous electric polarization below T lock. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymmetric magnetization reversal in exchange‐biased Co/Pt multilayers
Authors: van Dijken Sebastiaan , Czapkiewicz M. , Zoladz M. , Stobiecki T.
Published: January 2006

A detailed study of the magnetization reversal process in [20 Å Pt/t Å Co]3/100 Å IrMn/20 Å Pt multilayers with 4 Å ≤ t ≤ 9 Å is presented. The hysteresis of as‐deposited films with t ≥ 5 Å is found to be asymmetric. This asymmetry is explained by a lateral variation in the perpendicular exchange bias direction due to the growth of IrMn onto multi‐domain Co/Pt multilayers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Double exchange model in cubic vanadates
Authors: Wohlfeld Krzysztof , Oleś Andrzej M.
Published: January 2006

We investigate the role of the double exchange mechanism for stability of the metallic C‐type antiferromagnetic (C‐AF) phase, which was observed experimentally in hole doped La1–x Srx VO3. The double exchange model treats localized electrons in xy orbitals as classical S = 1/2 spins, which interact by Hund's exchange J H with yz /zx electrons in partly filled t 2g orbitals. Including strong on‐site Coulomb repulsion U between t 2g electrons, and using slave boson method we demonstrate that C ‐AF and metallic phase can be stabilized due to the specific features of the hopping in degenerate and partly filled t 2g orbitals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The properties of the CDW phase in the weak coupling anharmonic Holstein–Hubbard model
Authors: Grzybowski P.
Published: January 2006

The anharmonic Holstein–Hubbard Hamiltonian in the case of weak effective electron–electron attraction is studied. To deal with anharmonicity of phonons, variational canonical transformations are used to derive an effective electron Hamiltonian. The properties of the charge density wave (CDW) phase, for half‐filling, are analyzed using this effective Hamiltonian. In particular, the critical temperatures, gap function, order parameter and gap ratio are calculated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Properties of the extended Hubbard model with transverse (XY‐type) spin‐exchange interaction
Authors: Czart W. R. , Robaszkiewicz S.
Published: January 2006

The properties of the extended Hubbard model with transverse (XY‐type) spin‐exchange intersite interaction (J ⊥) are studied. The cases of ferromagnetic and antiferromagnetic XY exchange are considered. The analysis of the model is performed for d ‐dimensional hypercubic lattices 2 ≤ d ≤ ∞, by means of the (broken symmetry) Hartree–Fock approximation supplemented, for d = ∞, by the slave‐boson mean‐field method. The effects of phase fluctuations on T c of XY phases for d = 2 lattices are estimated within the Kosterlitz–Thouless scenario. Qualitative differences between the properties of the ferromagnetic and antiferromagnetic XY phases are pointed out. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Giant magnetoresistance effect in quantum nano‐scale wires
Authors: Chudzinski P. , Krompiewski S.
Published: January 2006

We study transport properties of nano‐scale wires connected to ferromagnetic semi‐infinite electrodes in the ballistic regime. Systems with different geometries are considered. Our method is based on recursive Green's function technique. We fully deal with atomistic structure of the whole system, treating both the nano‐wire and the electrodes on equal footing. The results include the transmission, with parallel and antiparallel magnetization in the electrodes, and giant magnetoresistance (GMR) vs. energy. The influence of the magnetic polarization, coupling between the nano‐wire and the electrodes as well as the geometry of the device on transport properties are discussed. We emphasize the shape dependent effects and take into account also imperfect structures with some atoms removed from the central region. In addition to evolution from conductance quantization to resonant tunneling regime (upon changing the hopping parameter), it has been found that with increasing polarization other features appear due to decreasing overlap between surface density of states of propagating modes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetization studies of HoCo0.51Mn0.49O3 single crystals
Authors: Aleshkevych P. , Baran M. , Barilo S. N. , Gatalskaya V. I. , Shiryaev S. V. , Szymczak R. , Szymczak H.
Published: January 2006

The low‐temperature magnetic properties of the orthorhombic HoMn0.49Co0.51O3 single crystals grown by the electrodeposition method have been investigated. From an analysis of magnetization results two types of phase transitions were found. The first‐order transition is connected with ferromagnetic ordering (the Curie temperature T C = 83 K). The second‐order transition accompanied by spontaneous spin reorientation was found within the 20–30 K range of temperature. The spin reorientation was explained in the framework of the phenomenological molecular field model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The origin of low‐dimensional magnetism in Cu(en )2Pt(CN)4
Authors: Tibenská K. , Orendáčová A. , Čižmár E. , Park J.‐H. , Lančarič Š. , Orendáč M. , Anders A. G. , Vavra M. , Potočňák I. , Feher A. , Meisel M. W.
Published: January 2006

Magneto‐structural correlations in Cu(en )2Pt(CN)4 (en = C2H8N2) have been investigated by experimental studies of the magnetic properties and hydrogen bond geometry. The analysis of electron paramagnetic resonance spectra confirmed the d z2 electronic ground state of Cu(II) ion expected from room temperature X‐ray measurements. Magnetization and susceptibility data indicate the presence of weak exchange coupling J /k B = –0.4 K. Consequently, a spin diffusive regime in the spin relaxation can be expected at 4 K, and the angular dependence of the linewidth can be qualitatively explained by considering two‐dimensional magnetic behaviour. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase diagram of hard‐core bosons with both diagonal and Mattis‐type off‐diagonal disorder
Authors: Grzybowski P. , Chhajlany R. W.
Published: January 2006

We reanalyze the phase diagram of a hard‐core boson system with diagonal and Mattis‐type off‐diagonal disorder in a general setting. We report differences with respect to previously presented results. In an extended model, we have found an additional continuous transition not present in the previously studied case. We also comment on the influence of the interplay between the diagonal and off‐diagonal disorder on the existence of the localization transition. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the BCS‐to‐Bose crossover in 2D anisotropic superconductors
Authors: Tobijaszewska B. , Micnas R.
Published: January 2006

We analyze the competing pairings and crossover from BCS to local pair (LP) superconductivity for the d‐wave pairing symmetry in the ground state. The phase diagrams for the extended Hubbard model with intersite electron pairing and hard‐core repulsion (U = ∞) are obtained for the 2D square lattice. The influence of the nnn hopping (t 2) on the crossover is discussed. For appropriate values of the parameters (nnn repulsion) and |t 2/t | < 0.5 the crossover is simultaneous with the vanishing of nodal points in the quasiparticle energy. The vanishing of nodal points is clearly reflected in the evolution of the presented superconducting characteristics. Results for d pairing are compared with those for the crossover in the s*‐wave channel and the role of chiral px + i py states is also discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monte‐Carlo simulation of solid state and melting of 2D confined magnetic particles under perpendicular field
Authors: Levy Jean‐Claude S. , Ghazali Abdelwahab
Published: January 2006

Numerous systems correspond to confined magnetic particles interacting through dipolar interactions: magnetic particles, flux lines in superconductors, charged colloids. From careful extended Monte‐Carlo simulations the ground state is obtained and shown to be derived from a triangular lattice with a few layers stuck to the confinement boundary. The most common solid state obtained by relaxation from a random configuration is found to be an excited state composed of many triangular crystallites separated by lines of alternate topological defects with five and seven nearest neighbours. The melting of these two solid phases gives a common liquid phase. But the melting of the ground state is a sharp first order transition while the melting of the excited state is a continuous vitreous transition which starts at low temperature with the motion of topological defects on their defect lines, while the rest of the sample remains solid, as a two component medium. The elastic properties of these solid states under shear are also considered. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current‐induced spin dynamics in spin‐valve structures
Authors: Gmitra M. , Horváth D. , Wawrzyniak M. , Barnaś J.
Published: January 2006

The Landau–Lifshitz–Gilbert equation for the magnetization dynamics, extended by including the torque due to spin‐transfer from conduction electrons, is used to study current‐induced magnetic switching and stationary precessional modes. The spin torque is described in terms of a macroscopic model based on the classical spin diffusion equations and relevant boundary conditions. The approach allows to investigate current‐driven switching, in particular the switching time and the frequency of the associated magnetoresistance signal in the precessional regime. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of hydrogen bonds on magnetic properties of Cu(dmen )2M(CN)4 (M = Ni, Pt) S = 1/2 low‐dimensional Heisenberg antiferromagnets
Authors: Čižmár E. , Orendáčová A. , Orendáč M. , Kuchár J. , Vavra M. , Potočňák I. , Černák J. , Casini E. , Feher A.
Published: January 2006

The magneto‐structural correlations in materials Cu(dmen )2M(CN)4, where M = Ni or Pt, and dmen is N,N‐dimethylethylenediamine, have been investigated. Specific heat, susceptibility, magnetization and ESR studies of both materials suggest the presence of a weak antiferromagnetic (AFM) exchange interaction. Observed l ‐like anomaly at T max = 0.2 K in the temperature dependence of the specific heat of studied materials might be attributed to the formation of long‐range order due to the presence of exchange coupling between the planes. The entropy removed above the transition temperature represents 50% of the total magnetic entropy suggesting low‐dimensional character of the system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal stability of amorphous structure and magnetic properties Fe80–xCoxP14B6 (x = 20–40) ribbons
Authors: Kostyrya S. A. , Idzikowski B. , Tkatch V. I. , Popov V. V. , Rassolov S. G.
Published: January 2006

Amorphous structure and its thermal stability as well as magnetic properties of Fe80–x Cox P14B6 (20 ≤ x ≤ 40) glasses have been studied by X‐ray diffraction, non‐isothermal differential scanning calorimetry (DSC) and thermomagnetic (TMG) measurements. The Curie temperature increases with Co content, while the glass transition and crystallization onset temperatures decrease. As a result, for alloys x = 30, 32 and 35 at%, the transition into paramagnetic state take place close to glass transition temperature. However, for x = 40 at% the TMG curve, in the vicinity of magnetic transition temperature, is overlapped by ferromagnetic crystallization products. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural, magnetic and hyperfine parameters of B2‐type FeAl compounds doped with transition metal additions
Authors: Michalecki T. , Deniszczyk J. , Frackowiak J. E.
Published: January 2006

The structural, electronic and magnetic properties of the transition metal (TM = Ti, V, Cr, Mn, Co, Ni, Cu, Zn) alloying additions in FeAl compound with B2 structure have been investigated with tight‐binding linear muffin‐tin orbital (TB‐LMTO) method. The site preference of the TM additions was investigated for (Fe0.44TM0.06)Al0.50 and Fe0.50(Al0.44 TM0.06) compositions. Both magnetically ordered and non magnetic solutions were analysed. The analysis has shown that the elements (Ti, V, Cr, Mn) slightly more prefer the Al sublattice, whereas the (Co, Ni, Cu, Zn) atoms have a distinct preference for the Fe sublattice. The local magnetic moment of the additions located at the Al sites shows an antiferromagnetic alignment with respect to the bulk magnetization. The dependence of the isomer shift and hyperfine magnetic field for 57Fe nucleus on the TM valence is analysed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of substituted SrRuO3
Authors: Dabrowski B. , Kolesnik S. , Chmaissem O. , Maxwell T. , Mais J. , Jorgensen J. D.
Published: January 2006

We have investigated structural and magnetic properties of the SrRu1–v O3 and SrRu1–x Crx O3 perovskites with uniquely suppressed and increased ferromagnetic transition temperatures, respectively. Polycrystalline samples synthesized in 600 atm. O2 at 1100 °C and in air at 1340 °C reach the v and Cr solubility limits at v ∼ 0.10 and x = 0.15, respectively. The ordered moment is dramatically suppressed by the creation of Ru vacancies. The linear decrease of the lattice parameters and bond lengths, and an increase of the bond angles with increasing x are due to substitution of the smaller Cr4+/3+ ion for Ru4+/5+. Similar decreases of the molar susceptibility, χ m, in the paramagnetic region above T C and the high‐field magnetization at 5 K with x also indicate the presence of the Cr4+/3+ and Ru4+/5+ ions. These results confirm that the Ru4+/5+(d4/3)–O2––Cr4+/3+(d2/3) minority band double‐exchange interaction that involves the Cr3+ and Cr4+ in the magnetic ordering is responsible for the enhanced ordering temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of almost localized fermions revisited: spin dependent masses and quantum critical behavior
Authors: Spałek Jozef
Published: January 2006

The magnetic properties of almost localized (heavy) quasiparticles have been a subject of renewed interest in recent years. This is caused by the discovery of spin dependent masses predicted by us some time ago, as well as quantum critical behavior at the metal–insulator boundary. We discuss those phenomena, as well as metamagnetic behavior. These phenomena are discussed by regarding Gutzwiller approach (in the slave‐boson version) as the mean‐field approach to the correlated electron systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of almost localized fermions revisited: spin dependent masses and quantum critical behavior
Authors: Spałek Jozef
Published: January 2006

The Editor's Choice [1] of this issue of physica status solidi (b) discusses spectacular phenomena in correlated electron systems viewed as quantum materials. The cover figure is a schematic representation of the transformation from the Kondo insulator (KI) state to the non‐Fermi liquid (NFL) state with short‐range antiferromagnetic correlations at the critical concentration, when the Kondo singlet state is destroyed. AFI denotes the antiferromagnetic insulating state.

The author Jozef Spałek heads the Condensed Matter Theory Division in the Institute of Physics of the Jagiellonian University Kraków. His scientific interests include the theory of Mott–Hubbard and heavy‐fermion systems, with a particular emphasis on quantum critical behavior close to the electron localization.

This issue contains presentations from The European Conference Physics of Magnetism (PM'05) held in Poznań, Poland, 24–27 June 2005. Further articles from PM'05 can be found in phys. stat. sol. (c) 3, No. 1 (2006).
Bond‐ordered, bond‐centered stripes in cuprates
Authors: Maciąg A. , Wróbel P. , Eder R.
Published: January 2006

Using a combination of the bond formalism and the string picture we analyze the stability of bond‐ordered, bond‐centered stripe system formed in the doped two dimensional (2D) antiferromagnet (AF). Our interest in such structures is motivated by results of recent neutron scattering experiments. We concentrate especially on a stripe, in which bond order takes the shape of a two‐layer brick wall, forming a domain wall (DW) between AF domains with the changing by π across each DW direction of the sublattice magnetization. By analyzing the energy of such a structure and comparing with energies of stripes with other patterns of the underlying magnetic background we draw the conclusion that at the doping level 1/8 the most stable is the system of DWs which takes the form of two‐leg ladders with bond‐ordered nearest parallel legs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐band ferromagnetic Kondo lattice model on a ladder with quantum S = 3/2 core spins
Authors: Neuber D. R. , Daghofer M. , Olés Andrzej M. , von der Linden Wolfgang
Published: January 2006

The interplay of spin and orbital correlations in doped manganites is investigated on a ladder described by the ferromagnetic (FM) Kondo model. Upon doping, the one‐band model exhibits phase separation into an antiferromagnetic (AF) background due to t 2g superexchange J ′ and either a hole‐rich FM phase or islandlike region of antiferromagnetically stacked polarons. In contrast, separated polarons are favored by the two‐band model at low doping. For suitable parameters, both the one‐orbital and two‐orbital model yield FM chains with AF coupling between them, reminiscent of the C ‐AF phase observed in manganites. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Intrinsic mechanism of anomalous Hall effect in a twodimensional magnetic system with impurities
Authors: Dugaev V. K. , Bruno P. , Taillefumier M. , Canals B. , Lacroix C.
Published: January 2006

We report some new results on the Anomalous Hall effect induced by the Berry phase in momentum space. Our main calculations are performed within the model of a two‐dimensional electron gas with the spin‐orbit interaction of Rashba type, taking into account the scattering from impurities. We demonstrate that such an “intrinsic” mechanism can really dominate but there is a competition between the geometric Berry‐phaseinduced term σ II xy in the Hall conductivity and the impurity‐induced term σ I xy , related to the contribution of the states in the vicinity of the Fermi surface. We also show that the contribution to the Hall conductivity from the electron states close to the Fermi surface has the intrinsic property as well, and it does not vanish in the clean limit. The main effect of the impurity‐related contribution is a possible change of sign of the off‐diagonal conductivity. The resulting magnitude and sign of the Hall conductivity strongly depend on the electron density in the system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Domain structure and magnetoresistance of NiFe/Au/Co/Au multilayers with perpendicular anisotropy
Authors: Urbaniak Maciej , Stobiecki Feliks , Engel Dieter , Szymański Bogdan , Ehresmann Arno , Kim JinBae
Published: January 2006

The magnetic properties of sputtered [Ni80Fe20(2 nm)/Au(t Au)/Co(t Co)/Au(t Au)]15 multilayers with t Au = 1.5‐3 nm and t Co =0.6‐1.5 nm were investigated with magnetic force microscope. The Ni80Fe20 layers possessed in‐plane magnetic anisotropy while the sandwiching of Co layers between Au layers ensured their perpendicular anisotropy through the influence of surface anisotropy. It led to the formation of a maze configuration of stripe domains. The stripe domains period λ strongly depends on t Co changing from 0.9 to 0.3 µm when t Co changes from 0.6 to 0.8 nm. Period λ increases with Au layers thickness, too. The values of stray fields originating from Co layers which act on Ni80Fe20 layers, in the range of 100 kA/m, estimated from magnetoresistive dependencies are in qualitative agreement with those evaluated from the model of infinitely long stripe domains with domain widths taken from MFM measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical transport in strained La0.7Ca0.3MnO3 films
Authors: Markovich V. , Vlakhov E. S. , Yuzhelevskii Y. , Blagoev L. B. , Nenkov K. A. , Gorodetsky G.
Published: January 2006

Magnetotransport properties of La0.7Ca0.3MnO3 thin films deposited on (100) LaAlO3 substrate were investigated. Fine balance between the charge ordered insulating phase and ferromagnetic metallic phase results in a number of glassy features such as: significant hysteresis, memory effects and long‐time resistivity relaxation at turning on and off of magnetic field. It was found that in the temperature range 10–220 K the resistance of thin film decreases significantly upon applying electric current and this effect cannot be explained by homogeneous Joule heating. The magnetotransport properties of the thin films are discussed in the frame of cross‐coupling of charge, spin and strain. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin wave parameter in the system of non‐equivalent exchange coupled layers
Authors: Urbaniak‐Kucharczyk A. , Castillo Alvarado F. L.
Published: January 2006

The system of two ferromagnetic layers characterized by different exchange parameters and indirectly coupled by nonmagnetic spacer has been considered in low temperature region. The spin wave parameter B describing the Bloch's T 3/2 law has been calculated as a function of thickness and exchange parameters of constituent layers employing the Green fuction method. It has been shown that anisotropy in the interface region influences the dependence of B on the inverse thickness of the system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transport and magnetic characterization of La0.885Sr0.115MnO3/YBa2Cu3O7 superlattices
Authors: Tsarou A. , Komissarov I. , Dluzewski P. , Paszkowicz W. , Minikayev R. , Sawicki M. , Dabrowski B. , Kimaball C. , Przyslupski P.
Published: January 2006

We report on depression of superconducting transition temperature of YBa2Cu3O7 (YBCO) layers, when their thickness is reduced in proximity to ferromagnetic insulating La0.885Sr0.115MnO3 (FI‐LSMO) layers in [FI‐LSMO*8 u.c./YBCO*n u.c.]16 superlattices, where n = 1, 2, 4 and 6 unit cells (u.c.). The thickness of manganite FI‐LSMO layers is kept at 8 unit cells. Signature of antiparallel alignment between FI‐LSMO layers across YBCO spacer layers was observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐polarized surface states in semiconductor superlattices
Authors: Kłos Jarosław
Published: January 2006

Electronic surface states in Al0.1Ga0.9As|GaAs superlattice are calculated for a system with a ZnMnSe barrier in a surface cell. In the absence of applied magnetic field the ZnMnSe barrier has the same height as the Al0.1Ga0.9As barriers in the bulk cells. When a magnetic field is applied perpendicularly to the superlattice layers, the surface cell magnetic barrier height is found to vary with spin orientation. Hence, each spin polarization involves different conditions of surface state existence. Our computations show a split of Shockley states into two levels (corresponding to different spin polarizations) and appearance of Tamm states (with specific spin polarization), induced by sufficiently strong magnetic fields. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current induced switching due to spin‐transfer in spin valves: macroscopic model
Authors: Gmitra M. , Barnaś J. , Fert A. , Weymann I. , Dugaev V. K.
Published: January 2006

We develop a macroscopic description of current‐induced torque due to spin transfer in layered systems consisting of ferromagnetic films separated by a nonmagnetic layer. The description is based on the classical spin diffusion equations for the distribution functions inside the films used in the theory of CPP‐GMR, and macroscopic boundary conditions for the longitudinal and transverse components of the spin current. Due to strong exchange field in ferromagnetic films, we assume that the perpendicular component of spin current is totally absorbed within the narrow interface region giving rise to the torque. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kondo effect in spin‐dependent transport through a quantum dot for a finite correlation parameter U
Authors: Wilczyński M. , Świrkowicz R. , Barnaś J.
Published: January 2006

The Kondo effect in a system consisting of a QD coupled to non‐magnetic or ferromagnetic electrodes is studied theoretically in the framework of the non‐equilibrium Green function formalism. Variation of the Kondo anomaly in differential conductance with the correlation parameter U is analyzed in detail. Splitting of the Kondo peak in an external magnetic field and/or due to an effective exchange field created by ferromagnetic electrodes is also discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐polarized resonant tunneling through two coupled quantum dots
Authors: Trocha P. , Barnaś J.
Published: January 2006

Resonant electronic transport through two coupled non‐interacting single‐level quantum dots attached to ferromagnetic leads with collinear magnetizations is analyzed theoretically. Coupling of the dots to external leads as well as the inter‐dot coupling are assumed to be spin dependent. Basic transport characteristics, including current‐voltage curves, linear and nonlinear conductance, and tunnel magnetoresistance associated with magnetization rotation are calculated using the Green function technique. The relevant Green functions have been calculated by the equation of motion method. Variation of the transport characteristics with such system parameters like energy level position, spin polarization of the leads, and coupling between the dots has been calculated numerically. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic anisotropy and resonance linewidth of Fe3Si/GaAs(001)
Authors: Lenz K. , Kosubek E. , Baberschke K. , Herfort J. , Schönherr H.‐P. , Ploog K. H.
Published: January 2006

The magnetic anisotropy energy and the resonance linewidth of epitaxial Fe3Si grown on GaAs(001) is studied by ferromagnetic resonance (FMR) technique. For a nearly stoichiometric sample (25.5% Si‐content) a clear fourfold anisotropy is observed which is modulated by a small contribution of an uniaxial in‐plane anisotropy. This uniaxial component is found to increase with the Fe concentration in the intermetallic compound. The samples show an exceptional narrow resonance linewidth of only 17 Oe at 9 GHz excitation frequency confirming the very high structural quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic studies of Fe(III)–crosslinked chitosan
Authors: Nedelko N. , Ślawska‐Waniewska A. , Kaźmierczak J. , Rodrigues C. A. , Bordini C.
Published: January 2006

The low‐temperature dc and ac magnetic measurements of Fe(III)–crosslinked chitosan complexes are reported. The results obtained indicate a complex magnetic structure in which strong antiferromagnetic interactions coexist with weak ferromagnetism. Fe‐chitosan exhibits features of a glassy state as well as canted antiferromagnetism and its low temperature collective magnetic behaviour can result from the coexistence of these two types of ordering. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hyperfine interactions, magnetic, transport and structural properties of La0.67Ca0.33Mn0.9457Fe0.06O3
Authors: Przewoźnik J. , Żukrowski J. , Chmist J. , Tarnawski Z. , Kołodziejczyk A. , Krop K. , Kellner K. , Gritzner G.
Published: January 2006

The La0.67Ca0.33Mn0.9457Fe0.06O3compound was studied using powder X‐ray diffraction, VSM magnetometry, four‐probe resistance measurements and57Fe Mössbauer spectroscopy. The Mössbauer measurements were performed between 15 K and 850 K and showed good agreement between Curie temperature determined from temperature dependences of the hyperfine field (141 K) and DC magnetization (142 K). They show the inhomogeneous character of the magnetic transition and the coexistence of ferromagnetic and paramagnetic phases in the temperature range 110 K ≤T< 141 K. Our results confirmed that substitution of Fe3+for Mn3+strongly affects the magnetic and transport properties of the parent compound. It causes a difference between Curie temperature and the metal‐insulator transition temperature of about 80 K and a strong reduction of their values. X‐ray diffraction measurements were performed between 4 and 500 K and showed complete suppression of the thermal expansion anomaly at Curie temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic excitations in FCC Mn (37%Fe, 3%Cu) alloy
Authors: Mikke Kazimierz , Jankowska‐Kisielińska Joanna , Hennion Bernard
Published: January 2006

Within the program of our systematic studies of magnetic excitations of manganese alloys the inelastic neutron scattering in FCC Mn(37%Fe,3%Cu) was measured for the temperature range 1.7–600 K. This alloy has the FCC crystal structure both in paramagnetic and AF phase and its composition is close to the range where the enhanced itinerant behaviour was predicted by the theory. The measured spin‐wave velocity and the energy gap in the spin wave spectrum were reported earlier to reach the maximum values in this composition range. Our data did not confirm these earlier results. The expected anisotropy of the inelastic neutron scattering was not found neither in the antiferromagnetic phase nor in the paramagnetic one. The q‐dependence of the spin‐wave damping is quadratic rather than linear and the spin‐wave damping increase with temperature, as usually predicted for damping due to magnon scattering on magnons and on other excitations. This result is in contrast with the data for the FCT Mn(10%Fe,3%Cu) where the q‐dependence of the spin‐wave damping is linear and the damping parameter was found to be temperature independent excepting the region close to TN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic structure of RCoxGe2 (R=Ce, Pr, Gd) compounds
Authors: Penc B. , Szytuła A. , Wawrzyńska E. , Winiarski A.
Published: January 2006

The electronic structure of the RCoxGe2 (R=Ce, Pr, Gd) compounds with the orthorhombic crystal structure of CeNiSi2‐type was studied by X‐ray photoemission spectroscopy. The valence bands of CeCo0.86Ge2 and PrCo0.85Ge2 compounds have the similar character. Near the Fermi level the broad peak corresponding to the Co 3d and R 4f and 5d6s states is observed. In the case of GdCo0.64Ge2, the strong intensity peak at 8.7 eV corresponding to Gd 4f states is observed. The analysis of the XPS spectra of Ce and Pr 3d5/2 and 3d3/2 in the Gunnarson‐Schönhammer model give the information on the hybridization of the f orbital with the conduction band. The hybridization energy equal 93 eV for R=Ce and 143 eV for R=Pr, respectively indicate stability of the shell in these compounds. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase diagrams and multicritical points in the ternary mixed‐spin alloy with a single‐ion anisotropy
Authors: Dely J. , Bobák A.
Published: January 2006

The phase diagram of the ABpC 1–p ternary alloy consisting of different Ising spins SA = 3/2, SB = 2, and SC = 5/2 in the presence of a single‐ion anisotropy is investigated by the use of a mean‐field theory. At finite temperature by changing values of the parameters of the model different types of phase diagrams are obtained, including critical end points and isolated critical points. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The DC and AC insulating properties of magnetic fluids based on transformer oil
Authors: Tomčo L. , Marton K. , Herchl F. , Kopčanský P. , Potočová I. , Koneracká M. , Timko M.
Published: January 2006

The AC‐dielectric breakdown was investigated in magnetic fluids based on transformer oil TECHNOL US 4000 for two orientations of external magnetic field (B ‖ E and B ⊥ E) and in B = 0. The found results were compared with those obtained formerly for the DC‐dielectric breakdown. The observations of the time development of the AC‐dielectric breakdown showed the presence of partial discharges long before the complete breakdown occurrence, while for DC‐dielectric breakdown a complete breakdown of the gap next to the onset of a measurable ionization was characteristic. The comparison of the AC‐dielectric breakdown strengths of pure transformer oil and transformer‐oil‐based magnetic fluid showed better dielectric properties of magnetic fluid in external magnetic field and comparable, but not worse, in B = 0. Regarding to the better heat transfer, provided by magnetic fluids, they could be used in power transformers as insulating fluids. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized theoretical approach to quasi‐one‐dimensional molecular magnets
Authors: Pełka R. , Bałanda M. , Przychodzén P. , Tomala K. , Sieklucka B. , Wasiutyński T.
Published: January 2006

Two quasi‐one‐dimensional compounds [LnIII(terpy)(DMF)4][WV(CN)8] · 6H2O, where Ln stands for Gd or Sm, were synthesized and the measurements of their magnetic features were carried out. Magnetization was measured at 2K in the field range 0–5 T. To extract physical information from the experimental data a generalization of the theoretical approach given by Verdaguer et al. (Phys. Rev. B 29 , 5144 (1984)) [1] is put forward. That theoretical model is found to fit the data well. It allows for the determination not only of the coupling constant but also of the zero‐field splitting parameter. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New spin configurations in nano‐sized magnets near reorientation phase transition
Authors: Kisielewski M. , Maziewski A. , Zablotskii V.
Published: January 2006

We review the evolution of magnetization distributions in samples with low magnetic perpendicular‐anisotropy described by the quality factor Q (the relation between anisotropy and demagnetization energies). Infinite ultrathin films, nanowires and disks are studied using real magnetic parameters determined for ultrathin cobalt. By micromagnetic simulations we demonstrate novel types of magnetization distributions. Reconstructions of magnetization distributions at the spin reorientation transition (RPT) from the perpendicular to in‐plane state are discussed. We show that the sample edge significantly affects the magnetization distribution performance and shifts the RPT to lower Q (higher nanostructure thickness) and/or to higher amplitude of in‐plane applied magnetic fields in comparison to those in laterally infinite films. A unified thermodynamic treatment is presented for reorientation transitions in nanowires. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of Ni‐Mn‐Ga Heusler alloy films
Authors: Dubowik J. , Gościańska I. , Kudryavtsev Y. V. , Lee Y. P. , Sovák P. , Konĉ M.
Published: January 2006

The films with composition Nix Mny Gaz (x = 50 ± 5, y = 25 ± 5, z = 25 ± 5) were deposited by flash‐evaporation or sputtering on mica and glass substrates and annealed in a high vacuum at 673–973 K. X‐ray diffraction at room temperature reveals the presence of B2 (or L21) type of structure depending on annealing conditions. Magnetic properties were studied by ferromagnetic resonance at temperatures from 78 K to 400 K and compared with electric resistivity data. It is shown that the magnetic properties of the films critically depend on their structural ordering and microstructure. The films annealed at T < 800 K reveal a complex magnetic behavior due to their specific microstructure while those annealed at T > 800 K show magnetic properties comparable with those of bulk Ni‐Mn‐Ga alloys. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ground‐state properties of the three‐dimensional Falicov‐Kimball model
Authors: Farkašovský Pavol , Čenčariková Hana , Tomašovičová Natália
Published: January 2006

The ground‐state properties of the three‐dimensional spinless Falicov‐Kimball model are studied by a wellcontrolled numerical method. The results obtained are used to categorize the ground‐state configurations according to common features for weak, intermediate and strong interactions. It is shown that only a few configuration types form the basic structure of the phase diagram. In particular, the largest regions of stability correspond to phase segregated configurations, striped configurations and configurations in which electrons are distributed in diagonal planes with incomplete chessboard structure. Near half‐filling, mixtures of two phases with complete and incomplete chessboard structure are determined. In addition, the picture of metal‐insulator transitions is presented. The relevance of these results for a description of real material is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Critical sound propagation in MnF2
Authors: Pawlak A.
Published: January 2006

We analyse the critical sound attenuation in the antiferromagnet MnF2 above its Neel temperature. A general formula for the acoustic self‐energy, derived in the model in which a sound mode is coupled to both the order‐parameter fluctuations as well as to the energy mode, is applied to interpret the experimental data in MnF2. It has been shown that a very interesting competition between three asymptotic singularities is responsible for the complex behaviour of the sound attenuation coefficient in the high‐temperature phase. The relative strength of these terms depends also on the ultrasonic frequency. For high frequency sound propagation also a background attenuation starts playing an important role. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effective sound attenuation exponents in magnets
Authors: Pawlak A. , Fechner B.
Published: January 2006

We try to explain how some magnets belonging to the Heisenberg universality class can be characterised by positive sound attenuation exponents near the critical point. In magnets being also insulators the sound attenuation exponent should be equal to 2α where α is the usual specific‐heat exponent. This exponent is however negative in the Heisenberg universality class. In this paper we interpret the positive attenuation exponents measured in isotropic magnets such as RbMnF3, Y3Fe5O12 and Gd3Fe5O12 in terms of the effective critical exponents. The high value of the sound attenuation exponent in anisotropic FeF2 can also be interpreted in this way. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetization dynamics of perpendicular exchange‐biased (Pt/Co)‐Pt‐IrMn multilayers studied by MOKE microscopy and magnetometry
Authors: Czapkiewicz M. , van Dijken S. , Stobiecki T. , Rak R. , Zoladz M. , Mietniowski P.
Published: January 2006

In this paper the dynamics of the magnetization reversal process in perpendicularly biased [20 Å Pt/5 Å Co]3/t Å Pt/100 Å IrMn/20 Å Pt multilayers with different Pt insertion layer thickness (0 Å ≤ t ≤ 12 Å) is studied. The insertion of 1 Å thick Pt enhances the exchange bias field (Hex ) and for t > 3 Å Hex decreases exponentially with increasing Pt layer thickness. We show by magnetization relaxation measurements and direct observation of magnetic domains that magnetization reversal takes place by the nucleation of isolated cylindrical domains with a different nucleation site density in the forward and backward branches of the hysteresis loop. All the results were quantitatively analyzed using the Fatuzzo model for the dynamics of domain reversal processes. The activation energies for magnetization reversal by domain nucleation and domain propagation were determined. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The influence of roughness on some magnetic properties of layered structures of Fe, Co separated Cu or Au
Authors: Staniucha I. , Urbaniak‐Kucharczyk A.
Published: January 2006

The system of two magnetic (M) layers divided by nonmagnetic (N) spacer is considered. Roughness in interface region is introduced employing model proposed by Bruno and Chappert. Presence of roughness leads to modification of interface exchange parameter and interface anisotropy in comparison to samples with ideal interface. The magnetisation distribution and Curie temperature has been calculated using Green function formalism for systems consisting of Fe or Co standing for M and Cu or Au standing for N, respectively. Parameters corresponding to GaAs have been taken into account to characterize the substrate. The results obtained show decreasing of Curie temperature and shift of magnetisation curve with increasing of roughness parameter. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An extended Boltzmann formalism for transport description in thin Fe–Cr–Fe trilayers
Authors: Warda K. , Wojtczak L. , Baldomir D. , Pereiro M. , Arias J.
Published: January 2006

We present the calculations of Giant Magnetoresistance (GMR) for thin trilayers of the type nFe/3Cr/nFe where 1 ≤ n ≤ 8 for the slab geometry. All parameters used for the calculations in Boltzmann approach like the potentials, relaxation times, effective masses and the Fermi energy are determined for the different spin polarisations from electronic structure of trilayer on the base of ab initio method. The value of the parameter P corresponds to the specularity factor in Fuchs–Sondheimer theory. It is responsible for scattering electron from the metallic surface determined in analytical way. The results show a strong dependence of GMR on the ferromagnetic layer thickness as well as on the concentration of scattering centers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diode effect in transport through a quantum dot coupled to non‐collinearly polarized ferromagnetic leads
Authors: Rudziński W. , Świrkowicz R. , Wilczyński M. , Barnaś J.
Published: January 2006

Electron tunneling through a spin‐split discrete level of an interacting quantum dot coupled to two ferromagnetic electrodes with non‐collinear magnetizations is investigated theoretically by means of the nonequilibrium Green function approach. It is shown that the spin splitting of the dot level due to an external magnetic field leads to qualitatively new effects. In particular, numerical results show that the negative differential conductance and diode effect may occur in symmetrical junctions with non‐collinear magnetizations and for large enough magnetic polarization of the leads. It is also found that in asymmetrical junctions with one electrode being half‐metallic, the spin splitting gives rise to an enhancement of the diode‐like features in transport characteristics. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The influence of Fe layer thickness on electronic and magnetic properties of antiferromagnetically coupled Fe/Si multilayers
Authors: Luciński T. , Wandziuk P. , Baszyński J. , Szymański B. , Stobiecki F. , Zweck J.
Published: January 2006

The antiferromagnetically coupled Fe/Si multilayers deposited by magnetron sputtering with different Fe layer thicknesses have been examined. It has been shown that the magnetization of ferromagnetic layer reduces its value with decreasing Fe layers thickness affecting the antiferromagnetic interlayer coupling. This coupling has been found to occur for Fe layer thicker than 0.5 nm. It has been shown that the antiferromagnetic interlayer coupling occurs through the semiconducting spacer layer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic and transport properties of thin GdCo4B alloy films
Authors: Smardz L. , Toliński T. , Luciński T. , Gościańska I. , Szlaferek A. , Trybuła Z. , Kowalczyk A.
Published: January 2006

GdCo4B thin films were prepared onto liquid nitrogen (LN) cooled or non‐cooled glass substrates by an UHV flesh evaporation technique. Structural studies showed that the samples deposited onto the LN cooled or non‐cooled glass substrates are amorphous and crystallize after an UHV annealing at 873 K. The resistance of the amorphous thin films increases with temperature decreasing from RT down to 4.2 K, while the annealed samples exhibit metallic behaviour. The crystallization process was observed by resistivity measurements in the temperature range varied from RT to 873 K with a rate of 10 K/min. We have observed a systematic change in the shape and peaks position of the XPS valence band after in‐situ annealing of the “as prepared” amorphous GdCo4B thin films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetization and FMR studies of [Fe/Cr]n structures with ultrathin iron layers
Authors: Drovosekov A. B. , Kreines N. M. , Milyaev M. A. , Romashev L. N. , Ustinov V. V.
Published: January 2006

Magnetic multilayer structures [Fe(t Fe)/Cr(t Cr)]n with ultrathin (t Fe < 5 Å) iron layers prepared by a molecular beam epitaxy were studied using SQUID‐magnetometry and ferromagnetic resonance technique. For the samples with t Fe ≳ 3 Å, the obtained magnetization curves and resonance spectra are typical for regular magnetic superlattices. On the contrary, the samples with t Fe ≲ 3 Å demonstrate superparamagnetic‐like behavior. These samples show a strong temperature dependence of their static and resonance magnetic properties. To explain the obtained results, we propose a theoretical model considering a cluster structure of thin iron layers. Magnetization curves and resonance spectra are calculated using an effective field approximation taking into account an interlayer interaction and cluster size distribution. The calculated dependencies show a qualitative agreement with the experimental data. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties and 1H NMR spectroscopy of TM22+[WIV(CN)8]·nH2O
Authors: Kováč J. , Zentková M. , Bokor M. , Mihalik M. , Kavečanský V. , Mitróová Z. , Zentko A. , Pekker A. , Kamarás K.
Published: January 2006

We report on magnetic properties of bimetallic extended networks built from [WIV(CN)8]4– and TM2+ = Mn2+ , Fe2+, Co2+, Ni2+, Cu2+ , Zn2+. The weak exchange interaction is the reason for appearance of magnetically ordered state at low temperatures for all compounds with exception of Zn2[W(CN)8].nH2O. It has been shown that susceptibility data for all compounds, except Co2[W(CN)8].5H2O, follows the Curie Weiss law above T = 50 K. For Co2[W(CN)8].5H2O the modified Curie Weiss law is valid. Free induction decay (FID) signals showed behaviour peculiar to paramagnetic samples. The decayed more rapidly in a higher applied static magnetic field B 0 = ω 0/γ 1H. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)