IMSS Symposium, 16-17 October 2008

High Resolution Inelastic Neutron
Scattering Studies on Spin Systems

Shinichi Itoh
Neutron Science Division
Institute of Materials Structure Science
High Energy Accelerator Research Organization

High Resolution Chopper Spectrometer at J-PARC
Energy Transfer E (meV)This spectrometer is useful for a wide range ofdynamical studies of materials with high resolutions.

Current status of construction

spin waves

Dec 2008
Oct 2009

water

Molecular
spectroscopy

Momentum Transfer Q (Å-1 )Completion of building Shieldings
Test experiment using KENS instrument.
Experiment using full vacuum chamber + low angle detsHigh Resolution Experiments (ΔE/Ei ~ 1%)
using relatively high energy neutrons (Ei ~ 0.1 - 1 eV)
for studies on spin systems
1. High resolution experiments in conventional (Q,ω) space
Ei=100meV, ΔE=1meV, ΔQ=0.03A-1
Quantum phase transition and multi degree of freedom incorrelated electron systems
2. Access to 1st Brillouin zone with low angle and high Ei
E=10meV, Q=0.2A-1
Observation of ferromagnetic spin waves from polycrystalline
sample and material development
3. Possibility of eV region neutron spectroscopy
Ei=1eV, ΔE=10meV, ΔQ=0.1A-1
Observations of high energy magnetic excitations
as well as electronic excitations

1. High resolution experiments in conventional (Q,ω) space
Experience: S dependent quantum renormalization in 1D AFM
S=1/2, CuCl2・
2NC5D5E(q)= 2πJ | sin q|= 4SJR | sin q |R = π/2
E(q) Y. Endoh et al. 1974
χ(T) K. Takeda et al. 1971

χ(T)S=3/2,CsVCl3

E(q)= 4SJR | sin q |J ?, R ?
E(q) S. Itoh et al. 1995
χ(T) M. Niel et al. 1977

1. High resolution experiments in conventional (Q,ω) space
Experience: S dependent quantum renormalization in 1D AFM
S=1 CsNiCl3

S=3/2 CsVCl38CsVCl3100(a) T = 6 K(c) T = 40 K(e) T = 20 K

80

6E (meV)

S=2 CsCrCl3
40

30

60
4

20
40

21020

INC
0
0.0

0.1

0.2

0.3

0.4

0.5

MARI

00.00.1

q (rlu)

0.2

0.3

0.4

INC
0.5

00.00.1

q (rlu)

0.5

0.2

0.3

0.4

0.5

q (rlu)0.2(f)(d)(b)

classical : h" = 4SJ sin aq
quantum : h" = 4SRJ sin aq! (rlu)

0.4

0.1
0.2
0.1

INC0.0!

S(q, " ) = S(q)F(q, " )#F(q, " ) =(" $ Eq )2 + # 2
S(q) = % S(q, " )d" =1q 2 + & (T , J )2

0.1

0.3

01020T (K)30

PRISMA40

0.0050100 150 200 250

T (K)PRISMA
0.0040

80

120

T (K)

S. Itoh et al., PRL 74 (1995) 2374 / JPSJ 73 (2004) 269.

Ei=125meV, ΔE/Ei=3%, Δq=ki(ΔE/Ei)/2=0.12Å-1→ high resolutions are indispensable to reach theresult with a single shot of experiment1. High resolution experiments in conventional (Q,ω) space
Random Singlet Phase Transition
S=1/2
By the distribution ofexchange constant J,randomly selected spin pair iscoupled into singlet (randomsinglet phase).

S=3/2
δ : Distribution of J
δ > δc(Seff=3/2)
δ < δc (Seff=1/2)
Phase transition between two phases at δ = δc .
S(q,w) shows critical exponent ψ near δc.

S=1/2 BaCu2(Si0.5Ge0.5)2O7
T. Masuda et al. PRL 93 (2004) 077206

S=3/2 CsV(ClcX1-c)3, X=Br, ICsVC3

S(q," ) =AF (qln 2 (#0 /" ))3" ln (#0 /" )S(q," ) =

1/ 2
A1/#%
qln($/")/n00" ln1+1/# ($0 /" )()

1. High resolution experiments in conventional (Q,ω) space
Dynamics of holes doped into Haldane chain- Determination of entire dispersion relation of 1D chain- Doping dependence of incommensurate low-E excitations⇨ Comprehensive understanding of hole dynamics

1. High resolution experiments in conventional (Q,ω) space
Possibility of observation of orbital waves in YVO3Szz
YVO3, V3+ 3d2 t2g2

J0 = 4t02/(U’ – I) = 33 meV
4 modesyA (dxy→ dyz) and zA (dzx → dyz)
at site A (dxy and dzxoccupied),xB (dxy → dzx) and zB (dyz → dzx)
at site B (dxy and dyz occupied).
S. Ishihara: Phys. Rev. B 69 (2004) 075118, C. Ulrich et al.: Phys. Rev. Lett. 91(2003) 257202.

2. Access to 1st Brillouin zone with low angle and high Ei
Observation of spin waves from polycrystalline sample

Single crystal sample

polycrystalline sample2. Access to 1st Brillouin zone with low angle and high Ei
Metal Ferromagnet SrRuO3 cubic perovskite, Tc = 160 K
E(meV)

40

Ei=0.2eV
T = 165K

30! (meV)

Ei=0.2eV
T = 10 K

10Ei = 0.5 eV
T = 165 K
critical scattering
22
S(Q," ) ~ 1/(" +!(Q) )2.5! (Q) = AQ
2.5
A = 42.4 ± 5.3 meVA

20

100
0.0

0

0.2

0.4

0.6

0.8

-1

0.2

Q (A-1)

0.8

0.2

Q (A-1)

0.8

Q (A )30

E (meV)

SrRuO3
T = 10 K
25 phi ! 0.7°
Ei = 0.5 eV
Ei = 0.2 eV

Ei=0.5eV
phi=3°MARI/MAPS

20

J=1.7meV

15J=0.7meV→ Egap ˜ several meV

J=1.7meV (Tc = 8J)

10High symmetry FM：Egap ˜ 0Suggestion of contribution of orbitals

J=0.7meV (D=A)

500.0

Ei=50meV
phi=5°3-axis

0.2

0.4

0.6-1Q (A )Magnetic excitation at E=10meV, Q=0.2Å-1
Γ(Q),Tc → J=0.7˜1.7meV

0.8

1.01.02. Access to 1st Brillouin zone with low angle and high Ei
Ferromagnetic SemiconductorsFerromagnetic semiconductors @RT: indispensable for spintronics
Do room temperature
ferromagnetic
semiconductors reallyexist?
What is the mechanismof ferromagnetism, if thematerials exist?

2. Access to 1st Brillouin zone with low angle and high Ei
Ferromagnetic Semiconductors
Possible mechanisms of ferromagnetism in semiconductors
1. carrier induced interaction

2. double exchange interaction

high carrier density: FM low carrier density: PM

insulator:AFM

Carriers (holes) mediates FM interaction.

parallel spins hopping by hole-doping:
FMShort range interaction: dispersive spin waves

long range interaction: flat spin waves

Determination of mechanism by measuring spin wave dispersion
Almost samples are thin films. We are looking for bulk samples
for demonstrations of inelastic neutron experiments.

3. Possibility of eV region neutron spectroscopy
High Energy Magnetic Excitations in CrINC
KENS

HET
ISIS

3axis
JRR-3

3. Possibility of eV region neutron spectroscopy
Electronic excitations

Sr2CuO3 ARPES[Ni(chxn)2Br]Br2

ECT=2eV

ECT=1.2eV ARPES

Clear spin-charge separation
Sr2CuO3SrCuO2[Ni(chxn)2Br]Br2

unclear spin-charge separation

H. Fujisawa et al., PRB 59 (1999) 7358.
C. Kim et al., PRL 77 (1996) 4054.
S. Fujimori et al., PRL 88 (2002) 247601.

ECT decreases via perturbationof V(inter-site Coulomb).

The theoretical calculation wellagrees with the result of ARPES.

3. Possibility of eV region neutron spectroscopy
Electronic excitations
1eV →[Ni(chxn)2Br]Br2

Novel magnetic
excitations

1D extend Hubberd model
N. Tomita and K. Nasu, Phys. Rev. B 61 (2000) 2488

1/10 of magnons
More 1/10 by F(Q)2

J-PARC 1MW
Ei = 1 eV, ΔE/Ei = 1%
N = 100, ΔN/N = 10%

Magnetic excitation energies become
the same order as charge excitationenergies via inter-site Coulomb
repulsion.
Spin-induced charge excitations canbe observed as magnetic scattering.

400 g days = 40g x 10days similar experiment to current high-Tc studies
at ISISHigh Resolution Experiments (ΔE/Ei ~ 1%)
using relatively high energy neutrons (Ei ~ 0.1 - 1 eV)
for studies on spin systems
1. High resolution experiments in conventional (Q,ω) space
Ei=100meV, ΔE=1meV, ΔQ=0.03A-1
Quantum phase transition and multi degree of freedom incorrelated electron systems
2. Access to 1st Brillouin zone with low angle and high Ei
E=10meV, Q=0.2A-1
Observation of ferromagnetic spin waves from polycrystalline
sample and material development
3. Possibility of eV region neutron spectroscopy
Ei=1eV, ΔE=10meV, ΔQ=0.1A-1
Observations of high energy magnetic excitations
as well as electronic excitations