dynamics of novel molecular magnets v-ring and rare earth compounds
DESCRIPTION
Dynamics of novel molecular magnets V-ring and rare earth compounds. Okayama Univ. H. Nojiri. Introduction Magnetization step in V-rectangular ring Short range correlation effect in molecular magnet Rare earth compounds Summary. Collaborators. Okayama Univ. T. Taniguchi and K. Aikawa - PowerPoint PPT PresentationTRANSCRIPT
Dynamics of novel molecular magnetsV-ring and rare earth compounds
Okayama Univ. H. Nojiri
Introduction
Magnetization step in V-rectangular ring
Short range correlation effect in molecular magnet
Rare earth compounds
Summary
Collaborators
Okayama Univ.
T. Taniguchi and K. Aikawa
Ames Lab., Iowa State Univ.
M. Luban, P. Kögerler
Res. Lab. of Resources Utilization, TITEC
T. Yamase E. Ishikawa
Correlates system and isolated systemCs3Cr2X9:3D coupled dimer
Y. Ajiro, Y. Inagaki et al.
French-Japanese Symposium, Paris 2003
T
H
?
How intra-molecular correlation
is established?
H
H
E
M
E
H
HM
?Crossover
Thermal populationShort range orderSize dependence
T<<J T>>J
High Magnetic Fields in Okayama40 T Single shot pulsed fields
Temperature 0.4-400 KESR 35 GHz-7 THz
30 T Repeating pulsed fields30 T Portable pulsed field
– Complex pulsed field– X-ray, Free Electron Laser
Antiferromagnetic four spin ring:V12
Large rectangle S=1/2(V4+)Small rectangle Mixed valence non-magnetic Effective S=2 below R.T.
(NHEt3)4[VIV8VV
4As8O40H2O]H2O
N.S.=24
Neutron scattering and energy structure
Basler et al. Inorg. Chem. 41(2002)5675
S=0
S=1
S=1
S=2
Two triplets
Small splitting by exchange anisotropy
Magnetization process V12:two major steps
Two major step for
S =0 to S=1
S =1 to S=2
Intermediate step at 20 T
Small step of ~4 % of full moment
Splitting of large step Each major step splits into two steps
No orientation dependence, small g-anisotropy
Splitting of lowest excited states,
contradicts to neutron result
Step is a very useful means for study of energy level
Temperature dependence of large step
Large hysteresis in 4.2 K~1.5 K Second step in down sweep
No hysteresis in low temperature
Hysteresis with thermal effect
Magnetic Fohen effect ?E
H
Intermediate step
No level crossing point at ground state Relaxation in excited state Non-adiabatic transition?
Sweep velocity~20000 T/s at 10 T
Non adiabatic transition
Sweep velocity ~20000 T/s at 10 T p~0 for infinite v E=0.1 K, v~108 T/s E=3 K, v~105 T/s
Is such large gap is reasonable?
( ) ⎥⎦
⎤⎢⎣
⎡ −−= −12
2exp1 vEp
hπ
E
HE
Small steps
4 % of magnetization by isomatic cluster Defect driven signal Contribution of mixed valence phase NMR-T1, T-dependence
Two gaps Large and Small gaps F. Borsa et al. private communication
Temperature dependence of EPR
Small splitting for center peak
-splitting of lowest triplet
Large splitting for side peaks
- higher excited state signals
ESR spectra with short range correlation
T>J Classical regimeconventional paramagnetic resonance
T<J Short range ordercorrelation:~1/T
T< TN Antiferromagnetic order
infinite divergence of
kBT~J
T
Temperature dependence of EPR
Width is nearly temperature independent
Small shift at low temperature
Short range regime is not clear
S=2 to S=0 S=2 to S=1
Field dependence of EPR
Drastic change at steps
At higher fields, where S=2 or 1 is ground state
higher temperature, splitting is observed
low temperature, splitting is averaged
Domination of S=2 ground state
Crossover in infinite chain system
S=1 antiferromagnetic chain
Spiral structure
Formation of Haldan gap at low-T
PbNi2V2O8Uchiyama, Masuda, Uchinokura
N.S.=
Crossover from EPR to triplet resonanceAt high-T EPR split for single ion D
At low-T, Triplet split by effective DTemperature dependence of D
as evolution of quantum ground state
Wide regime of short range order
T. Masuda, K. Uchinokura and H.N.
H
E
Hp =DSz2 +gμBSi ⋅H
Hh = JSiSi+1 +DSiz2 +gμBSi ⋅H( )
i∑
Ht =D'Sz2 +gμBSi ⋅H
EPR of Spin ball V18-N3
Spherical cluster of V4+/V 5 + ions
15 of S=1/2 spins
Strong antiferromagnetic coupling
~5 B at 30 T
K. Aikawa, H.N. and T. Yamase
N.S.=215
EPR of Spin ball V18-N3
Shift of line width below 50 K
Saturation below 3 K
Ground state becomes stable
Short range regime below 20 K
Different from V12
Spin ball and ring (1)Variety of shape and network(2)Topology not available in regular lattice
fine particle 、 atomic spacing no-magic number as C60
(3)Number of state SN replace S=1/2 to S=5/2(4)Common energy structure Mo72Fe30:icosidodecahedron
N.S.=630
ESR of Mo72 Fe30
Increase of line width
Shift of resonance field
Development of short range correlation
Broad line width
Fe3+:not single ion relaxation
Frustration
Finite size effect
Decrease of line width at low T
No-magnetic ordering
but Saturation of correlation length
Rare earth compound Rare Earth compound
Longer spin
Larger magnetization
Easy substitution of ions
Smaller exchange coupling
Na8H18[{Er3O(OH3)(H2O)3}2
Al2(Nb6O19)5]40.5 H2O
Coupled triangles of Er
Magnetization of Er6 Saturate around 2 T Finite slope for anisotropyHysteresis at low fields similar to V15
Na8H18[{Er3O(OH3)(H2O)3}2
Al2(Nb6O19)5]40.5 H2O
Summary(1)Dynamics of V-ringMagnetization is very sensitive and precise probe
of energy level and dynamics
(2)Dynamical crossover and short range correlation
For large-N system, a clear short range order and possibly a quasi order
correlation length>size
(3)Rare earth compound
new candidate of single molecular magnet
1023
101
1015
104
SQUIDMolecule
Atom
630
215
24