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Study of Magnetic Ordering
in YbPd
Reference
•R.Pott et al, Phys.Rev.Lett.54, 481-484 (1985)
Kazuki Kasano
Shimizu Group
2008 5.28 Wed M1 Colloquium
Contents
 Introduction
- Heavy fermion compounds （重い電子系化合物）
- Motivation
 Measurements
 Results
 Summary
 My study
2/13
3/13
Introduction
 Difference of specific heat
Normal metal
0
T2
γ : Electronic specific heat
AT2 : Lattice specific heat
CexLa1-xCu6
C/T (J/K2・mol)
C/T
C / T    AT
2
Heavy fermion compounds
log10T
Electronic specific heat is different
from normal metal !
三宅和正 著 「重い電子とは何か」 岩波書店
4/13
Introduction
 Electronic specific heat
Electronic specific heat is given by free electron model.
CElectronic  m  n
1
3
m : effective mass of electrons（電子の有効質量）
n : density of electrons（電子密度）
Electronic specific heat becomes large.
m becomes large.
= Heavy !!
5/13
Introduction
 Ce, Yb
Xe shell
Ce
2p6
3p6 3d10
4p6 4d10 4f1
5p6 5d1
(局在)
Localized or conduction
electron ?
n(r)
Ce
1s2
2s2
3s2
4s2
5s2
6s2
Conduction electrons
Part of 4f electrons are mixed with
conduction electrons !
RKKY interaction and Kondo effect
r/rB
n(r) : Distribution of electrons
rB : Bohr radius（ボーア半径）
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Introduction
 Two interactions
 Kondo effect
 RKKY interaction
Conduction electron’s spin
4f electron’s spin
Spin singlet state
(スピン一重項基底状態)
Kondo effect quenches spin !
(遮蔽する)
RKKY interaction makes
spin stable !
7/13
Introduction
 Competition
In Ce and Yb compounds...
At high temperature,
At low temperature(～10 K),
there is no magnetic ordering.
magnetic ordering occurs.
Kondo effect is dominant.
RKKY interaction is dominant.
Competition !
(競合)
8/13
Introduction
 Motivation
Ce compounds
Magnetic ordering has been found frequently.
Yb compounds
There had been few magnetic ordering.
YbPd, Yb3Pd4, YbIr2
Measurements
 Specific heat
(T = 1.5 ～ 300 K)
 Thermal expansion
(T = 1.5 ～ 300 K)
 Electrical resistivity
(T = 40 mK ～ 300 K)
 Magnetic susceptibility
(T = 40 mK ～ 300 K, H = 1.72 mGauss)
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Results
 Specific heat and thermal expansion
T(K)
•Specific heat is larger than LuPd.
•Some anomalies are found.
125K
105K
1.9K
α(10-6K-1)
C(J/mol・K)
T(K)
Δα(10-6K-1)
1.9K
ΔC(J/mol・K)
125K
105K
T(K)
•These anomalies are structural.
•They are found at the same
temperatures the case of
specific heat.
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Results
1.9K
0.5K
T(K)
•Electrical resistivity is larger
than LuPd.
•At 0.5 K, a new anomaly is found.
χ(emu/mol)
ρ(10-6Ωcm)
 Electrical resistivity and magnetic susceptibility
H =1.72(mGauss)
0.5K
T(K)
•About under 2 K ,
the magnetic ordering occurs.
•A hysteresis is found at 0.5 K.
Summary
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YbPd
At high temperature
• Kondo effect is dominant and there is no magnetic ordering.
• Two structural phase transitions are found at 125 , 105 K.
At low temperature
• RKKY interaction overcomes Kondo effect
and magnetic ordering occurs at about 2 K .
• Magnetic phase transition is found at 0.5 K.
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My study
YbPd
Kondo effect
RKKY interaction
Competition
Pressure
What happen...?
Appendix
 Effective mass
In vacuum
In crystal
m*
Electron
Force
Interaction
with lattice
m  9.1101031 kg
m changes !
This is effective mass.
Appendix
 Doniach phase diagram
1
)
J cf Dc ( F )
kBT
k BTK  exp(
kBTRKKY  J cf2 Dc ( F )
JcfDc(εF)
Jcf : c-f Exchange interaction
Dc(εF) : Density of state at Fermi energy
Appendix
 Calculation of valence
Valence
（価数）
T(K)
Anomalies at 125K and 105K should be structural.
They falsify the valence determination with the volume anomaly.
As a result, YbPd become mixed-valent state.
(Valence changes 2.82 at 300K to 2.80 near 0K)

Sb-NQR probe for superconducting properties in the