1. Magnetic transition in the Kondo lattice system CeRhSn2
SHIMIZU Group KANEMASA Taisuke
Z. Hossain et al., J.Phys.: Condens. Matter 14 (2002) 96879

2. Contents Introduction
:The property of Ce-compound and magnetoresistance
Experiment
:The measurement of electrical resistivity,
magnetization, and magnetoresistance of CeRhSn2
Discussion
Summary

3. Introduction : magnetism of Ce-compounds
competition
RKKY interaction
Indirect interaction between 4f electrons
Kondo effect
interaction between 4f and conduction electron 4f
conduction 4f 4f
conduction e- e-
Quenches the magnetic moments of 4f electron
Causes a long-range magnetic order P
The relation of Kondo effect and RKKY interaction.

4. Introduction : RKKY interactionSi Sj
Ferromagnetic Ce-compound is rare.
Ri,j
CeAgSb2
Pressure induced ferro-antiferromagnetic transition
Hi,j　∝ －J (Ri,j) ・Si・Sj
J > 0 → Si・Sj > 0
ferromagnetism
J < 0 → Si・Sj < 0
antiferromagnetism
To examine the property 　　　of magnetism…
　・Magnetization M 磁化
　・Magnetic susceptibility χ 磁化率
　・Specific heat C
　・Magnetoresistance (MR)　
　　磁気抵抗効果 P

5. Introduction : magnetoresistance
Lanthanides
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Magnetoresistance
The magnetic field dependence of the electrical resistivity
4f 　0 　1 　2 　3 ・・・
The magnetoresistance of LaCu6 at various temperatures
Electrical resistivity
ρ = ρ0 + ρph + ρmag　+ ・・・　　　　　(Matthiessen’s rule)
　　ρ0 : the residual resistivity
　　ρph : phonon scattering
　　ρmag : spin scattering
magnetic field acts
ρ (H) – ρ(0)　ρ (0)
Δρ/ρ (0) =

6. Motivation : How does the MR behave ?
How does the MR behave in ferromagnet, CeRhSn2 ?
(or in antiferromagnet, CeNiBi2)
Magnetic phase diagram of CePd2Ga T. Burghardt et al., J.Phys.: Condens. Matter 17 (2005) 871
TC = 6.3 K
I’ll consider the sample I study, CePd2Ga3
Pressure induced ferro-antiferromagnetic
transition at ~ 2.3 GPa FM
AFM
The magnetization
measurement under
high pressure is difficult.
Ferromagnetic Ce-
compound is rare.
specific heat C, resistivity ρ, 　 DC and AC magnetic susceptibility χ
MR measurement of CePd2Ga3
CeRhSn2 is the object to compare with CePd2Ga3

7. Properties of CeRhSn2 and CePd2Ga3
Ferromagetic compound TC = 4.0 K
・ Two inequivalent Ce sites Sn Rh 2 2 2
Ferromagetic compound TC = 6.3 K Pd 1 1 1 Ga
easy
axis Ce c
Crystal structure of CeRhSn2 (Cmcm) D. Niepmann et al., Chem. Mater. 11 (1999) 1597
Crystal structure of CePd2Ga3 (P6lmmm)

8. Experiment in CeRhSn2 TC TC ρmag = ρ (CeRhSn2) -ρ(LaRhSn2)
●The drop at 4 K indicates ferromagnetic transition.
●The minimum by Kondo effect at ~ 20 K a ρ ∝ - logT
●The inset shows the magnetic part of the resistivity (ρmag). TC TC
The temperature dependence of the electrical resistivity of CeRhSn2
ρmag = ρ (CeRhSn2) -ρ(LaRhSn2)

9. The magnetization at B ~ 0.2 T. at 5 T. ①M increases rapidly
②M didn’t reach saturation
at 5 T.
①The movement of magnetic domains
②The rotation of magnetization
Magnetization as a function of field at 2 and 10 K B

10. The field dependence of the resistivity of CeRhSn2
MR totally negative
・Initial rapid decrease
・The broad maximum indicates a complicated magnetic order.
The magnetoresistance of CeRhSn2

11. The magnetization and magnetoresistivity of antiferromagnet, CeNiBi2 (TN = 6 K)
・M gradually increase.
・The inflection point at 5 T.
MR positive　 negative
Enhancement of spin-disorder scattering
Field-induced ferromagnetic state !
The magnetization as a function of field at 1.5 K
The magnetoresistance at various temperatures
A. P. Pikul et al., Phys. Rev. B 67 (2003)

12. Discussion 1 Antiferromagnetic compounds Ferromagnetic compounds
The MR is initially positive and
turns negative at higher fields.
The MR is totally negative.
positive
negative
positive
negative B B

13. Comparison of magnetoresistance
・ P ≦ 1.9 GPa, the MR was wholly negative.
Para 6
Tm(K) FM
AFM
2.3 5
P (GPa)
The MR changed remarkably at 2.1 GPa
CePd2Ga3
The magnetoresistance at various pressures and ~ 0.12 K
The magnetoresistance at 1.9 and 2.1 GPa

14. Discussion 2 P ≦ 1.9 GPa Ferromagnetic behavior P ＝ 2.1 GPa
≦1.5 T ferromagnetic-like behavior
≧1.5 T antiferromagnetic-like behavior
The magnetoresistance at ~ 0.12 K
CePd2Ga3
The possibility of the pressure-induced
ferro-antiferromagnetic transition.

15. In CeRhSn2 Summary The ferromagnetic transition occurs at ~ 4.0 K
The MR is wholly negative.