Magnetic transition in the Kondo lattice system

CeRhSn2

SHIMIZU Group

KANEMASA Taisuke

Z. Hossain et al., J.Phys.: Condens. Matter 14 (2002) 96879

Contents

Introduction :The property of Ce-compound and magnetoresistance Experiment :The measurement of electrical resistivity, magnetization, and magnetoresistance of CeRhSn2

Discussion

Summary

Introduction : magnetism of Ce-compounds

Ce-compounds

The relation of Kondo

effect and RKKY interaction.

RKKY interaction

Indirect interaction between 4f electrons

e-

4f 4f

competition Kondo effect

interaction between 4f and conduction electron

4f conduction

conduction

e-

Causes a long-range magnetic order

Quenches the magnetic moments of 4f electron

P

Hi,j 　∝ － J (Ri,j) ・ Si ・ Sj

J > 0 → Si ・ Sj > 0 ferromagnetism J < 0 → Si ・ Sj < 0 antiferromagnetism

Ri,j

Si Sj Ferromagnetic Ce-compound is rare.

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

Introduction : RKKY interaction

P

CeAgSb2

Pressure induced ferro-antiferromagnetic transition

Lanthanides

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Introduction : magnetoresistance

Magnetoresistance The magnetic field dependence

of the electrical resistivity

Electrical resistivity

ρ = ρ 0 + ρph + ρmag 　 + ・・・　　

　　　 (Matthiessen’s rule)

　　 ρ0 : the residual resistivity

　　 ρph : phonon scattering

　　 ρmag : spin scattering magnetic field acts Δρ/ ρ (0) =

The magnetoresistance of LaCu6 at various temperatures

4f 　 0 　 1 　 2 　 3 ・・・

ρ (H) – ρ(0) ρ (0)

I’ll consider the sample I study, CePd2Ga3

Pressure induced ferro-antiferromagnetic transition at ~ 2.3 GPa

Motivation : How does the MR behave ?

How does the MR behave in ferromagnet, CeRhSn2 ?

(or in antiferromagnet, CeNiBi2)

specific heat C, resistivity ρ, 　 DC and AC magnetic susceptibility χ

Magnetic phase diagram of CePd2Ga3

T. Burghardt et al., J.Phys.: Condens. Matter 17 (2005) 871

FM

AFM

Ferromagnetic Ce-compound is rare.

The magnetizationmeasurement under high pressure is difficult.

MR measurement of CePd2Ga3

CeRhSn2 is the object to compare with CePd2Ga3

TC = 6.3 K

Properties of CeRhSn2 and CePd2Ga3

GaCe

Pd

Crystal structure of CeRhSn2 (Cmcm) D. Niepmann et al., Chem. Mater. 11 (1999) 1597

Crystal structure of CePd2Ga3 (P6lmmm)

Ferromagetic compound TC = 4.0 K

・ Two inequivalent Ce sites

Ferromagetic compound TC = 6.3 K

111

2 22

Ce

Rh

Sn

easyaxis

c

Experiment in CeRhSn2

The temperature dependence of the electrical resistivity of CeRhSn2

TC

TC

●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).

ρmag = ρ (CeRhSn2) -ρ(LaRhSn2)

The magnetization

①M increases rapidly at B ~ 0.2 T. 　

Magnetization as a function of field at 2 and 10 K

②M didn’t reach saturation at 5 T.

①The movement of magnetic domains

B

②The rotation of magnetization

The field dependence of the resistivity of CeRhSn2

The magnetoresistance of CeRhSn2

・ Initial rapid decrease

・ The broad maximum indicates a complicated magnetic order.

MR totally

negative

The magnetization and magnetoresistivity of antiferromagnet, CeNiBi2 (TN = 6 K)

The magnetoresistance at various temperatures

Field-induced ferromagnetic state !

MR positive 　

negative

A. P. Pikul et al., Phys. Rev. B 67 (2003) 224417

The magnetization as a function of field at 1.5 K

・ M gradually increase.

・ The inflection point at 5 T.

Enhancement of spin-disorder scattering

Discussion 1

Ferromagnetic compounds Antiferromagnetic compounds

B

positive

negative

B

positive

negative

The MR is totally negative. The MR is initially positive and turns negative at higher fields.

Comparison of magnetoresistance

0 2 4 6 8

- 0.8

- 0.6

- 0.4

- 0.2

0.0

0.2

- 0T

(

cm)

B (T)

1.4 GPa

1.0 GPa

0.2 GPa

1.9 GPa

2.1 GPa

0 2 4 6 8

0

2

4

6

8

10

-

0T (

cm

)

B (T)

1.9 GPa

2.1 GPa

The magnetoresistance at various pressures and ~ 0.12 K The magnetoresistance at 1.9 and 2.1 GPa

CePd2Ga3

・ P ≦ 1.9 GPa, the MR was wholly negative.

FMFMAFMAFM

ParaPara

PP (GPa) (GPa)2.3

Tm

(K)

0

6

5

The MR changed remarkably at 2.1 GPa

Discussion 2

0 2 4 6 8

- 0.8

- 0.6

- 0.4

- 0.2

0.0

0.2

- 0T

(

cm)

B (T)

1.4 GPa

1.0 GPa

0.2 GPa

1.9 GPa

2.1 GPa

The magnetoresistance at ~ 0.12 K P ≦ 1.9 GPa

Ferromagnetic behavior

P ＝ 2.1 GPa

≦1.5 T ferromagnetic-like behavior

≧1.5 T antiferromagnetic-like behavior

The possibility of the pressure-induced

ferro-antiferromagnetic transition.

CePd2Ga3

Summary

In CeRhSn2

The ferromagnetic transition occurs at ~ 4.0 K

The MR is wholly negative.