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 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.

Introduction : RKKY interaction Si 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

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) =

Motivation : How does the MR behave ? How does the MR behave in ferromagnet, CeRhSn2 ? (or in antiferromagnet, CeNiBi2) Magnetic phase diagram of CePd2Ga3 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

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)

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)

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

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

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) 224417

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

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

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.

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