The Crystal Electric Field Effect on 4f-Hole and Magnetic Phase Diagram in Heavy-Fermion Compound YbPtGe Determined from Ultrasonic Measurements

• Published in: Journal of the Physical Society of Japan Vol. 84; no. 12; p. 1
• Main Authors: Xi, Xiaojuan, Ishii, Isao, Noguchi, Yoshihito, Goto, Hiroki, Kamikawa, Shuhei, Araki, Koji, Katoh, Kenichi, Suzuki, Takashi
• Format: Journal Article
• Language: English
• Published: Tokyo The Physical Society of Japan 15-12-2015
• Subjects: Anisotropy; Crystal structure; Elastic modulus; Electric fields; Ferromagnetism; Fittings; Hardening; Measurement; Modulus of elasticity; Phase diagrams; Softening; Temperature effects
• ISSN: 0031-9015; 1347-4073
• DOI: 10.7566/jpsj.84.124602

YbPtGe with the orthorhombic e-TiNiSi-type structure is reported as a heavy-fermion ferromagnet with the magnetic transition temperature TC = 5.4 K. Recent research suggested that its magnetic anisotropy can be ascribed to the crystal electric field (CEF) effect. In order to clarify the CEF effect and to investigate the magnetic phase transition in this compound, ultrasonic measurements of YbPtGe and related theoretical calculation have been performed. The transverse elastic moduli C44, C55, and C66 exhibit a softening characteristic with a peak around 150 K while the longitudinal moduli C11, C22, and C33 show a continuous hardening in the temperature (T) range above TC. Theoretical strain-susceptibility fitting indicates that the softening results from a quadrupole interaction between the ground and excited Kramers doublets of CEF. For the elastic moduli below TC, abrupt elastic hardening is observed in C22, C33, and C55 while C11, C44, and C66 exhibit a step-like softening. The difference between the softening and hardening of elastic moduli below TC may be due to the magnetostriction or a different dominant coupling between a strain and an order parameter. Phase diagram with a magnetic field (H) parallel to the a-axis is obtained by the measurements of the T and H dependences of the elastic modulus C11.