Magnetic anisotropy in isovalent spin =7/2 family EuIn (=Ni, Pd, Pt)

Kaneko, Koji   ; Ikeda, Shugo*; Frontzek, M. D.*; Hanashima, Takayasu*; Nakao, Akiko*; Kiyanagi, Ryoji  ; Ohara, Takashi   ; Homma, Yoshiya*; Kobayashi, Hisao*; Yamagami, Hiroshi

Magnetism in rare-earth ions is accompanied by large orbital moment, and therefore, is influenced by single ion anisotropy via crystalline electric field. In contrast, Eu and Gd have unique state without orbital angular momentum J=S=7/2 with =0. It provides an ideal opportunity to study the effect of interactions and resulting collective spin behavior without single-ion anisotropy. Recently, interesting variation in the magnetic anisotropy is discovered in orthorhombic isovalent family EuTIn with T=Ni, Pd and Pt. Eu ions in all EuTIn have a stable divalent state across the series and therefore carries a large spin moment of S=7/2, whereas transition metal does not carry magnetic moment. Among these isovalent compounds, magnetic anisotropy have marked contrast as is not expected for spin system. EuNiIn has strong Ising-type magnetic anisotropy where b is a magnetic easy axis. In contrast, the anisotropy is changes into the a-b planar anisotropy in EuPdIn, and becomes the a-c planar type in EuPtIn, which is contrary to EuNiIn. In order to understand the mechanism of the magnetic anisotropy, single crystal neutron diffraction experiments were carried out. Despite strong neutron absorption of Eu and In, magnetic Bragg peaks were successfully observed. We will discuss the possible origin of the magnetic anisotropy in EuTIn based on the magnetic structure.