Role of rare earth ion in spin glass behavior for R_0.7Sr_1.3MnO₄

Magnetic and structural properties for melt-grown single crystals of monolayered manganites R_0.7Sr_1.3MnO₄ (R = La, Pr, and Nd), possessing the K₂NiF₄ type structure, have been investigated. On the bases of magnetization, neutron powder diffraction, and relaxation measurements, it is revealed that all the three compounds display spin glass behaviors in the low-temperature region. In La_0.7Sr_1.3MnO₄, spin glass behaviors are observed isotropically both in the ab plane and along the c axis. In contrast, Pr_0.7Sr_1.3MnO₄ and Nd_0.7Sr_1.3MnO₄ show anisotropic spin glass transition. The salient feature of spin glass behavior found in the Pr- and Nd-doped compounds can be understood in terms of the enhanced lattice distortion induced by small rare earth ion as well as the magnetic anisotropy of the rare earth ions.