Magnetic spin interactions observed by heat capacity measurements for layered compounds: NaLnTiO_4 (Ln = Sm, Eu, Gd, Tb, Dy, Ho and Er)

摘要

Magnetic properties of a series of orthorhombic NaLnTiO_4 (Ln = Sm, Eu, Gd, Tb, Dy, Ho and Er) characterized by heat capacity measurements are reported. Magnetic transitions are observed for all NaLnTiO_4 investigated except for Ln = Eu. The change in magnetic entropy closely agrees with the expected theoretical values except for Ln = Sm and Gd. Peak profiles in temperature dependence of heat capacity indicate that Ln = Sm, Tb, Dy, Ho and Er phases possess Ising square lattices. Furthermore, Ln = Gd also exhibits the similar property regardless of its S state; there seems some,degree of anisotropy in its magnetic lattice. Magnetization and heat capacity data indicate that superexchange through oxygen is the dominant spin interaction in this system.