Magnetic spin interactions observed by heat capacity measurements for layered compounds: NaLnTiO4 (Ln=Sm, Eu, Gd, Tb, Dy, Ho and Er)

Magnetic properties of a series of orthorhombic NaLnTiO4 (Ln=Sm, Eu, Gd, Tb, Dy, Ho and Er) characterized by heat capacity measurements are reported. Magnetic transitions are observed for all NaLnTiO4 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.