Ferromagnetism and lattice distortions in the perovskite YTiO3

The thermodynamic properties of the ferromagnetic perovskite YTiO3 are investigated by thermal expansion, magnetostriction, specific-heat, and magnetization measurements. The low-temperature spin-wave contribution to the specific heat, as well as an Arrott plot of the magnetization in the vicinity of the Curie temperature T-C similar or equal to 27 K, is consistent with a three-dimensional Heisenberg model of ferromagnetism. However, a magnetic contribution to the thermal expansion persists well above T-C, which contrasts with typical three-dimensional Heisenberg ferromagnets, as shown by a comparison with the corresponding model system EuS. The pressure dependences of T-C and of the spontaneous moment M-s are extracted using thermodynamic relationships. They indicate that ferromagnetism is strengthened by uniaxial pressures p parallel to a and is weakened by uniaxial pressures p parallel to b, c and hydrostatic pressure. Our results show that the distortion along the a and b axes is further increased by the magnetic transition, confirming that ferromagnetism is favored by a large GdFeO3-type distortion. The c-axis results, however, do not fit into this simple picture, which may be explained by an additional magnetoelastic effect, possibly related to a Jahn-Teller distortion.