Ferromagnetism and Lattice Distortions in the Perovskite YTiO$_3$

TL;DR

This study investigates the thermodynamic properties of ferromagnetic YTiO₃, revealing how lattice distortions influence its magnetic behavior and how pressure affects its Curie temperature and spontaneous magnetization.

Contribution

It provides detailed experimental insights into the relationship between lattice distortions, magnetic properties, and pressure effects in YTiO₃, highlighting the role of GdFeO₃-type distortion and potential Jahn-Teller effects.

Findings

Ferromagnetism is strengthened by uniaxial pressure along the a-axis.

Thermal expansion shows magnetic contributions above T_C, unlike typical Heisenberg ferromagnets.

Pressure dependence indicates lattice distortions significantly influence magnetic properties.

Abstract

The thermodynamic properties of the ferromagnetic perovskite YTiO$_3$ 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 $T_C\simeq27$ K, are 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 $\mathbf{p}\parallel \mathbf{a}$ and is weakened by uniaxial pressures $\mathbf{p}\parallel \mathbf{b},\mathbf{c}$ 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 GdFeO$_3$-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.