Abstract
The thermodynamic properties of the ferromagnetic perovskite 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 , is consistent with a three-dimensional Heisenberg model of ferromagnetism. However, a magnetic contribution to the thermal expansion persists well above , which contrasts with typical three-dimensional Heisenberg ferromagnets, as shown by a comparison with the corresponding model system EuS. The pressure dependences of and of the spontaneous moment are extracted using thermodynamic relationships. They indicate that ferromagnetism is strengthened by uniaxial pressures and is weakened by uniaxial pressures and hydrostatic pressure. Our results show that the distortion along the and axes is further increased by the magnetic transition, confirming that ferromagnetism is favored by a large -type distortion. The -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.
6 More- Received 8 December 2008
DOI:https://doi.org/10.1103/PhysRevB.79.054431
©2009 American Physical Society