Ferromagnetism and Lattice Distortions in the Perovskite YTiO$_3$

W. Knafo; C. Meingast; H. v. Löhneysen; A. V. Boris; P. Popovich; N. N. Kovaleva; P. Yordanov; A. Maljuk; R. K. Kremer; B. Keimer

doi:10.1103/physrevb.79.054431

arXiv · 0812.1533

Ferromagnetism and Lattice Distortions in the Perovskite YTiO$_3$

W. Knafo·C. Meingast·H. v. Löhneysen·A. V. Boris·P. Popovich·N. N. Kovaleva·P. Yordanov·A. Maljuk·R. K. Kremer·B. Keimer

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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.

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W. Knafo, C. Meingast, H. v. Löhneysen, A. V. Boris, P. Popovich, N. N. Kovaleva, P. Yordanov, A. Maljuk, R. K. Kremer, B. Keimer. 2008-12-08. Ferromagnetism and Lattice Distortions in the Perovskite YTiO$_3$. https://doi.org/10.1103/physrevb.79.054431

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