Magnetic phase diagram, magnetoelastic coupling and Grüneisen scaling in CoTiO${}_3$

Abstract

High-quality single crystals of CoTiO${}_3$ are grown and used to elucidate in detail structural and magnetostructural effects by means of high-resolution capacitance dilatometry studies in fields up to 15 T which are complemented by specific heat and magnetization measurements. In addition, we refine the single-crystal structure of the ilmenite ($R\bar{3}$) phase. At the antiferromagnetic ordering temperature $T_{\mathrm{N}}$, pronounced $\hat{I}»$-shaped anomaly in the thermal expansion coefficients signals shrinking of both the $c$ and $b$ axes, indicating strong magnetoelastic coupling with uniaxial pressure along $c$ yielding six times larger effect on $T_{\mathrm{N}}$ than the pressure applied in-plane. The hydrostatic pressure dependency derived by means of Grüneisen analysis amounts to $\partial T_{\mathrm{N}}/\partial p\approx 2.7(4)$~K/GPa. The high-field magnetization studies in static and pulsed magnetic fields up to 60~T along with high-field thermal expansion measurements facilitate in constructing the complete anisotropic magnetic phase diagram of CoTiO${}_3$. While the results confirm the presence of significant magnetodielectric coupling, our data show that magnetism drives the observed structural, dielectric, and magnetic changes both in the short-range ordered regime well-above $T_{\mathrm{N}}$ as well as in the long-range magnetically ordered phase.

Accepted for publication in PRB