Magnetic phase diagram, magnetoelastic coupling, and Grüneisen scaling in CoTiO₃

High-quality single crystals of CoTiO₃ 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¯3) phase. At the antiferromagnetic ordering temperature T_N pronounced λ-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_N than pressure applied in-plane. The hydrostatic pressure dependency derived by means of Grüneisen analysis amounts to ∂T_N/∂ p ≈ 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 CoTiO₃. 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 TN as well as in the long-range magnetically ordered phase.