Magnetic-Field-Induced Sign Changes of Thermal Expansion in DyCrO₄

The anharmonicity of lattice vibration is mainly responsible for the coefficient of thermal expansion (CTE) of materials. External stimuli, such as magnetic and electric fields, thus cannot effectively change the CTE, much less the sign variation from positive to negative or vice versa. In this study, we report significant magnetic field effects on the CTE of zircon- and scheelite-type DyCrO₄ prepared at ambient and high pressures, respectively. At zero field, the zircon-type DyCrO₄ exhibits a negative CTE below the ferromagnetic-order temperature of 23 K. With increasing field up to ≥1.0 T, however, the sign of the CTE changes from negative to positive. In the scheelite phase, magnetic field can change the initially positive CTE to be negative with a field up to 2.0 T, and then a reentrant positive CTE is induced by enhanced fields ≥3.5 T. Both zircon and scheelite phases exhibit considerable magnetostrictive effects with the absolute values as high as ∼ 800 ppm at 2 K and 10 T. The strong spin–lattice coupling is discussed to understand the unprecedented sign changes of the CTE caused by applying magnetic fields. The current DyCrO₄ provides the first example of field-induced sign change of thermal expansion, opening up a way to readily control the thermal expansion beyond the conventional chemical substitution.