Heat Capacity and magnetocaloric effect in the Zircon and Scheelite phases of RCrO4, R = Tb, Er, Ho

 

We present here new magnetization and heat capacity data under magnetic field and direct measurements of the magnetocaloric effect (MCE) in the zircon and the new scheelite phases of RCrO₄ (R ​= ​Tb, Er, Ho) from 5 ​K to 100 ​K, for magnetic fields B from 0 to 9 ​T. Zircons have a high MCE near their Curie point, T_C ​≃ ​20 ​K, reaching maximum isothermal entropy increments, |ΔS_T| ​= ​21, 19.4, and 16.2 ​J ​kg⁻¹K⁻¹ for HoCrO₄, ErCrO₄, and TbCrO₄, respectively, for an external field of 5 ​T. TbCrO₄ has another anomaly near T_D ​= ​60 ​K associated to a Jahn-Teller transition from the tetragonal zircon structure to an orthorhombic phase. Scheelites are antiferromagnetic with T_N ​≃ ​25 ​K. In the Tb scheelite the rare earth is strongly coupled to Cr⁵⁺ and the MCE exhibits the typical features of an antiferromagnet, i.e. a sort of Curie-Weiss behavior above T_N and a sudden drop to small or even inverse values below. In the Er and Ho scheelites the R³⁺-Cr⁵⁺ exchange coupling is very weak and the R³⁺ ion behaves independently of the Cr⁵⁺. As a striking consequence the MCE is quite stronger well below T_N.