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, TC ≃ 20 K, reaching maximum isothermal entropy increments, |ΔST| = 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 TD = 60 K associated to a Jahn-Teller transition from the tetragonal zircon structure to an orthorhombic phase. Scheelites are antiferromagnetic with TN ≃ 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 TN 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 TN.