Heat capacity and magnetocaloric effect in the zircon and scheelite phases of RCrO4, R = Tb, Er, Ho

• Published in: Journal of solid state chemistry Vol. 314; p. 123356
• Main Authors: Palacios, E., Castro, M., Romero de Paz, J., Gallardo-Amores, J.M., Sáez-Puche, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-10-2022
• Subjects: Heat capacity and entropy; Magnetic measurements; Magnetocaloric effect; Polymorphism of RCrO4 oxides; Magnetic measurements; Magnetocaloric effect; Polymorphism of RCrO4 oxides; Heat capacity and entropy
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2022.123356

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.
Zircon RCrO4 phases show large magnetocaloric effect according to their ferromagnetic behavior. This effect as it is expected is lower in the case of antiferromagnetic scheelite polymorphs. [Display omitted]
•Zircon to scheelite RCrO4 (R ​= ​Tb, Ho, Er) phase transition induced at high pressure and high temperature.•Magnetic measurements reveal that RCrO4 Zircons behave as ferromagnetic while the RCrO4 Scheelites are antiferromagnetic.•Magnetic and calorimetric measurements to determine the magnetic entropy variation for the zircon and scheelite RCrO4 oxides.•Zircon RCrO4 phases show large magnetocaloric effect. This effect appear to be lower in the case of scheelite polymorphs.