Structural, magnetic, and magnetocaloric properties of Fe_7Se_8 single crystals

摘要

The magnetocaloric effect has been studied in high quality single crystals of Fe7Se8 (3c type) grown by using Bridgman's method. Magnetization and magnetocaloric effect measurements have been carried out in a magnetic field up to 5 T over the temperature range from 2 to 490 K. The spin reorientation transition from the easy c-axis to the easy c-plane, proceeding in an abrupt fashion, as a first-order phase transition, has been observed near the temperature T-R approximate to 125 K. The magnetization curves in the vicinity of this transition were shown to have an S-shape with a clear hysteresis. The first order metamagnetic field induced transitions have been identified above and below T-R. The conventional magnetocaloric effect related to the metamagnetic transitions has been found above T-R, while below T-R the inverse magnetocaloric effect was clearly seen. The existence of both kinds of magnetocaloric effect is important from the point of view of large rotating field entropy change in Fe7Se8 single crystals. The refrigeration capacity associated with a second order phase transition from the ferrimagnetic to the paramagnetic state at the Neel temperature T-N approximate to 450 K was found to be weaker than that appearing near T-R. The giant anisotropy of the magnetocaloric effect was related to the magnetic anisotropy of Fe7Se8 crystals. The one-ion model of the magnetocaloric effect has been developed and its predictions have been compared with experimental data. Published by AIP Publishing.