Large reversible room-temperature magnetocaloric effect in the Ba0.5Sr1.5Zn2Fe12O22-related hexaferrites

The magnetic and magnetocaloric effect (MCE) of Mg or Cu-doped Ba0.5Sr1.5Zn2Fe12O22 hexaferrites synthesized by the sol-gel method are investigated. The Ba0.5Sr1.5Zn2Fe12O22 shows a sharp paramagnetic to ferrimagnetic phase transition and a large conventional MCE at around room temperature. By the partial substitution of Zn with Mg or Cu, the magnetic transition temperature as well as the maximum MCE temperature can be tuned in the range of 300 and 375 K while keeping the maximum MCE nearly unchanged, which are beneficial characteristics for their application as near room-temperature magnetic refrigerants. For Ba0.5Sr1.5Zn2Fe12O22, it is found that the maximum values of magnetic entropy change –ΔSM and relative cooling power (RCP) are 1.27 J/kg K and 124 J/kg for ΔH=4.4 T, respectively. Given its advantages, such as large RCP, suitable working temperature, low-cost raw materials, easy to synthesize, and environment-friendly, the Ba0.5Sr1.5Zn2Fe12O22 related hexaferrites may be potential candidates for room-temperature magnetic refrigeration.