Inverse and Conventional Dual Magnetocaloric Effects in Ni Substituted Y-Type Sr ₂Zn _2-XNi _xFe ₁₂O ₂₂ Hexaferrites

Abstract

The effects of Ni substitution on magnetic and magnetocaloric effect (MCE) are investigated in polycrystalline Y-type hexaferrites of Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0). With the increasing of temperature, the M-T curves indicate successive magnetic structure transitions exist in Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0), which play significant roles in MCE behaviors. As the Ni2+ doping ratio increases the shape of magnetic entropy change curves near room temperature evolves gradually from a table-like to a peak-like form. Particularly, a significant contrast betweenCMCE and IMCE is observed below 100 K, whose behavior can be inherently exploited for heat sink in magnetic refrigeration applications. Among this series samples, Sr2Zn1.2Ni0.8Fe12O22 displays the best CMCE and IMCE performances, with the maximum magnetic entropy change value of 0.78 J/kg K at 354 K and -0.56 J/kg K at 16 K for the magnetic field change 0 - 50 kOe, respectively. Our work demonstrates that Sr2Zn2-xNixFe12O22 hexaferrites have great potential to be tailored for magnetic refrigeration with special needs such as different operating temperature zones, Ericsson cycle or heat sink at refrigeration.

Keywords: Y-type hexaferrites, Magnetism, Magnetocaloric effect, Magnetic refrigeration