(07A910) Magnetocaloric materials with first-order phase transition: thermal and magnetic hysteresis in LaFe_(11.8)Si_(1.2) and Ni(2.21)Mn_(0.77)Ga_(1.02) (invited)

摘要

This is a report on a comparative study of thermal and magnetic hysteresis in LaFe_(11.8)Si_(1.2) and Ni(2.21)Mn_(0.77)Ga_(1.02) polycrystalline samples near their first-order phase transitions by measurements of magnetization and direct measurements of the adiabatic temperature change, ΔT_(ad)(H). Based on the obtained M(T) and M{H) dependencies, H-T diagrams were constructed for both alloys and used to explain the ΔT_(ad)(H) dependencies. For low thermal hysteresis and a sharp transition in the temperature dependence of magnetization (LaFe_(11.8)Si_(1.2)), the field dependencies of ΔT_(ad)(H) are governed by the phase boundary between ferromagnetic and paramagnetic states. For large thermal hysteresis and a broad transition width in temperature (Ni(2.21)Mn_(0.77)Ga_(1.02)), the phase boundary has little impact on ΔT_(ad)(H). It is also shown that, in the phase transition region, ΔT_(ad) measured upon the first application of magnetic field (virgin ΔT_(ad)(H) leg) can differ from that measured upon subsequent runs of the field. This can lead to an overestimation of the magnetocaloric effect, if only the virgin leg of ΔT_(ad){H) is considered.