A unified approach to describe the thermal and magnetic hysteresis in Heusler alloys

Abstract

Different excitations, like temperature, magnetic field, or pressure, can drive a martensitic transition in Heusler alloys. Coupled phenomena in these materials lead to interesting magnetocaloric and barocaloric effects ascribed to this transition. In this work, we demonstrate that isothermal transformations induced by a magnetic field and isofield transformations induced by the temperature can be described using the same framework. By defining an effective temperature that relates field and temperature through the properties of the system (magnetic moment and entropy of the transition), both kinds of loops can be transformed into the other kind, therefore providing a more effective way of characterizing hysteretic samples. The validity of this effective temperature approach to describe the transition holds for martensite to austenite transformations as well as reversal ones, and thus, the hysteresis phenomena can be described using this single general excitatio

A Comparative Study on the Magnetocaloric Properties of Ni‐Mn‐X(‐Co) Heusler Alloys

“…The martensite formation branch upon cooling is shifting stronger than the austenite formation branch upon heating as the temperature of both branches differ by the initially present thermal hysteresis. The increasing hysteresis with decreasing temperature is in accordance with this phenomenon by assuming that it is not relevant whether the transition temperature is shifted by a magnetic field or compositional changes . However, this trend for Δ T Hys is absent for the evolution of the hysteresis in Ni‐Mn‐Sn, where also Δ M as well as do not show large changes as a function of A s .…”

Ultra-low hysteresis in giant magnetocaloric Mn1-V Fe0.95(P,Si,B) compounds

“…The iso-thermal entropy change |ΔS M | is widely used as a criterion to evaluate the amount of heat transferred in one thermodynamic cycle. The values of |ΔS M | are derived from iso-field magnetization curves using the Maxwell relation [36,37]. The isofield magnetization curves of series A and B for a magnetic field change are measured in the vicinity of T C with a temperature interval of 1 K. In order to minimize the effect of demagnetization factor, the applied magnetic field starts from 0.6 T and increases to 2 T in a step of 0.1 T. The calculated temperature dependence of |ΔS M | for series A and B are shown in Fig.…”

Thermo-magnetic characterization of phase transitions in a Ni-Mn-In metamagnetic shape memory alloy

“…This protocol assures a fully martensite state for each magnetization curve obtained below (but close to) the austenite start temperature at zero field. In fact, after magnetization has induced formation of austenite, hysteretic behavior ascribed to the transition makes that removing the field cannot yield a zero austenite fraction [8]. Complementary magnetization curves were obtained from the sample after measuring at 352 K and cooling from 250 K to 170 K to register the Curie transition of the martensite phase.…”