Influence of the martensitic transformation kinetics on the magnetocaloric effect in Ni-Mn-In

Abstract

The inverse magnetocaloric effect (MCE) in Ni-Mn-based Heusler compounds occurs during the magnetostructural transition between low-temperature, low-magnetization martensite and hightemperature, high-magnetization austenite. In this study, we analyze the metamagnetic transformation of a Ni 49.8 Mn 35 In 15.2 compound by simultaneous adiabatic temperature change ΔT ad and strain Δl/l 0 measurements in pulsed magnetic fields up to 10 T. We observe a ΔT ad of -10 K and a Δl/l 0 of -0.22 % when the reverse martensitic transition is fully induced at a starting temperature of 285 K. By a variation of the magnetic field-sweep rates between 316 Ts -1 , 865 Ts -1 and 1850 Ts -1 , the transitional dynamics of the reverse martensitic transformation have been investigated. Our experiments reveal an apparent delay upon the end of the reverse martensitic transformation at field rates exceeding 865 Ts -1 which is related to the annihilation of retained martensite. As a consequence, the field hysteresis increases and higher fields are required to saturate the transition. In contrast, no time-dependent effects on the onset of the reverse martensitic transformation were observed in the studied field-sweep range. Our results demonstrate that kinetic effects in Heusler compounds strongly affect the magnetic cooling cycle, especially when utilising a multicaloric "exploiting-hysteresis cycle" where high magnetic fieldsweep rates are employed.

Influence of microstructure on the application of Ni-Mn-In Heusler compounds for multicaloric cooling using magnetic field and uniaxial stress

“…In addition, the combination of inverse and conventional magnetocaloric effect in the measured sample results in a ΔT ad falling below the predicted value. If ΔT ad and the required field change are compared to arc-molten Ni-Mn-In of a similar transition temperature a good agreement is found[45]. For the dependence of ΔT ad on T start and the applied magnetic field, similar trends as for Δs T (T,H) in Figure9can be noticed.…”

“…Table 1: Temperature-dependent evolution of lattice parameters (q represents the modulation vector), eigenvalues (λ 1 , λ 2 , λ 3 ), and total volume change ΔV/V 0 of the Ni-Mn-In powder upon cooling from 310 to 240 K. At 310 K, the powder is fully austenitic, while at 240 K it has almost completely transformed to martensite. The XRD patterns and the corresponding lattice parameters at 240 and 310 K were already shown in [45].…”

“…The latter enables higher fields and faster sweeping rates [21]. Simultaneously with ΔT ad the transformation strain ε tr was recorded which allows studying kinetical effects of the field-induced reverse martensitic transformation [45].…”

Microstructure engineering of metamagnetic Ni-Mn-based Heusler compounds by Fe-doping: A roadmap towards excellent cyclic stability combined with large elastocaloric and magnetocaloric effects

“…This is also confirmed by comparing ΔsT with the transition entropy changes Δst,A determined from DSC (see Table 3). Hence, even higher values of ΔsT and ΔTad can be achieved upon the reverse martensitic transformation when the magnetic field change is raised further [61]. The negative (positive) values of ΔsT (ΔTad) at high temperatures result from the conventional magnetocaloric effect being present around TC A .…”

Direct and Indirect Determination of the Magnetocaloric Effect in the Heusler Compound Ni1.7Pt0.3MnGa

“…On the other hand, one of the open problems for the application of magnetic materials for magnetic cooling is the quantitative knowledge of the role played by hysteresis and irreversibility effects. In [24][25][26][27][28], since the entropy change calculated from magnetization might be overestimated when compared with the entropy change calculated from specific heat measurements. This is due to the different characteristics of each technique and measurement history before each isothermal magnetization measurement.…”