Abstract
The structural, magnetic, magnetocaloric, and transport properties of Ni50Mn35In15-xBix (x = 0, 0.25, 0.5, 1, 1.5) compounds has been studied through X-ray diffraction (XRD), differential scanning calorimetry, and magnetization measurements. A mixture of high temperature austenite phase (AP) and low temperature martensitic phase (MP) was observed from the XRD at room temperature. The saturation magnetization MS at 10 K was found to decrease with increasing Bi content. A shift in the martensitic transition temperature (TM) relative to the parent compound was observed with a maximum shift of ∼ 36 K for x = 1.5. Abnormal shifts in TC and TM to higher temperatures were observed at high field for x ≥ 0.5. Large magnetic entropy changes (ΔSM) of about 40 J/kg K (x = 0) and 34 J/kg K (x = 0.25) were observed at TM with H = 5 T, which reduced significantly for higher Bi concentrations. The doping of small amounts of Bi in the In sites increased the peak width of the ΔSM curves at the second order transition, leading to larger values of relative cooling power. A significant magnetoresistance (-30%) was observed near TM with ΔH = 5T for x = 0.5.
Highlights
The magnetocaloric effect (MCE) is an adiabatic temperature change (∆TA) or isothermal magnetic entropy change (∆SM) in a magnetic material, induced by an applied magnetic field
The room temperature X-ray diffraction (XRD) patterns for Ni50Mn35In15-xBix are shown in Fig.[1] (a)
A relative shift in the XRD peaks towards lower two theta angles with respect to the parent compound was observed for the austenitic phase (AP), which indicates an increase in the lattice parameters since the metallic radius of Bi (1.70 Å) is greater than that of In (1.663 Å).[15]
Summary
The magnetocaloric effect (MCE) is an adiabatic temperature change (∆TA) or isothermal magnetic entropy change (∆SM) in a magnetic material, induced by an applied magnetic field. A coincidence of magnetic and structural phase transitions (known as a MST) from a low magnetic state of the MP to a ferromagnetic state of the AP at TM has been observed in these compounds.[7,8,11] Such MSTs result in a large jump in magnetization that is necessary for large MCEs. As reported in Ref. 11, changing the stoichiometry or chemical composition, or doping an extra element in the Ni-Mn-In based Heusler alloys changes the conduction electron concentration (e/a), interatomic MnMn distance, and the Ni(3d)-Mn(3d) hybridization. As reported in Ref. 11, changing the stoichiometry or chemical composition, or doping an extra element in the Ni-Mn-In based Heusler alloys changes the conduction electron concentration (e/a), interatomic MnMn distance, and the Ni(3d)-Mn(3d) hybridization These factors can modify the electronic band structure and affect the phase transitions and the associated phenomena.[12] the exact mechanisms responsible for the unique behaviors of off-stoichiometric Ni-Mn-In based Heusler alloys are not clear.
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