Anil Aryal

Magnetic, transport, and magnetocaloric properties of boron doped Ni-Mn-In alloys

The impact of B substitution in Ni50Mn35In15−xBx Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5–400 K). Direct adiabatic temperature change (ΔTAD) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni50Mn34.8In14.2B and Ni50Mn35In14X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔTAD = 2.5 K was observed at the magnetostructural transition for Ni50Mn35In14.5B0.5.

Phase transitions and magnetocaloric and transport properties in off-stoichiometric GdNi2Mnx

The structural, magnetic, magnetocaloric, transport, and magnetoresistance properties of the rare-earth intermetallic compounds GdNi2Mnx (0.5 ≤ x ≤ 1.5) have been studied. The compounds with x = 0.5 and 0.6 crystallize in the cubic MgCu2 type phase, whereas samples with x ≥ 0.8 form a mixed MgCu2 and rhombohedral PuNi3 phase. A second order magnetic phase transition from a ferromagnetic to paramagnetic state was observed near the Curie temperature (TC). The GdNi2Mnx (0.5 ≤ x ≤ 1.5) compounds order in a ferrimagnetic structure in the ground state. The largest observed values of magnetic entropy changes (at TC for ΔH = 5T) were 3.9, 3.5, and 3.1 J/kg K for x = 0.5, 0.6, and 0.8, respectively. The respective relative values of the cooling power were 395, 483, and 220 J/kg. These values are greater than some well-known prototype magnetocaloric materials such as Gd (400 J/kg) and Gd5Si2Ge2 (240 J/kg). Analysis of the resistivity data showed a T2 dependence at low temperatures, suggesting strong electron-phonon...

The effects of substituting Ag for In on the magnetoresistance and magnetocaloric properties of Ni-Mn-In Heusler alloys

The effect of substituting Ag for In on the structural, magnetocaloric, and thermomagnetic properties of Ni50Mn35In15−xAgx (x = 0.1, 0.2, 0.5, and 1) Heusler alloys was studied. The magnitude of the magnetization change at the martensitic transition temperature (TM) decreased with increasing Ag concentration. Smaller magnetic entropy changes (ΔSM) were observed for the alloys with larger Ag concentrations and the martensitic transition shifted to higher temperature. A shift of TM by about 25 K to higher temperature was observed for an applied hydrostatic pressure of P = 6.6 kbar with respect to ambient pressure. A large drop in resistivity was observed for large Ag concentration. The magnetoresistance was dramatically suppressed due to an increase in the disorder of the system with increasing Ag concentration. Possible mechanisms responsible for the observed behavior are discussed.

Giant field-induced adiabatic temperature changes in In-based off-stoichiometric Heusler alloys

Direct measurements of the adiabatic temperature change (ΔTAD) of Ni50Mn35In14.5B0.5 have been done using an adiabatic magnetocalorimeter in a temperature range of 250–350 K, and with magnetic field changes up to ΔH = 1.8 T. The initial susceptibility in the low magnetic field region drastically increases with temperature starting at about 300 K. Magnetocaloric effects parameters, adiabatic temperature changes, and magnetic entropy changes were found to be a linear function of H2/3 in the vicinity of the second order transitions (SOT), whereas the first order transitions do not obey the H2/3 law due to the discontinuity of the transition. The relative cooling power based on the adiabatic temperature change for a magnetic field change of 1.8 T has been estimated. Maximum values of ΔTAD = −2.6 K and 1.7 K were observed at the magnetostructural transition (MST) and SOT for ΔH = 1.8 T, respectively. The observed ΔTAD at the MST exceeds the ΔTAD for Ni50Mn35In14X with X = In, Al, and Ge by more than 20% and is...

Influence of copper substitution on the magnetic and magnetocaloric properties of NiMnInB alloys

The structural, magnetocaloric, and thermomagnetic properties of Ni 50.51Mn34.34−xCuxIn14.14B1.01 with x = (0, 1.26, and 2.02) have been studied using room-temperature x-ray diffraction, differential scanning calorimetry (DSC), and magnetization measurements. The partial substitution of Cu for Mn was found to shift both the martensitic transition temperature (TM) and the Curie temperature (TC) to lower temperatures. The values of the latent heat (L = 9.4 J/g) and corresponding magnetic (ΔSM) and total entropy (ΔST) changes (ΔSM = 22.60 J/kg K for ΔH = 5 T and ΔST = 29.7 J/kg K) have been evaluated using magnetic and DSC measurements, respectively, for the sample with x = 1.26. Large negative values of ΔSM of −7.27 and −5.98 J/kg K for ΔH = 5 T in the vicinity of TC were observed for x = 1.26 and 2.02, respectively. It has been found that the application of hydrostatic pressure changes the magnetic ground state of the martensitic phase and increases the temperature stability of the martensitic phase. The roles of the magnetic and structural changes on the transition temperatures are discussed.

Phase diagram and magnetocaloric effects in Ni1-xCrxMnGe1.05

The structural and magnetic properties of the Ni1−xCrxMnGe1.05 system (for x = 0, 0.035, 0.070, 0.105) have been studied by x-ray diffraction (XRD), differential scanning calorimetry (DSC), and magnetization measurements. A change in crystal structure from orthorhombic to hexagonal was observed in the XRD data at chromium concentrations of x = 0.035, 0.070, and 0.105. The values of the cell parameters and volume of the unit cell for orthorhombic and hexagonal phase were determined. It was found that the partial substitution of Cr for Ni in Ni1−xCrxMnGe1.05 results in a first order magnetostructural transition from antiferromagnetic to ferromagnetic (FM) at TM = 132 K for x = 0.105. A FM to paramagnetic second order transition has been observed at TC = 204 K. A magnetic entropy change of |ΔSM| = 4.5 J/kg K for ΔH = 5 T was observed in the vicinity of TC and TM for x = 0.105. The values of the latent heat (L = 2.2 J/g) and corresponding total entropy changes (ΔST = 16 J/kg K) have been determined from DSC m...

Phase Transitions and Magnetocaloric Properties in MnCo1−xZrxGe Compounds

The structural, magnetic, and magnetocaloric properties of () have been studied through X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Results indicate that the partial substitution of Zr for Co in decreases the martensitic transition temperature (). For = 0.02, was found to coincide with the ferromagnetic transition temperature () resulting in a first-order magnetostructural transition (MST). A further increase in zirconium concentration ( = 0.04) showed a single transition at . The MST from the paramagnetic to ferromagnetic state results in magnetic entropy changes () of 7.2 J/kgK for = 5 T at 274 K for = 0.02. The corresponding value of the relative cooling power (RCP) was found to be 266 J/kg for = 5 T. The observed large value of MCE and RCP makes this system a promising material for magnetic cooling applications.

Effects of the partial substitution of Ni by Cr on the transport, magnetic, and magnetocaloric properties of Ni50Mn37In13

The structural, magnetic, and magnetotransport properties of Ni50-xCrxMn37In13 Heusler alloys have been synthesized and investigated by x-ray diffraction (XRD), field and pressure dependent magnetization, and electrical resistivity measurements. The partial substitution of Ni by Cr in Ni50Mn37In13 significantly improves the magnetocaloric effect in the vicinity of the martensitic transition (TM). This system also shows a large negative entropy change at the Curie temperature (TC), making it a candidate material for application in a refrigeration cycle that exploits both positive and negative magnetic entropy changes. The refrigeration capacity (RC) values at TM and TC increase significantly by more than 20 % with Cr substitution. The application of hydrostatic pressure increases the temperature stability of the martensitic phase in Ni45Cr5Mn37In13. The influence of Cr substitution on the transport properties of Ni48Cr2Mn37In13 is discussed. An asymmetric magnetoresistance, i.e., a spin-valve-like behavior...

Microwave absorption through the martensitic and Curie transitions in Ni45Cr5Mn37In13

We have investigated the electron spin resonance (ESR) of the Ni45Cr5Mn37In13 Heusler alloy near the structural and magnetic phase transition temperatures. Ni45Cr5Mn37In13 is characterized by a first order magnetostructural (martensitic) transition (MST) with magneto-responsive properties such as magnetoresistance, Hall and magnetocaloric effects, etc., in the vicinity of the MST. Since the details and origins of these behaviors are not well understood, we used a technique beyond magnetometry, i.e., “microwave absorption”, to reveal new information. ESR studies of Ni45Cr5Mn37In13 shows that this compound is characterized by wide absorption spectra at temperatures greater than 250 K that depend on the angle of the magnetic field relative to the normal to the sample plate (α) and temperature (T). Two local maxima at about 5 and 6 kOe were detected for α close to zero degrees near the martensitic transition and Curie temperatures. The absorption spectra are discussed along with the results of the structural ...

Magnetostructural transitions and magnetocaloric effects in Ni50Mn35In14.25B0.75 ribbons

The structural, thermal, and magnetic behaviors, as well as the martensitic phase transformation and related magnetocaloric response of Ni50Mn35In14.25B0.75 annealed ribbons have been investigated using room-temperature X-ray diffraction (XRD), differential scanning calorimetry (DSC), and magnetization measurements. Ni50Mn35In14.25B0.75 annealed ribbons show a sharper change in magnetization at the martensitic transition, resulting in larger magnetic entropy changes in comparison to bulk Ni50Mn35In14.25B0.75. A drastic shift in the martensitic transformation temperature (TM) of 70 K to higher temperature was observed for the annealed ribbons relative to that of the bulk (TM = 240 K). The results obtained for magnetic, thermal, structural, and magnetocaloric properties of annealed ribbons have been compared to those of the corresponding bulk alloys.