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 larger than the Gd based Heusler alloys

Multifunctional properties related to magnetostructural transitions in ternary and quaternary Heusler alloys

In this report, the results of a study on the effects of compositional variations induced by the small changes in concentrations of the parent components and/or by the substitution of Ni, Mn, or In by an extra element Z, on the phase transitions, and phenomena related to the magnetostructural transitions in off-stoichiometric Ni-Mn-In based Heusler alloys are summarized. The crystal structures, phase transitions temperatures, and magnetic and magnetocaloric properties were analyzed for representative samples of the following systems (all near 15 at% indium concentration): Ni-Mn-In, Ni-Mn-In-Si, Ni-Mn-In-B, Ni-Mn-In-Cu, Ni-Mn-In-Cu-B, Ni-Mn-In-Fe, Ni-Mn-In-Ag, and Ni-Mn-In-Al

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, has been observed near TM for Ni48Cr2Mn37In13

The Comparison of Direct and Indirect Methods for Determining the Magnetocaloric Parameters in the Heusler Alloy Ni50Mn34.8In14.2B

The magnetocaloric properties of the Ni50Mn34.8In14.2B Heusler alloy have been studied by direct measurements of the adiabatic temperature change (ΔTAD(T,H)) and indirectly by magnetization (M(T,H)), differential scanning calorimetry, and specific heat (C(T,H)) measurements. The presence of a first-order ferromagnetic-paramagnetic transition has been detected for Ni50Mn34.8In14.2B at 320 K. The magnetocaloric parameters, i.e., the magnetic entropy change (ΔSM = (2.9-3.2) J/kgK) and the adiabatic temperature change (ΔTAD = (1.3-1.52) K), have been evaluated for ΔH = 1.8 T from CP(T,H) and M(T,H) data and from direct ΔTAD(T,H) measurements. The extracted magnetocaloric parameters are comparable to those of Gd

NMR studies of the ground states of Ni50-xCoxMn35In15 (x=1, 2.5) and Ni45Co5Mn37In13 Heusler alloys

Three temperature-induced phase transitions at T=T1, TM/TA, and TC, related to the ferromagnetic order of the martensitic phase (FMMP), martensitic (structural) transitions (MT), and the ferromagnetic order of the austenitic phase (FMAP), respectively, have been observed in the off-stoichiometric Heusler alloys, Ni50-xCoxMn35In15 (x=1, 2.5) and Ni45Co5Mn37In13. The phase transitions temperatures are found to be depended on alloy composition. A kinetic arrest of the AP was observed for Ni47.5Co2.5Mn35In15 in the magnetization measurements during field-cooling cycle (FCC) at 50 kOe. Depending upon the cooling protocols, ZFC and FCC (at H = 50 kOe), two different ground states of the alloys can be found in Ni47.5Co2.5Mn35In15 and Ni45Co5Mn37In13 alloys. The ground states (T=4.2 K and external field H=0) of the alloys was found to be characterized by three main line: two, partially overlapping, at higher frequencies (300-450 MHz), most likely corresponding of manganese resonance lines and one at lower frequency at about 200 MHz. A significant shift in the spectrum of Ni45Co5Mn37In13 by about 100 MHz to higher frequencies was observed. The correlation of magnetizations obtained from magnetic moment and NMR studies is discussed

High field magnetoresistance of nanocomposites (Co84Nb14Ta2)X(Al2O3)100-X near the percolation threshold

We present results of experimental studies of magnetic properties, resistivity and magnetoresistance (MR) of (Co84Nb14Ta2)x(Al2O3)100-x films deposited onto a glass-ceramic substrate by the ion-beam sputtering, focusing on MR in high magnetic fields for compositions close to the percolation threshold (x=47-57 at.%). The samples consist on Co-Nb-Ta metallic nanogranules size of 2-5 nm which are embedded into the non-stoichiometric Al-O matrix. Magnetization was measured by SQUID magnetometer at T=4.2-350 K. MR was studied in the pulsed magnetic fields μ0H up to 20 T at T=70-300 K in three geometries: magnetic field in plane parallel and perpendicular to current, magnetic field perpendicular to plane. The pulse duration was 11-12 ms. For the sample with x=57 at.% the temperature dependence of conductivity follows the lnT behavior that matches a strong tunnel coupling between nanogranules. With decreasing metal volume fraction lnT behavior gradually changes to the T1/2 dependence at 47 at.%. For all samples MR is small (<1%) and negative. For x<57 at.% it is slightly anisotropic at μ0H<1.0 T and almost saturates with increasing magnetic field. There is an evidence of small positive contribution to MR at μ0H=20T. Accordingly to structural and magnetic data a large amount of metallic atoms are located between magnetic nanogranules that diminish the tunnel barrier height and make tunnel MR small and weakly dependent on temperature

High field magnetoresistance of nanocomposites (Co

We present results of experimental studies of magnetic properties, resistivity and magnetoresistance (MR) of (Co84Nb14Ta2)x(Al2O3)100-x films deposited onto a glass-ceramic substrate by the ion-beam sputtering, focusing on MR in high magnetic fields for compositions close to the percolation threshold (x=47-57 at.%). The samples consist on Co-Nb-Ta metallic nanogranules size of 2-5 nm which are embedded into the non-stoichiometric Al-O matrix. Magnetization was measured by SQUID magnetometer at T=4.2-350 K. MR was studied in the pulsed magnetic fields μ0H up to 20 T at T=70-300 K in three geometries: magnetic field in plane parallel and perpendicular to current, magnetic field perpendicular to plane. The pulse duration was 11-12 ms. For the sample with x=57 at.% the temperature dependence of conductivity follows the lnT behavior that matches a strong tunnel coupling between nanogranules. With decreasing metal volume fraction lnT behavior gradually changes to the T1/2 dependence at 47 at.%. For all samples MR is small (<1%) and negative. For x<57 at.% it is slightly anisotropic at μ0H<1.0 T and almost saturates with increasing magnetic field. There is an evidence of small positive contribution to MR at μ0H=20T. Accordingly to structural and magnetic data a large amount of metallic atoms are located between magnetic nanogranules that diminish the tunnel barrier height and make tunnel MR small and weakly dependent on temperature

Asymmetric magnetoresistance in bulk In-based off-stoichiometric Heusler alloys

It has been found that Ni50Mn35In14B exhibits with increasing temperature a first-order magnetostructural phase transition from a low-magnetization martensitic phase to a high-temperature ferromagnetic austenitic phase at TM~315 K as observed from magnetization M(T) curves with H=0.05 T. A shift in TM of about 12 K towards lower temperatures has been detected under application of a 5T magnetic field. An asymmetric magnetoresistance (spin-valve-like behavior) has been observed in the vicinity of TM at 304 K after the initial application of magnetic field that could be related to the kinetic arrest and de-arrest of a fractional austenite phase in the vicinity of phase co-existence. A possible origin of a spin-valve-like MR in Ni50Mn35In14B, and its relation to structural, magnetic, and magnetocaloric properties, has been discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Magnetocaloric effect and multifunctional properties of Ni-Mn-based Heusler alloys

The studies of magnetocaloric properties, phase transitions, and phenomena related to magnetic heterogeneity in the vicinity of the martensitic transition (MT) in Ni-Mn-In and Ni-Mn-Ga off-stoichiometric Heusler alloys are summarized. The crystal structure, magnetocaloric effect (MCE), and magnetotransport properties were studied for the following alloys: Ni 50Mn 50-xIn x, Ni 50-xCo xMn 35In 15, Ni 50Mn 35-xCo xIn 15, Ni 50Mn 35In 14Z (Z=Al, Ge), Ni 50Mn 35In 15-xSi x, Ni 50-xCo xMn 25yGa 25-y, and Ni 50-xCo xMn 32-yFeyGa 18. It was found that the magnetic entropy change, ΔS, associated with the inverse MCE in the vicinity of the temperature of the magneto-structural transition, TM, persists in a range of (125-5) J/(kg K) for a magnetic field change ΔH=5 T. The corresponding temperature varies with composition from 143 to 400 K. The MT in Ni 50Mn 50-xIn x (x=13.5) results in a transition between two paramagnetic states. Associated with the paramagnetic austenite-paramagnetic martensite transition ΔS=24 J/(kg K) was detected for ΔH=5 T at T=350 K. The variation in composition of Ni 2MnGa can drastically change the magnetic state of the martensitic phase below and in the vicinity of TM. The presence of the martensitic phase with magnetic moment much smaller than that in the austenitic phase above TM leads to the large inverse MCE in the Ni 42Co 8Mn 32-yFeyGa 18 system. The adiabatic change of temperature (ΔT ad) in the vicinity of TC and TM of Ni 50Mn 35In 15 and Ni 50Mn 35In 14Z (Z=Al, Ge) was found to be ΔT ad=-2 K and 2 K for ΔH=1.8 T, respectively. It was observed that |ΔT ad|≈1 K for ΔH=1 T for both types of transitions. The results on resistivity, magnetoresistance, Hall resistivity in some In-based alloys are discussed. © 2012 Elsevier B.V