Exchange Bias Behavior in Ni–Mn–Sb Heusler Alloys

The authors report the observation of exchange bias in bulk polycrystalline Ni50Mn25+xSb25−x Heusler alloys. Shifts in hysteresis loops of up to 248 Oe were observed in the 5 T field cooled samples. The observed exchange bias behavior in Ni50Mn25+xSb25−x is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. Such behavior is an addition to the multifunctional properties of the Ni50Mn25+xSb25−x Heusler alloy system

The Structural and Magnetic Properties of Ni2Mn1−xMxGa (M = Co, Cu)

In Ni2MnGa (cubic structure of L21 type) a first order martensitic structural transition, from the parent cubic (austenitic) phase to a low temperature complex tetragonal structure, takes place at TM = 202 K, and ferromagnetic order in the austenitic phase sets at TC = 376 K. In this work, the Mn sites in Ni2MnGa have been partially substituted with magnetic Co and nonmagnetic Cu, and the influence of these substitutions on the structural and magnetic properties of Ni2Mn1−xMxGa (M = Co and Cu) have been studied by XRD and magnetization measurements. X-ray diffraction patterns indicate that the Co doped system possess a highly ordered Heusler alloy L21 type structure for 0.05\u3cx\u3c0.12, and the Cu doped compounds possess L21 structure for 0.05\u3cx\u3c0.10. The ferromagnetic ordering temperature increases with increasing Co concentration for this system, and rapidly decreases with increasing Cu concentration. Both systems show the increase in TM with increasing Co and Cu concentration. (T-x) phase diagrams have been plotted. The results are discussed in terms of 3d-electron concentration variation

Magnetic and Electrical Properties of Ni50Mn35In15−xSix Heusler Alloys

We have studied the magnetic and electrical properties of the polycrystalline ferromagnetic Ni50Mn35In15−xSix (1 ≤ x ≤ 5) Heusler alloys through magnetization, thermal expansion, and resistivity measurements. It was observed that an increase in Si concentration strongly affects the ground state of the martensitic phase and the magnetic properties of compounds. A magnetic phase diagram has been constructed for these alloys. It was found that both martensitic transition temperature (TM) and Curie temperature of austenitic phase (TC) decrease, while ferromagnetic ordering temperature of the martensitic phase increases with increasing Si concentration. The magnetoresistance (Δρ/ρ) associated with martensitic transformation was found to vary from –47% for x = 2 at T = 261 K to −26% for x = 5 at T = 230 K for a magnetic field change of 5 T

Exchange Bias in Bulk Mn Rich Ni–Mn–Sn Heusler Alloys

An experimental study on the exchange bias properties of bulk polycrystalline Ni50Mn50−xSnx Heusler alloys has been performed. Martensitic transformations have been observed in the alloys for some critical Sn concentrations. The alloys, while in their respective martensitic phases, are found to exhibit exchange bias effect. Shifts in hysteresis loops of up to 225 Oe were observed in the 50 kOe field cooled samples. The observed exchange bias behavior in Ni50Mn50−xSnx is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system

Phase Transitions and Corresponding Magnetic Entropy Changes in Ni2Mn0.75Cu0.25−xCoxGa Heusler Alloys

Detailed studies of room temperature crystal structures, phase transitions, and related magnetic entropy changes (ΔSm) in shape memory alloys Ni2Mn0.75Cu0.25−xCoxGa (x = 0.0, 0.01, 0.02,0.025 0.03, 0.05) have been carried out by x-ray diffraction, magnetization, and thermal expansion measurements in magnetic fields of up to 5 T and in a temperature interval of 5–400 K. The high temperature austenitic cubic phase passes through a magnetic transition to ferromagnetic state and a structural transition to martensitic phase at the same temperature for all samples of the Ni2Mn0.75Cu0.25−xCoxGa system. The first order magnetostructural transition temperature increases from 308 to 345 K with increasing Co concentration. All of the alloys in the Ni2Mn0.75Cu0.25−xCoxGa system were found to possess large magnetic entropy changes. The maxima in the magnetic entropy changes ranged from ΔSmmax = −48 J/kg K to −64 J/kg K in a temperature range of 308–345 K

Large Magnetic Entropy Change in Ni50Mn50−xInx Heusler Alloys

The magnetocaloric properties of polycrystalline Ni50Mn50−xInx (15 ⩽ x ⩽ 16) associated with the second order magnetic transition at the Curie temperature and the first order martensitic transition were studied using magnetization measurements. The refrigeration capacity and magnetic entropy change were found to depend on the In concentration and reach a maximum value of refrigeration capacity of 280 J/kg with a magnetic entropy change of −6.8 J/kg K at 318 K for a magnetic field change of 5 T. These values of the magnetocaloric parameters are comparable to that of the largest values reported near the second order transition of metallic magnets near room temperature

Size Induced Variations in Structural and Magnetic Properties of Double Exchange La0.8Sr0.2MnO3−δ Nano-Ferromagnet

A detailed study on the influence of particle size varied from 8 nm to 53 nm on the structural and magnetic properties of La0.8Sr0.2MnO3−δ has been done. The unit cell volume increases and the microstrain in the compound shows peak formation as the particle size decreases. Nano particles of La0.8Sr0.2MnO3−δ exhibit superparamagnetism whose blocking temperature has a nonlinear and logarithmic decreasing tendency as function of particle size and applied magnetic field, respectively. Evidence of formation of a magnetically dead layer at the surface has been found and the ratio of the thickness of the dead layer to the particle size increases exponentially with particle size. The coercivity of the nanoparicles increases manifold as particle size varies from 53 nm to 21 nm. In the single domain region the coercivity exhibits a d−1.125 behavior. The temperature dependence of the saturation magnetization shows strong collective excitation due to the spin wave that varies as Tα with α\u3eαbulk of 3/2. Thus the spin wave does not follow the Bloch law in the case of nano particles of La0.8Sr0.2MnO3−δ

Magnetic and Magnetocaloric Properties of the New Rare-Earth-Transition-Metal Intermetallic Compound Gd3Co29Ge4B10

The compounds Gd3-xYxCo29Ge4B10 (x = 0, 0.5, 1.0, 1.5, and 3.0), Gd3Co29Al4B10, and Gd3Co29Al4B10 were synthesized by arc melting, and their magnetic properties investigated as a function of temperature and applied magnetic field. X-ray measurements showed primarily single-phase samples with the tetragonal crystal structure P4/nmm. It was found that Gd3Co29Ge4B10 orders ferromagnetically at TC  = 212 K and shows a compensation point at 128 K, indicating a ferrimagnetic ordering of the Co and Gd moments. An entropy change of −ΔS = 0.5 J/kgK was observed in a 5-T field at TC for this sample, while a change in sign for this quantity was observed both at the maximum value of magnetization (around 200 K) and then again at the compensation point. Substitution of Y for Gd in Gd3Co29Ge4B10 does not affect the Curie temperature, but shifts the compensation point to lower temperatures. This indicates that a decrease in Gd concentration does not affect the d-d exchange interaction, but has a pronounced effect on the f-d exchange interaction

Magnetic, Magnetocaloric, and Magnetoelastic Properties of LaFe(11.57)Si(1.43)B(x) Compounds

We have studied the magnetic, magnetocaloric, and magnetoelastic properties of LaFe11.57Si1.43Bx compounds in the concentration interval 0\u3cx ≤ 1.64 using magnetization and strain gauge techniques. The crystal cell parameters and Curie temperatures were found to increase linearly with increasing B concentrations up to ∼ 0.1% and 9%, respectively. A positive magnetovolume anomaly of about 0.22% was observed in the vicinity of TC. The magnetovolume coupling constant was estimated to be approximately 3×10−3 [μB/Fe atom]−2. Magnetic entropy changes at TC slightly depended on B concentration. A hysteresis loss of about ten times smaller relative to the base compound (x = 0) was observed for x = 1.64. Therefore it was shown that the characteristics of the magnetocaloric effect of LaFe11.57Si1.43 can be adjusted by a change in B concentration in the LaFe11.57Si1.43Bx system. The relative importance of the variation in the volume of crystal cell and electron concentration on TC was discussed

Giant reversible barocaloric response of (MnNiSi)(1-x)(FeCoGe)(x) (x=0.39, 0.40, 0.41)

MnNiSi-based alloys and isostructural systems have traditionally demonstrated impressive magnetocaloric properties near room temperature associated with a highly tunable first-order magnetostructural transition that involves large latent heat. However, these materials are limited by a small field-sensitivity of the transition, preventing significant reversible effects usable for cooling applications. Instead, the concomitant large transition volume changes prompt a high pressure-sensitivity, and therefore, promise substantial barocaloric performances, but they have been sparsely studied in these materials. Here, we study the barocaloric response in a series of composition-related (MnNiSi)1-x(FeCoGe)x (x = 0.39, 0.40, 0.41) alloys that span continuously over a wide temperature range around ambient. We report on giant reversible effects of ~40 J K-1 kg-1 and up to ~4 K upon application of ~2 kbar and find a degradation of the first-order transition properties with pressure that limits the barocaloric effects at high pressures. Our results confirm the potential of this type of alloys for barocaloric applications, where multicaloric and composite possibilities, along with the high density and relatively high thermal conductivity, constructively add to the magnitude of the caloric effects.Peer ReviewedPostprint (published version