Magnetic Properties of LaCr1−xMxSb3 (M=V, Mn, Fe, Cu, and Al)

The influence of Cr substitution by various metals (M=V, Mn, Fe, Cu and Al) on the magnetic state of the itinerant intermetallics La(Cr,M)Sb3 was studied by magnetization and magnetic susceptibility measurements up to 55 kG at 5 K and from 4.2 to 400 K, in a magnetic field of 1000 G, respectively. It was found that the Curie temperature (TC) and magnetization (M) of these compounds depend nonlinearly on the concentration, remaining in the vicinity of the values of TC and M measured for LaCrSb3. Curie temperatures and magnetization values at 55 kG are suppressed by Mn, Fe, V, and Cu, and have a slight maximum at low Al concentration (about 5%)

Magnetic Behavior of Iron-Oxoclusters Prepared in an Organosilica Sol–Gel Matrix

The crystal structure and magnetization of nanoscale enTMOS–Fe2O3 sol–gel composites with weight iron concentration x, varying from 0.003 to 0.065, have been studied by the transmission electron microscopy technique and a superconducting quantum interference device magnetometer. The clusters are crystallized in a hexagonal crystal structure. All the samples demonstrate a superparamagnetic behavior with antiferomagnetic cluster–cluster coupling at low temperature. The effective paramagnetic moment, μeff, has been found to vary in the range from 5.9 (S=5/2) to 2.5 μB per iron ion. The concentration dependence of the μeff shows a minimum for x∼0.01. At a low iron concentration x\u3c0.01, μeff is practically independent of x and equals about 6 μB per Fe ion. The concentration interval 0.01\u3cx\u3c0.07 is characterized by a monotonical increase of μeff from 2.5 to about 3 μB per Fe ion. Thus, an abrupt variation of μeff (about two times) is observed at x≈0.01. It has been shown that such behavior can be caused by competition between the uncoupled “surface” and antiferromagnetically coupled “bulk” Fe magnetic moments

Evidence of Martensitic Phase Transitions in Magnetic Ni-Mn-In Thin Films

Ni 50Mn35In15 Heusler alloy thin films (with thicknesses of about 10 nm) have been grown on single crystal MgO and SrTiO3 (STO) (100) substrates using a laser-assisted molecular beam epitaxy method. Films of mixed austenitic and martensitic phases and of pure martensitic phase have been detected for those grown on MgO and STO substrates, respectively. Thermomagnetic curves were measured using a SQUID magnetometer and are consistent with those of off-stoichiometric In-based bulk Heusler alloys, including a martensitic transition at T = 315 K for films grown on MgO. The differences in the properties of the films grown on MgO and STO are discussed

Magnetocaloric Properties of the Ni2Mn1−x(Cu,Co)xGa Heusler Alloys

We have investigated the magnetocaloric properties on the Ni2Mn1−xAxGa Heusler alloys with partial substitution of Mn by A = Co (x = 0.10, 0.20, and 0.30) and Cu (x = 0.15 and 0.20) in the vicinity of the martensitic transition by measuring magnetization curves at magnetic field up to 20 kOe and in the temperature range of 250–300 K. The changes of the magnetic part of entropy dependence on magnetic field and temperature have been evaluated

Compressive Response of Polycrystalline NiCoMnGa High-Temperature Meta-magnetic Shape Memory Alloys

The effects of the addition of quaternary element, Co, to polycrystalline NiMnGa alloys on their magnetic and shape memory properties have been investigated. NiCoMnGa polycrystalline alloys have been found to demonstrate good shape memory and superelasticity behavior under compression at temperatures greater than 100 °C with about 3% transformation strain and low-temperature hysteresis. It is also possible to train the material to demonstrate a large two-way shape memory effect

Probing the electronic structure of Ni–Mn–In–Si based Heusler alloys thin films using magneto-optical spectra in martensitic and austenitic phases

Thin films of Ni52Mn35−xIn11+xSi2 were fabricated by magnetron sputtering on MgO (0 0 1) single crystal substrates. Magnetization as function of temperature for Ni52Mn35In11Si2 exhibits features consistent with a magnetostructural transition (MST) from an austenitic phase to a martensitic phase, similar to the bulk material. We observed that the martensitic transformation is externally sensitive to small changes in chemical composition and stoichiometry. It has been found that thin films of Ni52Mn34−xIn11+xSi2 with x = 0 and 1 undergo a temperature-induced MST or remain in a stable austenitic phase, respectively. Comparison of magneto-optical transverse Kerr effect spectra obtained at 0.5–4.0 eV in the 35–300 K temperature interval reveal insignificant differences between the martensitic and austenite phases. We found that the field and temperature dependencies of the transverse Kerr effect are quite different from the magnetization behavior, which is attributed to magnetic inhomogeneity across the films. To elucidate the effects of magnetostructural phase transitions on the electronic properties, we performed density functional calculations of the magneto-optical Kerr effect

Magnetocaloric and Magnetic Properties of Ni\u3csub\u3e2\u3c/sub\u3eMn\u3csub\u3e1-x\u3c/sub\u3eCu\u3csub\u3ex\u3c/sub\u3eGa Heusler Alloys: an Insight from the Direct Measurements and \u3ci\u3eab initio\u3c/i\u3e and Monte Carlo Calculations

We calculated magnetic exchange constants and magnetocaloric properties of Ni2Mn1-xCuxGa Heusler alloys by ab initio and Monte Carlo methods. The ab initio study of the influence of the Cu excess x on the strength of magnetic interactions revealed that Cu weakens Mn-Ni interaction and has a complex impact on the Mn-Mn interactions. Theoretically calculated magnetic phase diagram of Ni2Mn1-xCuxGa is in a good agreement with available experimental data. Calculated by the Monte Carlo method the isothermal magnetic entropy change Delta Smag in a Ni2Mn0.75Cu0.25Ga alloy is significantly smaller around the coupled magnetostructural phase transition temperature than the reported earlier experimental Delta Smag. This discrepancy is ascribed to an overestimation of the experimental Delta Smag at the magnetostructural phase transition. Theoretically determined adiabatic temperature change Delta Tad in Ni2Mn0.75Cu0.25Ga agrees well with Delta Tad measured experimentally by a direct method

Direct Measurements of Field-Induced Adiabatic Temperature Changes Near Compound Phase Transitions in Ni–Mn–In Based Heusler Alloys

The adiabatic temperature changes (ΔTad) in the vicinity of the Curie and martensitic transition temperatures of Ni50Mn35In15 and Ni50Mn35In14Z (Z = Al and Ge) Heusler alloys have been studied using an adiabatic magnetocalorimeter of 250–350 K temperature interval for applied magnetic field changes up to ΔH = 1.8 T. The largest measured changes were ΔTad = −2 and 2 K near the martensitic (first-order) and ferromagnetic (second-order) transitions for ΔH = 1.8 T, respectively. It was observed that |ΔTad| ≈ 1 K for relatively small field changes (ΔH = 1 T) for both types of transitions. The results indicate that these materials should be further explored as potential working materials in magnetic refrigeration applications