Phase stability and magnetic properties of the Heusler alloy Mn2 CuAl ribbons (original) (raw)
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Magnetic, microstructural and magnetoresistive properties of Heusler melt spun ribbons
NATIONAL CONFERENCE ON PHYSICS AND CHEMISTRY OF MATERIALS: NCPCM2020
In the present report, we have investigated the magnetic, microstructural, and magnetoresistive properties of Mn rich Mn-Ni-Sn full Heusler alloy ribbons, prepared by melt spinning technique. They show the first order structural (i.e. martensitic) transition above room temperature from the austenite phase to the martensite phase. This observation is also supported by the XRD and microstructural analysis, where the elongated thin strips have been found inside the grains, which correspond to the martensitic phase twin variants. They show a maximum negative MR of around 4 % near the martensitic transition. In the present ribbons, effect of high magnetic field on the martensitic transition and magnetoresistive properties has also been studied. The application of magnetic field is found to stabilize the austenite phase.
Thermomagnetic properties and magnetocaloric effect (MCE) in Ni 50.3 Mn 36.5 Sn 13.2 Heusler alloy ribbons are reported. Large magnetocaloric response has been obtained for l 0 H = 3 T in both the reversible adi-abatic change in temperature DT ad (À6.3 and +4.7 K) and the isothermal change in the total entropy DS T (+11.8 and À2.2 J K À1 kg À1), respectively at the temperature T str = 271 K at which the magnetostruc-tural phase transition from the low-temperature Martensite phase (MP) to the high-temperature Austen-ite phase (AP) takes place, and at T CA = 311 K at which the magnetic phase transition in the AP occurs. The MCE has been studied through the Stoner's magnetocaloric parameter n S (Stoner EC. Phil Mag 19 (1935) 565), and a generalized expression for the equations of state for magnetic materials is presented. The phase coexistence of the MP and AP has been studied via their respective sublattice with opposite-aligned magnetic moments by means of the effective magnetic anisotropy density e A induced by the supercooled (superheated) secondary AP (MP) in the MP (AP). Magnetic fields higher than the critical value of l 0 H R = 0.5 T produce alignment of the two magnetic moments and hence a change in the magnetic ordering in the MP from antiferromagnetic to ferromagnetic, resulting in a thermomagnetic behavior in which the field-cooling and field-heating magnetizations become coincident, the induced anisotropy vanishes e A = 0 and the metastability disappears. New tentative methods to obtain the spontaneous magnetization of both MP and AP and their respective fractions in the phase coexistence range are reported.
Annealing Effect on Structural and Magnetic Properties of Cu 2 MnAl Heusler Alloy Films
Journal of Superconductivity and Novel Magnetism
Cu2MnAl Heusler alloy films were grown on MgO (001) substrates by using the ion beam sputtering technique. The films were post-annealed at varying temperatures in order to investigate the influence of annealing on crystal structure and magnetic properties. The structural properties of Cu2MnAl films have been investigated by using x-ray diffraction (XRD) and magnetic properties have been investigated by both vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. The experimental data indicates that the crystal structure of the films strongly depends on the annealing temperature. When the films were annealed at 200 °C, the saturation magnetization (M s =250 emu/cm3) achieved its maximum and the coercive field (H c ≈7 Oe) reached its minimum with B2 ordered structure. In addition, FMR results have revealed that the Cu2MnAl film annealed 200 °C has the highest effective magnetization. The combination of structural and magnetic characterization indicates that the optimum growth temperature is 200 °C for the Cu2MnAl Heusler alloy films on MgO substrates.
Magnetic and transport properties of Cu 2MnAl Heusler alloy prepared by rapidly quenched method
Journal of Magnetism and Magnetic Materials, 2007
The Cu 2 MnAl alloy was prepared by rapidly quenched (suction-casting and melt-spinning) methods with various thicknesses of 20, 40 and 1000 mm. The X-ray diffraction (XRD) patterns of the fabricated samples show a single phase of Cu 2 MnAl. All the samples reveal soft magnetic behavior with coercivity below 1.6 kA/m and Curie temperature of about 600 K. Resistance of the alloy behaves as a linear function of applied magnetic field. Magnetoresistance (MR) ratio depends on the thickness of the samples and achieves $0.8% at the field of 240 kA/m for the sample with thickness of 20 mm. The variation of the properties of the alloy can be interpreted by the difference of energy band structure caused by defects in the alloy. r
IEEE TRANSACTIONS ON MAGNETICS, 2018
Structural, electronic and magnetic properties of the Heusler alloy Mn 2 VIn have been investigated using the density functional theory and experimental techniques. Unlike many other Heusler compounds, Mn 2 VIn is not predicted to be half-metallic at the optimized lattice constant, but is highly spin polarized at a slightly lower lattice constant. It however exhibits ferrimagnetic coupling between the Mn and V sublattices, as expected of Mn-based Heuslers. We have, then, synthesized the compound by arc melting and studied magnetic properties that are of interest fundamentally and for technological applications. The structural properties were determined using X-ray diffraction, revealing the presence of cubic and tetragonal phases in the sample. The chemical composition was determined using energy-dispersive X-ray spectroscopy together with the scanning electron microscope, and the magnetic properties were investigated by superconducting quantum interference device magnetometry. The alloy exhibits superparamagnetic spin blocking with a blocking temperature T B of 40 K.
Journal of Superconductivity and Novel Magnetism, 2019
Magnetism, electronic structure, elastic and thermal properties of Mn 2 YAl (with Y = Cr, V) have been investigated. The optimized lattice parameters, bulk modulus, and cohesive energy have been obtained. These alloys have the ferrimagnetic state as the most stable magnetic configuration, since the calculations showed a strong Mn-V antiferromagnetic coupling leading to the ferromagnetism of the Mn sublattices. A small and itinerant magnetic moment of Mn at the A site is found, which is antiparallel to the moment of Y at the B position in Mn 2 YAl (with Y = Cr, V) compounds. The calculated total spin moments are integral values and increase from − 2 μ B /f.u. for Mn 2 VAl to-1 μ B /f.u. for Mn 2 CrAl with increasing the number of valence electrons. Band structure and total and partial density of states could be calculated via applying the modified Becke Johnson approximation (mBJ). Based on these results, Mn 2 YAl (with Y = Cr, V) are half-metallic ferrimagnets with the energy gap lies in the majority spin direction and a high-spin polarization (100%). The main difference between these two compounds is that the band gap is increased by 48% (0.210 eV for Mn 2 CrAl and 0.401 eV Mn 2 VAl). Elastic anisotropies, brittleness, and thermodynamic properties are determined for the Mn 2 YAl (with Y = Cr, V). The slight difference in the spatial distributions of Young's moduli of Mn 2 YAl (with Y = Cr, V) reflects the small differences for the elastic anisotropies of the alloys under consideration. The mechanical stability of Mn 2 YAl (with Y = Cr, V) alloys are studied based on the elastic constants. The thermal properties are studied and investigated using the quasi-harmonic model, in addition, the temperature effect on heat capacities at constant pressure and volume, entropy, and thermal expansion are analyzed and discussed.
Magnetic interactions in martensitic Ni-Mn-based Heusler systems
2010
In this work, magnetic, magnetocaloric and structural properties are investigated in Ni-Mn-based martensitic Heusler alloys with the aim to tailor these properties as well as to understand in detail the magnetic interactions in the various crystallographic states of these alloys. We choose Ni 50 Mn 34 In 16 as a prototype which undergoes a martensitic transformation and exhibits field-induced strain and the inverse magnetocaloric effect. Using the structural phase diagram of martensitic Ni-Mn-based Heusler alloys, we substitute gallium and tin for indium to carry these effects systematically closer to room temperature by shifting the martensitic transformation. A magneto-calorimeter is designed and built to measure adiabatically the magnetocaloric effect in these alloys.
Structural and Magnetic Transitions in Rapidly Solidified Heusler Alloys Ribbons
Solid State Phenomena, 2009
The most extensively studied Heusler alloys are those based on the Ni-Mn-Ga system. However, to overcome the high cost of Gallium and the usually low martensitic transformation temperature, the search for Ga-free alloys has been recently attempted, particularly, by introducing In, Sn or Sb. In this work, Mn 50 Ni 40 In 10 , Mn 50 Ni 34 In 16 , Ni 50 Mn 36-x In 14+x (x = 0, 0.5, 1, 1.5) and Ni 50 Mn 37 Sn 13 ribbons has been obtained by melt spinning. We outline their structural and thermomagnetic behavior. Columnar grains and preferential orientation has been obtained. The martensitic, T m , and the Curie, T C , temperatures of the ribbons are lower than those of the bulk samples with similar compositions. This effect is probably due to the ribbons small and constrained grains. For it, a large under-cooling is necessary for the martensitic transformation. The decrease of T C in the ribbons could be associated with the increased degree of quenched-in short-range disorder around defects.
We report features of microstructure, martensitic transformation, magnetic properties and magnetoca-loric effect in three off-stoichiometric Ni 45 Mn 44 In 11 , Ni 47 Mn 41 In 12 and Ni 48 Mn 39 In 13 (nominal-compositions) alloys ribbons. They were selected in the 7.8o e/ao 8.0 range, being e/a the valence electron concentration per atom, one of the parameters that determines functional properties displayed by these alloys near room-temperature. Although the real composition is shifted from nominal one in each sample, its influence on all here studied properties at the temperature range of 50–400 K is analyzed. Especially, the role played by Ni content in the decrease of magnetization observed in two alloys with respect to the third one with the lowest e/a. Ni content effect on the antiferromagnetic interaction present in the martensitic phase of the alloys ribbons is also evidenced.
Phase transition and magnetocaloric properties of Mn50Ni42−x Co x Sn8 (0 ≤ x ≤ 10) melt-spun ribbons
IUCrJ, 2018
The characteristics of magnetostructural coupling play a crucial role in the magnetic field-driven behaviour of magnetofunctional alloys. The availability of magnetostructural coupling over a broad temperature range is of great significance for scientific and technological purposes. This work demonstrates that strong magnetostrucural coupling can be achieved over a wide temperature range (222 to 355 K) in Co-doped high Mn-content Mn 50 Ni 42Àx Co x Sn 8 (0 x 10) melt-spun ribbons. It is shown that, over a wide composition range with Co content from 3 to 9 at.%, the paramagnetic austenite first transforms into ferromagnetic austenite at T C on cooling, then the ferromagnetic austenite further transforms into a weakly magnetic martensite at T M. Such strong magnetostructural coupling enables the ribbons to exhibit field-induced inverse martensitic transformation behaviour and a large magnetocaloric effect. Under a field change of 5 T, a maximum magnetic entropy change ÁS M of 18.6 J kg À1 K À1 and an effective refrigerant capacity RC eff of up to 178 J kg À1 can be achieved, which are comparable with or even superior to those of Ni-rich Ni-Mn-based polycrystalline bulk alloys. The combination of high performance and low cost makes Mn-Ni-Co-Sn ribbons of great interest as potential candidates for magnetic refrigeration. research papers IUCrJ (2018). 5, 54-66 Zongbin Li et al. Magnetocaloric properties of Mn 50 Ni 42Àx Co x Sn 8 55