Alloy NiMnSb Research Articles

Shape Memory Materials Based on a NiMnSb Alloy and Polylactic Acid/Polyhydroxyalkanoate: Evaluation of The Chemical And Physical Properties

AbstractIn this study, NiMnSb alloy and PLA/PHA blend composite films with shape memory properties, which exhibit magnetic, elastic, and smart properties at the same time, were prepared by solution casting method. After the magnetic shape memory alloy (MSMA) used in different ratios was doped into the polymer, its effect on the characteristic functional groups of PLA and PHA was examined by attenuated total reflectance‐infrared spectroscopy (ATR‐IR). When the thermal data were examined, it was determined that as the NiMnSb ratio increased, the percentage residue amount increased and the highest residue amount at 500 °C was in the PLA/PHA blend composite film containing 20 % alloy. In X‐ray diffraction (XRD), it was observed that the characteristic signal of the NiMnSb alloy in polymer blend composite films became evident with increasing concentration at 2θ=45° (222). VSM results showed that when a ferromagnetic material such as NiMnSb was doped into the diamagnetic PLA/PHA blend film, the resulting composite now showed ferromagnetic properties. In addition, it has been determined that MSMA further improves this feature of the PLA/PHA blend, which has a shape memory effect.

Microstructural evolution and phase stability in semi-Heusler NiMnSb and vanadium added equi-atomic NiMnSbV alloys

Phase and microstructure evolution in semi-Heusler NiMnSb and vanadium added quaternary equi-atomic NiMnSbV alloys has been studied in the as solidified state. In the as solidified NiMnSb alloy, cubic semi-Heusler phase and in the as solidified NiMnSbV alloy, Frank-Kasper type cubic SbV3 phase along with the cubic semi-Heusler NiMnSb phase are observed. Nucleation and growth of SbV3 phase takes place in the alloy through solute rejection mechanism, and at the interface of SbV3 and NiMnSb semi-Heusler phase, lamellar structure is observed. While SbV3 phase is stable upto 700 °C, the semi-Heusler NiMnSb phase is not stable beyond 400 °C and it transforms to hexagonal (Ni/Mn)Sb phase. Line defects are observed in the NiMnSb semi-Heusler phase. However, extensive twin like defects are observed in the cubic SbV3 phase. In the SbV3 phase edge sharing 12-fold coordinated icosahedral clusters and 14-fold coordinated clusters are present. Atomic size difference of Sb and V indicates that the clusters are distorted, which might be the viable cause behind the formation of such kind of compound deformation twins. The phase formation and stability in these two alloys has been studied through Miedema’s model. It is observed that apart from atomic size difference, enthalpy of mixing; the ternary and higher order self-interactions, electronic contribution to enthalpy also play an important role. Systematic substitution in the lattice of semi-Heusler NiMnSb phase based on enthalpy of mixing and atomic radius may not be the design strategy for development of semi-Heusler NiMnSb based single phase multicomponent/high entropy alloys.

Nanoscale-Thick Ni-Based Half-Heusler Alloys with Structural Ordering-Dependent Ultralow Magnetic Damping: Implications for Spintronic Applications

Atomic ordering and its consequence on the crystal structure are fundamental issues in the application of half-metallic Heusler alloys considered as a high spin-polarized electron source. NiMnSb is a promising half-metallic half-Heusler alloy for spintronic devices due to its low magnetic damping, non-centrosymmetric crystal structure, and rich anisotropies. Here, we report a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate. High temperature deposition is a crucial parameter for crystal growth and magneto-dynamic properties such as damping, anisotropy, magnetization, etc. After investigating the ferromagnetic resonance (FMR) spectroscopy using a time-resolved magneto-optical Kerr (TRMOKE) microscope and calculating the crystal structure using VESTA and the density of states from first-principles calculations, we discuss how the deposition temperature influences the crystal ordering, damping, and magnetization. Ultralow Gilbert damping with high anisotropic field and saturation magnetization were found for the highly ordered C1b structured nano-scale thick NiMnSb film deposited at 573 K. We also found quite nice agreement between theoretical and experimental data of crystal ordering and damping that explains how the ordering affects the magnetic parameter as well as sample quality. Furthermore, the negative anisotropic magnetoresistance ratio implies the robust bulk half-metallicity. Such unique combination of highly ordered half-metallic NiMnSb alloy in the nano-scale regime with ultralow damping can be regarded as an advantage for applications in spintronic devices.

Electrical transport with temperature-induced spin disorder in NiMnSb

Abstract We investigate theoretically the combined effect of phonons and magnons caused by finite temperatures on the electrical resistivity of nonstoichiometric half-Heusler NiMnSb alloy. The coherent potential approximation within the alloy analogy model is employed for an efficient treatment of chemical impurities, atomic displacements, and magnetic disorder. Spin fluctuations of local Mn moments are described by two models: (i) uncompensated disordered local moment approach and (ii) tilting of the moments. The calculated resistivity agrees with experimental data, the agreement is good up to 600 K. We show that a strong magnetic disorder leads to a violation of the Matthiessen’s rule for the resistivity. We also discuss the spin polarization of the electrical current which exceeds 90% at room temperature but it is dramatically reduced by the magnetic disorder for higher temperatures approaching the Curie point ( T C = 730 K).

Microstructural and Crystallographic Insights in a Martensite/Austenite Dual Phase Ni–Mn–Sb Alloy

For Ni–Mn–Sb multifunctional alloy, its microstructure and crystallographic information are decisive factors for its multiple magnetic field induced properties, such as magnetic field induced shape memory effect, magneto‐caloric effect, exchange bias effect, and so on. While, studies on such field are rarely conducted. In the present work, a thorough study on microstructural features and crystallographic characteristics has been conducted in a martensite/austenite dual phase coexisting polycrystalline Ni50Mn37Sb13 alloy. Results show that the martensite is self‐organized in plates in the original austenite. The intra‐plate martensite presents a fine lamellar microstructure and each fine lamella corresponds to one martensite variant. Crystallographic orientation analysis indicates that each martensite plate exists four differently oriented martensite variants and they can form three types of twins, type I, type II, and compound twin. Trace analysis results show that the interface between adjacent variants are their twinning plane K1. Further investigation on martensitic transformation orientation relationship reveals that the Pitsch orientation relationship, specified as //and //, is the effective one from austenite to martensite. All the above results offer basic microstructural and crystallographic information on Ni–Mn–Sb alloys and can be useful for further investigation on property optimization of these alloys.

Enhanced current-perpendicular-to-plane giant magnetoresistance effect in half-metallic NiMnSb based nanojunctions with multiple Ag spacers

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) heterostructure devices using half-metallic NiMnSb Heusler alloy electrodes with single, dual, and triple Ag spacers were fabricated. The NiMnSb alloy films and Ag spacers show (001) epitaxial growth in all CPP-GMR multilayer structures. The dual-spacer CPP-GMR nanojunction exhibited an enhanced CPP-GMR ratio of 11% (a change in the resistance-area product, ΔRA, of 3.9 mΩ μm2) at room temperature, which is approximately twice (thrice) of 6% (1.3 mΩ μm2) in the single-spacer device. The enhancement of the CPP-GMR effects in the dual-spacer devices could be attributed to improved interfacial spin asymmetry. Moreover, it was observed that the CPP-GMR ratios increased monotonically as the temperatures decreased. At 4.2 K, a CPP-GMR ratio of 41% (ΔRA = 10.5 mΩ μm2) was achieved in the dual-spacer CPP-GMR device. This work indicates that multispacer structures provide an efficient enhancement of CPP-GMR effects in half-metallic material-based CPP-GMR systems.

Crystal structure and crystallographic characteristics of martensite in Ni50Mn38Sb12 alloys

For Ni–Mn–Sb ferromagnetic multifunctional alloys, the crystal structures of martensite variants and the orientation relationships between them are decisive factors for their magnetic field-induced behaviours and are hence of importance. Such information has rarely been reported in the literature. In the present work, the crystal structure, microstructure and orientation relationships of Ni–Mn–Sb martensite were thoroughly investigated by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Through XRD analyses, the crystal structure of the martensite, including the crystal system, the space group, the lattice parameters and the atomic coordinates, was fully resolved. The structure is orthorhombic and can be represented with a 4O superstructure. EBSD analyses show that the Ni–Mn–Sb martensite has a lamellar form. One martensite lamella corresponds to one orientation variant. The lamellae are organized in long plate-shaped colonies. Within each colony, four distinct orientation variants (A, B, C and D) appear repeatedly and extend in roughly the same direction. The four variants are twin related to one another, with variants A and C (or variants B and D) forming a type I twin, variants A and B (or C and D) a type II twin, and variants A and D (or B and C) a compound twin. The complete twinning elements for each twin relation were thus fully determined. The interfaces between the variants were identified to be their corresponding twinning planes. All these results provide fundamental information for Ni–Mn–Sb alloys that is useful for interpreting their magnetic and mechanical characteristics.

Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films

The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic resonance (FMR) measurements and calculations from first principles to investigate how the composition of the epitaxially grown NiMnSb influences the magnetodynamic properties of saturation magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$. $M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while the Gilbert damping is minimum. We find excellent quantitative agreement between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows the same trend as the experimental data, but has a larger magnitude. Additionally to the unique in-plane anisotropy of the material, these tunabilities of the magnetodynamic properties can be taken advantage of when employing NiMnSb films in magnonic devices.

Transport and magnetic properties of Heusler alloy Ni–Mn–Sb prepared by solid state microwave heating

In this study, Heusler alloy [Formula: see text] has been prepared by solid state hybrid microwave heating within 40 min. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses reveal that the obtained samples are of single phase cubic structure and homogeneous. Temperature-dependence of electrical resistivity and magnetization measurements confirm the austenite to martensitic transition of the first-order nature with the absence of the exchange bias (EB), which is verified by the magnetic hysteresis loops. Compared with the samples prepared by conventional arc-melting method, the sample synthesized by fast microwave heating has lower martensitic transition temperature, smooth magnetization change in the martensitic region and disappeared EB, implying strongly suppressed antiferromagnetic (AFM) interaction. These results suggest that tuning the microstructure via different synthesis method can influence significantly the martensitic transition and magnetic interactions in the Ni–Mn–Sb system.

Martensitic phase transformations and magnetocaloric effect in Al co-sputtered Ni–Mn–Sb alloy thin films

Abstract We systematically investigated the influence of aluminium (Al) content on the martensitic transformations and magnetocaloric effect (MCE) in Ni–Mn–Sb ferromagnetic shape memory alloy (FSMA) thin films. The temperature-dependent magnetization (M–T) and resistance (R–T) results displayed a monotonic increase in martensitic transformation temperature (TM) with increasing Al content. From the isothermal magnetization (M–H) curves, a large magnetic entropy change (ΔSM) of 23 mJ/cm3 K was observed in N49.8Mn32.97Al4.43Sb12.8. A remarkable enhancement of MCE could be attributed to the significant change in the magnetization of Ni–Mn–Sb films with increasing Al content. Furthermore, a high refrigerant capacity (RC) was observed in Ni–Mn–Sb–Al thin films as compared to pure Ni–Mn–Sb. The substitution of Al for Mn in Ni–Mn–Sb thin films with field induced MCE are potential candidates for micro length scale magnetic refrigeration applications where low magnetic fields are desirable.

Fate of half-metallicity near interfaces: the case of NiMnSb/MgO and NiMnSi/MgO.

The electronic and magnetic properties of the interfaces between the half-metallic Heusler alloys NiMnSb, NiMnSi, and MgO have been investigated using first-principles density-functional calculations with projector augmented wave potentials generated in the generalized gradient approximation. In the case of the NiMnSb/MgO (100) interface, the half-metallicity is lost, whereas the MnSb/MgO contact in the NiMnSb/MgO (100) interface maintains a substantial degree of spin polarization at the Fermi level (∼60%). Remarkably, the NiMnSi/MgO (111) interface shows 100% spin polarization at the Fermi level, despite considerable distortions at the interface, as well as rather short Si/O bonds after full structural optimization. This behavior markedly distinguishes NiMnSi/MgO (111) from the corresponding NiMnSb/CdS and NiMnSb/InP interfaces.

Effect of high-temperature quenching on the magnetostructural transformations and the long-range atomic order of Ni–Mn–Sn and Ni–Mn–Sb metamagnetic shape memory alloys

The influence of high-temperature thermal treatments on the martensitic transformation and the magnetic properties of Ni–Mn–Sn and Ni–Mn–Sb metamagnetic shape memory alloys have been investigated by calorimetric and magnetic measurements. Contrary to Ni–Mn–Ga and Ni–Mn–In systems, the martensitic transformation and Curie temperatures of Ni–Mn–Sn and Ni–Mn–Sb alloys are found to be unaffected by the increasing quenching temperature. Neutron diffraction measurements confirm the null effect of quenching on the next-nearest-neighbors atomic order due to the negligible L21 atomic disorder achieved with high-temperature annealings. The analysis of long-range order also suggests that no L21–B2 ordering transition takes place in the studied alloys, thus indicating an unusually high stability of the L21 structure. The obtained results show that the magnetostructural properties of Ni–Mn–Sn and Ni–Mn–Sb alloys cannot be properly tuned by means of standard thermal treatments.

Stability of ferromagnetism against doping in half-metallic alloys

We use a rigid band model to simulate doping in half-metallic NiMnSb and CoMnSb semi-Heusler alloys. Using first-principles calculations we calculate the intrasublattice exchange constants and the Curie temperature for these alloys as a function of the shift of the Fermi level and compare them also with the case of half-metallic CrAs and CrSe zinc-blende alloys. We show for all four compounds that the interactions between Cr-Cr(Mn-Mn) nearest neighbors are sufficient to explain the behavior of the Curie temperature. The interplay between the ferromagnetic RKKY-like and the antiferromagnetic superexchange interactions depends strongly on the details of the density of states around the minority-spin gap and thus it is found to be alloy-dependent.

First-principles study of magnetism and electronic structureof Sb-containing half-Heusler alloys

Using the first-principles density functional theory, we calculate the crystal structures, magnetisms and electronic structures of Sb-containing half-Heusler alloys XYSb(X=Ni, Pd, Pt; Y=Mn, Cr). The calculation results show that alloy NiMnSb is half-metal and the others are metals at equilibrium lattice constant. The contribution of the spin magnetic moment of Y element to the total moment is largest for all alloys. It is found that the Fermi level of the minority spin band shifts closer to the bottom of spin-down conduction band with atomic number of X element reducing. The Fermi level moves up due to the compressive strain, away from p bands of Sb atom. Under the compresive stress, PtMnSb, PdMnSb and NiCrSb can induce metal half-metal transitions.

Tilted elliptical Dirac cones at a half-metal surface

The surface electronic structure of the half-metallic alloy NiMnSb is investigated in detail, revealing the presence of Dirac cones in the minority-spin states. Surface-localized carriers of suitable energy will consequently behave as massless Dirac fermions, a remarkable situation for a half-metallic material and potentially of great significance in future spintronic device applications. Unlike related features observed previously in graphene and at the surfaces of topological insulators, the Dirac cones described here are of elliptical cross section and are tilted with respect to the energy axis. Such unique properties are permitted due to the lower symmetry in the present case.

Electronic structure of the NiMnSb-semiconductor (110) interface

The electronic structure and magnetic properties of the (110) interface between the half-metallic Heusler alloy NiMnSb and semiconductors with different configurations of contact atoms have been calculated in terms of the density functional theory. It has been shown that spin polarization depends substantially on the configuration of atoms at the contacts. The nature of the interface states at the contacts under consideration has been analyzed. A nearly 100% spin polarization is obtained for the configuration with nickel and antimony, which in the alloy occupy the corresponding sites of the anion and the cation in the semiconductor. The evaluation of the adhesion energy at the interfaces has demonstrated that contacts with a maximum spin polarization also have the highest energy and are energetically favorable and stable.

Electronic structure and spin polarization at the NiMnSb/GaAs(110) interface

Within the density functional theory, ab initio calculations of the electronic structure and magnetic properties of the (110) interface between the NiMnSb alloy and GaAs in dependence on configuration of contact atoms are carried out. It is found that two out of six possible atomic configurations of the interface exhibit a high degree of spin polarization, which attains 100% for one of the interfacial structures studied here. It is shown that contacts with a high degree of spin polarization are the most stable with an adhesion energy of about 1.3 J/m2.

Effect of chemical disorder on NiMnSb investigated by appearance potential spectroscopy: an experimental and theoretical study

The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with unique properties for future applications. Band structure calculations exclusively predict majority bands at the Fermi level, thus indicating 100% spin polarization there. For the development of functional materials, chemical disorder has to be considered quantitatively. The magnetization, spin polarization and electronic structure are expected to be sensitive to structural and stoichiometric changes. We studied the influence of chemical disorder on the unoccupied electronic density of states of NiMnSb(0 0 1) by the use of the ab initio coherent potential approximation method and results are discussed along with corresponding measurements.

Phase coexistence, microstructure and magnetism in Ni–Mn–Sb alloys

We present here a detailed investigation on the structural and magnetic transformations in the Ni50Mn50−xSbx Heusler alloys with composition x = 12, 13 and 14. The evolution of martensitic to austenitic transformation has been investigated using temperature dependent x-ray diffraction study. A wide region of phase coexistence is observed across the martensitic transformation. The unit cell volume contracts by 0.82% and 0.74% for x = 12 and 14, respectively, at the martensitic transformation temperature. The martensitic transition temperature decreases with increase in Sb concentration. The magnetic interactions in the martensitic and austenitic phases are found to be ferromagnetic, however, with different strengths, giving rise to two separate magnetic transitions with . The magnetization studies reveal the presence of antiferromagnetic–ferromagnetic interactions in the alloys. Exchange bias blocking temperature has been observed around 100 K for the alloy x = 12. Magnetic field induced structural transition has been observed in x = 14 alloy, in which the structural transition temperature shifts by 25 K in a field of 3 T.

Optical absorption and magnetooptical effects in the Heusler alloy NiMnSb

Optical and magnetooptical properties of the Heusler alloy NiMnSb, which refers to the class of half-metallic ferromagnetic materials, have been investigated. The temperature dependence (T = 80−480 K) of the diagonal component of the tensor of dielectric constant \( \hat \varepsilon \) in the spectrum range of ℏω = 0.5–5.0 eV has been studied under conditions of ultrahigh vacuum P ∼ 10−8 Pa. In the range of photon energies ℏω = 0.18–4.8 eV, measurements of the transverse Kerr effect have been performed and the dispersion of the off-diagonal component of the dielectric-constant tensor \( \hat \varepsilon \) has been determined. It has been established that in the region of the fundamental band of interband absorption (ℏω = 1–5 eV) the spectral dependence of the diagonal and off-diagonal components of the tensor \( \hat \varepsilon \) can be satisfactorily explained on the basis of existing information on the electronic structure of NiMnSb. The differences between the experimental and theoretical curves are only observed in the IR range of the spectrum. At the photon energies E < 1 eV, contributions from interband electron transitions have been revealed in the optical absorption and magnetooptical characteristics, which indicate the existence of low-energy gaps ΔE ∼ 0.07–0.8 eV in the vicinity of the Fermi level EF in the energy-band spectrum of NiMnSb. The results obtained support the concept of the formation of a pseudo-gap at EF in the density of states of electrons with spins opposite to the direction of spontaneous magnetization. For the first time, a magnetooptical effect quadratic in magnetization has been revealed in NiMnSb and its spectral dependence has been studied.