L21-type Structure Research Articles

The structure, magnetism and mechanical properties of L21-type full-Heusler alloy Cr2ZrSi: A first-principles study

Heusler alloy is a widely studied spintronic material in recent years, which has played a huge role in the field of spintronic devices due to its high spin polarization and high Curie temperature. Using first-principles calculation to predict the basic properties of Heusler alloy can not only save experimental costs and time but also provide a reliable theoretical basis for experimental research. This study used a first-principles calculation to study the magnetic and mechanical properties of full-Heusler alloy Cr2ZrSi with an L21-type structure. The research results indicate that the alloy is a half-metallic ferromagnetic material with a theoretical value of 100% spin polarization. The magnetism mainly comes from the asymmetric spin contribution of d-orbital electrons of transition metal atoms and their hybridization. At the same time, this complex hybridization coupling process is also a possible reason for the half-metallic band gaps. In terms of mechanical properties, the Cr2ZrSi alloy exhibits good ductility and anisotropy, with a Debye temperature of 303.848K. Our theoretical research results provide more choices and theoretical basis for subsequent experimental research.

Fe-Ni based alloys as rare-earth free gap permanent magnets

L10-ordered FeNi phase has potential as a rare-earth free permanent magnet due to its large magnetization and high Curie temperature. However, low long-range crystal ordering and weak magnetocrystalline anisotropy (Ku) impede its practical use in a technologically relevant permanent magnet. Employing density functional and Monte Carlo simulations, we demonstrate the substantial improvements on structural and thermal stability, disorder-order phase transition, and intrinsic permanent magnetic properties of Fe−Ni structures. We propose that this is achievable through the complementary elemental substitutions by metal elements (M) and interstitial doping with 2p elements. Fe1-xMxNi with simple metal (M = Ga and Al) and metalloid (M = Ge and Si) elemental substitutions at x = 0.5 are broadly known as Heusler (L21) structures with no permanent magnet characteristics. On the contrary, we find that for x = 0−0.5, L10-type structure is energetically favored over the Heusler-type structures. The predicted structures exhibit Ku values up to approximately 2.1 MJ/m3, which is roughly three times that of FeNi phase (0.68 MJ/m3), where the absolute value of Ku depends on the degree of L10 crystal ordering. Interstitial doping with B elevates Ku further up to a maximum value of 3.9 MJ/m3 (at 0 K), leading to room-temperature intrinsic permanent magnetic properties, including maximum energy density product (BH)max, anisotropy field μ0Ha, and hardness parameter κ, comparable to the widely investigated MnBi and MnAl permanent magnets. These results may serve as a guideline in designing Fe−Ni based rare-earth free gap permanent magnetic materials that were previously overlooked.

Magnetic properties of the off-stoichiometric Heusler alloys Rh2Mn1+xSn1-x

We report the results of experimental investigation of the crystal structure, magnetization and 119Sn Mössbauer spectroscopy of Rh2Mn1+xSn1-x (0 ≤ x ≤ 0.6). The samples crystallize in the cubic L21-type structure for 0 ≤ x ≤ 0.4 and the cubic B2-type structure for x = 0.5 and 0.6. X-ray diffraction patterns with the samples with 0 ≤ x ≤ 0.4 indicate that the excess Mn atoms occupy the Sn sites. The samples with 0 ≤ x ≤ 0.4 exhibit the typical ferromagnetic behavior. The magnetic moment at 5 K of 4.27 μB/f.u. for x = 0 (Rh2MnSn) initially increases with increasing x and saturates for x ≥ 0.2. On the other hand, the Curie temperature for 0 ≤ x ≤ 0.4 decreases with increasing x. It is presumed that both samples with x = 0.5 and 0.6 are in the heterogeneous magnetic state. The 119Sn Mössbauer spectroscopy measurements showed that the hyperfine field at 90 K for 0 ≤ x ≤ 0.6 increases with increasing x. The concentration dependence of the magnetic moment and the Curie temperature for Rh2Mn1+xSn1-x (0 ≤ x ≤ 0.6) are discussed qualitatively based on the Mn-Rh and Mn-Mn interactions in the crystal.

Magnetic and crystallographic properties of Heusler alloy Ni2Mn1.48Sn0.52

The results of experimental investigations of the crystal structure and magnetization of the magnetic shape memory alloy Ni2Mn1.48Sn0.52 are reported. This alloy undergoes the martensitic transition from the cubic L21-type structure to the orthorhombic 4O-type one with decreasing temperature. The Curie temperature TCA in the austenite phase is 310 K. The magnetic state just below the martensitic transition temperature TM is the low magnetization state or something like that. With further decrease of temperature, this alloy regains the ferromagnetism. The unit cell volume contracts discontinuously at TM with decreasing temperature. The percentage of the volume change was estimated to be ∼0.7%. The nearest neighbor Ni–Mn and Mn–Mn distances in both austenite and martensite phases of Ni2Mn1.48Sn0.52 were estimated using the X-ray diffraction analysis. On the basis of the experimental results, the magnetic properties of Ni2Mn1.48Sn0.52 are discussed.

Interatomic orbital hybridization determined structure dependent magnetic behavior in Co-Mn-V-Ga Heusler compounds

Structure-dependent magnetic behaviors and their controlling factor of interatomic orbital hybridization were investigated in Co2-xMnxVGa Heusler compounds. It was found that Mn atoms preferentially occupy the A Wyckoff sites in cubic L21-type structure when x < 1 due to the enhanced covalent hybridization, and then they occupy the remaining C Wyckoff sites. This atomic configuration drives relatively symmetric band filling, which suppresses the magnetic excitation and leads to weakly magnetic states in compounds near the middle composition range. In contrast, when x > 1 in Co2-xMnxVGa, the decreased covalent hybridization results in the increased slope in the composition dependent-lattice parameter curve. The theoretical results are in good agreement with current experimental observations. Interatomic orbital hybridization is also responsible for the phase stability and ductility. This study helps to deeply understand the relation between structural configurations and magnetic properties, and suggests that interatomic orbital hybridization is the key factor influencing structure-dependent magnetism in Heusler compounds.

Constituent contribution to the magnetocrystalline anisotropy in Mn(Al1−xGax)

The phase stability and magnetocrystalline anisotropy (MCA) of tetragonal Mn(Al1−xGax) with the L10-type structure (P4/mmm) has been studied using first-principles density functional calculations. The calculated decomposition energy indicates that partial replacement of Al by Ga suppresses the formation of Mn5(Al,Ga)8 and enhances the thermal stability of the L10 phase while the total magnetic moment per formula unit (f.u.) remains almost unchanged. The site- and atomic-resolved MCA calculations show that the MCA energy (MAE) comes mainly from the Mn atoms, and the total MAE increases from 0.25 meV/f.u. (x = 0) to 0.34 meV/f.u (x = 1). Spin resolved MCA and band structure calculations indicate that the high MCA is mainly due to spin flipping behavior near Fermi level. The derived effective magnetic anisotropy field increases from 37 kOe (x = 0) to 46 kOe (x = 1), in agreement with experiments. Doping with Ga improves the thermal stability of the L10 structure and enhances the magnetic anisotropy field, which facilitates developing high coercivity Mn-Al magnets.

Structural stability, electronic, magnetic, elastic, thermal, thermoelectric and optical properties of L21 and xa phases of Ti2fege heusler compound: GGA and GGA+U methods

ABSTRACT Both L21 and XA type phases ordering of Ti2FeGe compound were investigated based on density functional theory. The structural, magnetic, band structure, density of states, possibility of martensitic transformation, elastic, thermoelectric and optical properties were studied. From the calculated total energy, we noted that L21 type in ferromagnetic state is more stable phase using GGA+U approach. The computed elastic constants of considered compound show that L21 type is ductile, anisotropic and mechanically stable, while the XA phase ordering of Ti2FeGe is not mechanically stable. The (DOS) and band structure of L21 type structure of Ti2FeGe alloy show metallic character in both spin up and spin down directions, while the XA type structure exhibits half-metallic character. Based on quasi-harmonic Debye model applied in the Gibbs program, the lattice vibrational, the bulk modulus, the Debye temperature, the heat capacity, the entropy, the coefficient of thermal expansion and the Grüneisen parameter have also been estimated. The thermoelectric properties of two phases are examined and discussed through consideration of transport coefficients. The optical properties are systematically studied by computing the optical parameters. The obtained results will bring perspective for designing theoretical predictions and experimental studies intended to serve as a reference for future studies on optoelectronic and spintronic applications.

119Sn Mössbauer and magnetization studies of the Heusler alloy Ni2Mn1.48Sn0.52

The results of experimental investigations of the crystal structure, magnetization and Mössbauer spectroscopy of the Heusler alloy Ni2Mn1.48Sn0.52 are reported. The alloy undergoes the martensitic transition from the L21-type cubic structure into 4O-type orthorhombic structure with a thermal hysteresis of ∼23 K. The martensitic transition temperature TM is 309 K. The Curie temperature in the austenitic phase TCA of Ni2Mn1.48Sn0.52 is found to be 316 K. The Mössbauer spectra from the high temperature paramagnetic state at 330 K and the martensitic state at 283 K were both singlets, showing a typical paramagnetic feature in the narrow temperature range just below TM. With further decrease of temperature, the ferromagnetic ordered state also appears in the martensitic phase. The Curie temperature in the martensitic phase TCM is found to be 256 K. Furthermore, the exchange bias effect is observed in the temperature range 1.8 K ≤ T ≤ TB (∼130 K), where TB is an exchange bias blocking temperature. The values of a hyperfine magnetic field at Sn nuclei of Ni2Mn1.48Sn0.52 fall significantly below the molecular magnetic field approximation for S = 1. On the basis of the experimental results, the electronic and magnetic properties of Ni2Mn1.48Sn0.52 are discussed.

The concentration effects on structural and magnetic properties of Fe2V1-xMnxGe Heusler alloys

This study presents the concentration-dependent structural, morphological, and magnetic properties of Fe2V1-xMnxGe Heusler alloys (x = 0.0, 0.25, and 0.50) have not been studied previously in the literature, and are investigated by using X-ray Diffractometer, Scanning Electron Microscope (SEM), and Physical Properties Measurement System (PPMS). We observed from the X-ray diffraction measurements that (except x = 0) Fe2V1-xMnxGe samples have had L21-type crystal structure, matching well with the literature. In all SEM images, some holes and crack-type formations are observed. Increasing Mn content in Fe2V1-xMnxGe Heusler alloys can effectively inhibit grain boundary migration. Except for Fe2VGe, the other alloys in the series are investigated to be soft ferromagnets at 5 K with saturation magnetic moment. The (M-H) graphs especially for Fe2V0.75Mn0.25Ge and Fe2V0.5Mn0.5Ge measured at 5 K reveal almost no coercive fields and easy magnetization. Namely, the system easily saturates without needing any high fields. The obtained results show that these new samples may be suitable candidates for technological applications.

New structure and insight on the phase transition within the Cu-Pd-Sn system with 25 at. % Sn

The Cu-Pd-Sn material system has a (Cu, Pd)3Sn phase region that shows an interesting and unexplored martensitic phase transformation. Literature on this system is limited and the description of the phases present is incomplete and partly contradictory. With focus on a specific Cu-rich composition in this phase region (Cu33Pd42Sn25) and having employed a combination of differential scanning calorimetry, X-ray diffraction, optical microscopy and density functional theory (DFT) methods we analyze the phases involved and the phase transformation temperatures. The martensitic transformation was found to occur at approximately 378 K upon heating and at 328 K under cooling conditions. The crystal structure of the high temperature (HT) austenite phase was identified as face centered cubic with lattice constant a=6.2261(1) Å at 473 K. DFT simulations of plausible atomic arrangements indicated that the HT phase was an L21 (Fm3¯m) type structure. The martensitic LT phase was found to be orthorhombic with a D011 (Pnma) type structure with lattice parameters a = 8.9860(3) Å, b=5.9347(2) Å and c=4.5328(2) Å at 298 K.

Effect of Structural Disorder on the Physical Properties of the Pd Based Heusler Alloys: PdCoMnAl, Pd2CoAl and Pd2MnAl

In this manuscript, we investigate the effect of structural disorder on the physical properties of Pd-based Heusler alloys: PdCoMnAl, Pd2CoAl and Pd2MnAl using first-principles calculations. In fact, we are studying the structural properties of the equatorial quaternary Heusler alloy PdCoMnAl for three phases: type 1, type 2 and type 3, we have carried out this property to determine the most stable phases. The structural properties results show that the phase of type I, of this alloy is the most stable configuration. In addition, the band structures, and density of states calculations results show that this compound exhibits a half-metallic character with a 100% of spin polarization (SP) at the Fermi-level. The total magnetic moment of the Heusler compound is found to be 5.00 µB. Moreover, it is found that the Slater-Pauling is well described for this alloy. On the other hand, concerning total energy of the full Heusler Pd2YAl (Y = Co or Mn) alloys. It is found that such material in L21-type structure is always smaller than in the XA-type structure during the whole lattice variation variety and the L21-type structure is more energetically preferable for the both full alloys. In addition, the density of states at the Fermi level within the spin up and down states show the metallicity of these compounds. Our results show that the quaternary Heusler is a potential candidate for the spintronic applications.

Structure stability driven large magnetocaloric response in Ni–Co–Mn–In–Si Heusler alloy

Ni–Mn–In Heusler alloys have received considerable attention in the field of magnetic refrigeration owing to their eco-friendliness and large magnetocaloric (MC) response. In this paper, samples of Ni45Co5Mn37In12Si1 thus heat-treated for 0 h and 15 h have prepared by means of arc-melting followed by quenching. X-ray diffraction analysis confirms L21-type crystal structure and stabilization of austenite phase at room temperature. FE-SEM equipped with EDS reveals the surface morphology and elemental composition of 15 h heat-treated Ni45Co5Mn37In12Si1 alloy with well-distinguished larger grains and a dendritic structure. Thermomagnetic measurements of 15 h heat-treated Ni45Co5Mn37In12Si1 shows the magnetostructural transition TCM at the temperature of ∼262 K and Curie temperature of austenite, TCA was found to be above ∼396 K with increase in the annealing time. Metamagnetic behavior and magnetic hysteresis are seen in isothermal magnetization curves. Interestingly, a large change in magnetic entropy ΔSM ∼9.3 J kg−1 K−1 was obtained with refrigeration capacity (RC) of ∼416.6 J kg−1 under an applied field change of 5T with a broad temperature window of ∼86 K for Ni45Co5Mn37In12Si1 alloy thus annealed for 15 h which makes it to be suitable for magnetic refrigeration applications.

Elastocaloric and Magnetocaloric Effects Linked to the Martensitic Transformation in Bulk Ni55Fe11Mn7Ga27 Alloys Produced by Arc Melting and Spark Plasma Sintering

The investigation of caloric effects linked to first-order structural transitions in Heusler-type alloys has become a subject of considerable current interest due to their potential utilization as refrigerants in solid-state cooling devices. This study is mainly motivated by the possibility of developing refrigeration devices of improved energy efficiency with a reduced environmental impact. We produced partially textured and isotropic bulk samples of the Heusler-type magnetic shape memory alloy Ni55Fe11Mn7Ga27 by arc melting and spark plasma sintering (SPS), respectively. Their structural, microstructural, and phase transition characteristics and magnetocaloric and elastocaloric effects, associated with first-order martensitic transformation (MT), were studied. The elemental chemical compositions of both samples were close to nominal, and a martensitic-like structural transformation appeared around room temperature with similar starting and finishing structural transition temperatures. At room temperature, austenite exhibited a highly ordered L21-type crystal structure. The partial grain orientation and isotropic nature of the arc-melted and SPS samples, respectively, were revealed by X-ray diffraction and SEM observations of the microstructure. For the arc-melted sample, austenite grains preferentially grew in the (100) direction parallel to the thermal gradient during solidification. The favorable effect of the texture on the elastocaloric response was demonstrated. Finally, due to its partial grain orientation, the arc-melted bulk sample showed superior values of maximum magnetic entropy change (|ΔSM|max = 18.6 Jkg−1K−1 at 5 T) and elastocaloric adiabatic temperature change (|ΔTadme|max = 2.4 K at 120 MPa) to those measured for the SPS sample (|ΔSM|max = 8.5 Jkg−1K−1 and (|ΔTadme|max = 0.8 K).

First-principles calculations to investigate stability, electronic properties and anisotropy of half-metallic full Heusler alloy Co2NbGa

The phase structures, magnetic properties, electronic structures, and anisotropy of the full Heusler alloy Co2NbGa were studied using the first-principles method, and the results were compared with experiments. The L21-type cubic structure was the most stable, which was in good agreement with the experimental measurement. The Curie temperature obtained by the mean field theory was also very close to the experimental value. The electronic structures and magnetic properties showed that the Co2NbGa alloy was a half-metallic ferromagnet with 100% spin polarization at equilibrium, and the robustness of the half-metallic feature was preserved in lattice ranges of 5.79 to 6.42 Å. The Co2NbGa alloy was an anisotropic material with stable mechanical properties at L21-type cubic and XA-type tetragonal structures, and the influence of Hubbard U and vacancy defects on the physical nature was also studied and discussed. The 100% spin polarization, high Curie temperature, and stable equilibrium structure make Co2NbGa alloy a promising candidate in spintronics and magnetoelectronic.

Electronic structure, magnetic properties and martensitic transformation of Ga2MnTM (TM = Sc, Y, Lu) Heusler alloys

The atomic site occupation, electronic structure, magnetism, martensitic transformation of Ga2-based Heusler alloys Ga2MnTM (TM = Sc, Y, Lu) have been investigated by first-principles calculations. For three alloys in cubic phase, the L21-type structure is more stable than XA-type structure, and the magnetic state is ferrimagnetic (FIM) at each equilibrium lattice constant. The total magnetic moments are mainly contributed by Mn atoms due to its strong exchange splitting. For Ga2MnY and Ga2MnLu, the magnetic states between ferromagnetic (FM) state and FIM state alternately appear with increasing crystal constant. Potential martensitic transformation can be gained due to the proper thermodynamic driving force (negative values of ΔE) and c/a, together with the analysis of phonon spectra, by considering the tetragonal distortions of cubic Ga2MnTM (TM = Sc, Y, Lu). The energy minima locate at c/a = 1.29, 1.21, 1.27, respectively. The three alloys in martensitic state show different variations of total magnetic moments and still maintain FIM state with changing c/a. The martensitic transformation and abundant changes in magnetic states motivate researchers to further explore new Z2-based Heusler alloys.

Investigation of martensitic transformation and magnetoresistance properties of cu-substituted Ni-Mn-Sn-B melt spun ribbons

Ni50-xCuxMn38Sn12 + B3% at (x = 0, 1, 3 and 5) melt spun ribbons have been fabricated by melt spinning technique. Structural, electrical and magnetoresistance properties of the ribbons were investigated in this study. It was identified that the austenite phase with the L21 type structure was formed in the ribbons, regardless of composition. Temperature dependence of resistance measurements exhibited the first order martensite transition in the ribbons. The largest negative magnetoresistance (~55%) was obtained at 262 K in the RB1 ribbon. Depending on the Cu-content and magnetic field, a noticeable shift of martensite transition temperature to low temperatures has been clearly observed. From magnetic field dependence of the resistance, it was seen that the resistances dropped sharply with the increase of the applied magnetic field and overlapped near 80 kOe, regardless of temperatures, which strongly indicates the magnetic field-induced martensite-austenite transition.

Effect of hydrostatic pressure on martensitic transformation and low-temperature magnetic properties in Ni45Cu5Mn35In15 Heusler alloy

The effect of hydrostatic pressure on martensitic transformation (MT), superparamagnetic (SPM) and exchange bias (EB) behaviors in polycrystalline Ni45Cu5Mn35In15 has been intensively investigated by various experimental methods. The experimental results show that the studied alloy experiences a MT from the austenitic state with a L21-type cubic structure to the martensitic state with a seven-layer (7 M) modulated orthorhombic structure with decreasing temperature, accompanied by a significant change in magnetization. It is found that applying hydrostatic pressure can induce the MT to occur in the higher temperature, while the Curie transition almost remains unchanged due to the suppression of ferromagnetic (FM) coupling. In addition, the applied hydrostatic pressure can suppress the EB field and coercivity of the studied alloy due to the reduction of the competition between FM and AFM interactions. This phenomenon can be attributed to the fact that the application of hydrostatic pressure reduces the size of the SPM cluster and its average magnetic moment.

First Principle Study on the Electronic, Magnetic and Phase Stability of the Full-Heusler Compound Fe2CuSi

In this study, we have presented a systematic theoretical study about the electronic, magnetic and structural properties of the full-Heusler compound Fe2CuSi based on first principles calculations. The L21-type structure with ferromagnetic configuration is determined to be the ground state. The calculated electronic band structures show metallic behavior for both spin direction and the obtained total magnetic moment of [Formula: see text]B is mostly contributed from the two Fe atoms, which exhibit strong spin splitting effect as revealed from the partial densities of states. Moreover, both mechanical and dynamic stabilities have been accessed and confirmed for Fe2CuSi under its equilibrium ground-state structure. Besides, multiple mechanical parameters have been calculated and they can provide valuable reference for its practical applications. Lastly, we also evaluate the tetragonal phase by introducing tetragonal strain of [Formula: see text] ratio and results show that the cubic phase maintains the lowest total energy throughout the whole studied strain range, even with [Formula: see text] cell volume variations.

Phase Transition and Electronic Structures of All-d-Metal Heusler-Type X2MnTi Compounds (X = Pd, Pt, Ag, Au, Cu, and Ni).

In this work, we investigated the phase transition and electronic structures of some newly designed all-d-metal Heusler compounds, X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni), by means of the first principles. The competition between the XA and L21 structures of these materials was studied, and we found that X2MnTi favors to feature the L21-type structure, which is consistent with the well-known site-preference rule (SPR). Under the L21 structure, we have studied the most stable magnetic state of these materials, and we found that the ferromagnetic state is the most stable due to its lower energy. Through tetragonal deformation, we found that the L21 structure is no longer the most stable structure, and a more stable tetragonal L10 structure appeared. That is, under the tetragonal strain, the material enjoys a tetragonal phase transformation (i.e., from cubic L21 to tetragonal L10 structure). This mechanism of L21-L10 structure transition is discussed in detail based on the calculated density of states. Moreover, we found that the energy difference between the most stable phases of L10 and L21, defined as ΔEM (ΔEM = ECubic-ETetragonal), can be adjusted by the uniform strain. Finally, the phonon spectra of all tetragonal X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) phases are exhibited, which provides a powerful evidence for the stability of the tetragonal L10 state. We hope that our research can provide a theoretical guidance for future experimental investigations.

Designing new tetragonal Heusler materials using V, Cr, Fe and Ni doped Ti2CoGa: A first-principles study

In this work, the structure and potential tetragonal distortion (TD) properties of Ti2CoGa and its M−doped (M = V, Cr, Mn, Fe, Ni) system are studied in detail by first-principles calculations. The result shows that Ti2CoGa alloy should crystalize in cubic L21-type structure and no tetragonal distortion is discovered, which limits its application. Attempts are made to seek new tetragonal Heusler materials by replacing Ti or Co atoms in Ti2CoGa with element M (M = V, Cr, Mn, Fe, Ni). It is found that all the Ti2Co1−xMxGa (x = 0.25, 0.5, 0.75; M = V, Cr, Mn, Fe, Ni) compounds tend to form L21 structure, and only Ti2Co1−xNixGa has the possibility of TD when x > 0.29. For Ti2−xMxCoGa (x = 0.25, 0.5, 0.75) system, the increase of the doping amount results in the cubic ground state of the alloy turning from L21 to XA structure. Furthermore, energy curves with different structures show that the tendency of TD in the alloy can be excited after substitution V (x = 0.29–0.50), Cr (x = 0.31–0.43) and Fe (x = 0.21–0.29) for partial Ti. This research can inspire us to search and realize new tetragonal Heusler materials by suitable doping in ternary Heusler alloys.