Full Heusler Research Articles

Room temperature magneto-caloric effect and electron transport properties study on Ni2.14Mn0.55Sb1.31 alloy

Ni2.14Mnd0.55Sb1.3 Heusler alloy has been prepared by the conventional arc melting method with vacuum-sealed annealing. The sample has been crystallized to Fm3¯m space group in L21 phase, and it is the parent crystal structure of the Ni-based Full Heusler alloy. It has been found that the sample has the Curie temperature (para to ferromagnetic transition temperature) at 290K. It was determined from magnetization ∼ temperature plot (M ∼ T) as well as by employing the Arrott plot method. Also, critical exponent analysis by employing the Arrott plot and Kouvel-Fisher methods confirm that the sample (Ni2.14Mn0.55Sb1.31) obeys mean field theory with long range spin ordering. Analysis of temperature dependent resistivity data interestingly reveals the phonon-phonon and magnon-manon scattering dominance above and below the Curie temperature, respectively. The electrical and magnetic properties investigation endorse that there is a correlation between magnetic and electrical properties of the above sample. The magnetocaloric effect (MCE) analysis is carried out by using the Maxwell’s equations in isothermal magnetization data. It is interesting to note that the sample exhibits maximum MCE near the room temperature (∼290K), i.e., the magnetic Curie temperature. Hence the present alloy may be a potential material to be used for magnetic refrigeration application.

Investigation of the electronic, magnetic, elastic, thermodynamic and thermoelectric properties of Mn2CoCr Heusler compound: A DFT-based simulation

Heusler compounds have been promising materials for their applications in spintronic, memory and thermoelectric devices. The Mn2CoCr, a full Heusler compound, has been investigated here for its mechanical, thermodynamic and thermoelectric prospective for the first time using full potential linearized augmented plane wave (FP-LAPW) method in support of density functional theory (DFT). The estimation of total energy conferred to Fm-3m structure in ferromagnetic phase, which was in accordance to the others finding. The estimated total magnetic moment was found to be 5.02 (in the units of Bohr magneton), which was in accordance with the Pauling-Slater rule and available data. The electronic structure using generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) revealed its metallic nature in both the spin configurations. Further, we have calculated the thermodynamic and thermoelectric constants such as specific heat, Debye temperature, Gruneisen constant, thermal conductivity, Seebeck coefficient and power factor. Our predicted value of specific heat at constant volume is 66.6 J/mol.K at 300 K and 0 GPa, which at higher temperature (1000 K) followed Dulong-Petit limit. The power factor was calculated to be 25x1012 Wm-1K−2 at 500 K, demonstrating its suitability in thermoelectric applications.

Implication of nanostructuring of bulk nanocomposite Ti9Ni7Sn8 on the optimization of high thermoelectric performance

Nanostructuring approach on TiNiSn-based half-Heusler (HH) thermoelectric materials (TE) has been well established as the most prominent paradigm for achieving high figure of merit (ZT). Herein, we have extended this approach on our previously reported bulk nanocomposite (BNC), containing HH and Full Heusler (FH) with little traces of Ti6Sn5 phase in a stoichiometric composition Ti9Ni7Sn8 for the optimization of high thermoelectric performance. A synergistic effect of nanostructuring of Ti9Ni7Sn8 bulk nanocomposite (BNC) on its thermoelectric properties was noticed, revealing an enhanced value of ZT ~ 0.83 at 773 K. This enhancement in ZT value is mainly ascribed to significant reduction in thermal conductivity (κ ~ 1.0 W/mK at 773 K), through modification in grain as well as phase boundary scattering. The marginal enhancement in Seebeck coefficient observed is attributed to charge carrier filtering effect at the interface of HH/FH phases.

The structural, half-metal, magnetic, and mechanical properties of full Heusler alloy CrCoVSb: A first-principles study

In this paper, the Co-mixing calculation of the full Heusler alloy Cr2VSb was performed using a first-principles calculation method. The calculations revealed that, after mixing with Co, the Cr2VSb alloy can form a full Heusler alloy that is a half-metallic magnetic material with an equilibrium lattice parameter of 6.059 Å. Furthermore, the results showed that the magnetic properties of this alloy are mainly derived from the contributions of d electrons associated with the Cr, Co, and V atoms. Stress-induced changes in the lattice parameter had a significant influence on the magnetic moment of each atom, but, owing to mutual compensation, the total magnetic moment of the alloy remained unchanged. In terms of mechanical properties, the results revealed that the CrCoVSb alloy is an anisotropic ductile material.

Giant anomalous Hall and Nernst effect in magnetic cubic Heusler compounds

The interplay of magnetism and topology opens up the possibility for exotic linear response effects, such as the anomalous Hall effect and the anomalous Nernst effect, which can be strongly enhanced by designing a large Berry curvature in the electronic structure. Magnetic Heusler compounds are a promising class of materials for this purpose because they are versatile, show magnetism, and their electronic structure hosts strong topological features. Here, we provide a comprehensive study of the intrinsic anomalous transport for magnetic cubic full Heusler compounds and we illustrate that several Heusler compounds outperform the best so far reported materials. The results reveal the importance of symmetries, especially mirror planes, in combination with magnetism for giant anomalous Hall and Nernst effects, which should be valid in general for linear responses (spin Hall effect, spin orbital torque, etc.) dominated by intrinsic contributions.

Effect of correlation and disorder on the spin-wave spectra of Pd2MnSn, Ni2MnSn , and Cu2MnAl Heusler alloys: A first-principles study

Spin waves, also known as magnons, are low-lying collective excitations in magnetic materials, for which it is hard to achieve agreement between first-principles electronic structure calculations and experiments. It has been shown in literature [I. Galanakis and E. \ifmmode \mbox{\c{S}}\else \c{S}\fi{}a\ifmmode \mbox{\c{s}}\else \c{s}\fi{}\ifmmode \imath \else \i \fi{}o\ifmmode \breve{g}\else \u{g}\fi{}lu, J. Mater. Sci. 47, 7668 (2012)] using as a prototype three full Heusler alloys---${\mathrm{Pd}}_{2}\mathrm{MnSn}, {\mathrm{Ni}}_{2}\mathrm{MnSn}$, and ${\mathrm{Cu}}_{2}\mathrm{MnAl}$---that usual density-functional calculations for perfectly ordered compounds fail by a large margin to reproduce neutron scattering measurements of spin waves. We show for these three compounds that the inclusion of correlation effects in the form of the $\mathrm{GGA}+U$ approach and/or substitutional disorder accounted via the coherent potential approximation affects considerably the calculated magnetic properties and their agreement to the experimental data. We expect our results to pave the way for further studies on magnetic materials for which experimental magnonic data exist.

Structural and Magnetic Properties of Ni1+x MnSb Bulk Heusler Composite Materials.

Variation in structural and magnetic properties with changing valence electron count (VEC) has been studied well in the family of Heusler compounds, while such changes in VEC resulting in half-Heusler (HH) and full-Heusler (FH) composites have not been reported to observe their effect on the magnetic properties. Herein, we have synthesized the composite of HH and FH phases in Ni1+xMnSb (x = 0.0, 0.3, and 0.6) via changing VEC from 22 to 28 in order to investigate the structural and magnetic properties. Interestingly, a transition from half-metallic ferromagnetic to normal ferromagnetic was revealed in Ni1+xMnSb (x = 0.0, 0.3, and 0.6) materials with increasing VEC. The structural investigations of these materials were performed using a X-ray diffraction technique and analyzed by Rietveld Refinement software for all the samples. Rietveld analysis reveals the presence of a significant amount of the NiSb paramagnetic impurity phase in the HH NiMnSb system while in the case of Ni1+xMnSb (x = 0.3 and 0.6), no such impurity phase was observed. Only FH and HH phases in Ni1+xMnSb (x = 0.3 and 0.6) samples were noticed. The magnetic measurement performed on samples employing a vibrating sample magnetometer reveals the ferromagnetic ordering in all samples. A weak hysteresis loop with saturated magnetic moments ∼2.99 and 2.98 μB at room temperature was observed for NiMnSb and Ni1.3MnSb, respectively, while a strong hysteresis loop with lower magnetic moment of 0.88 μB was observed in the Ni1.6MnSb composite. Furthermore, the observed magnetic moments for the composite Ni1.3MnSb have been explained on the basis of the Slater–Pauling rule in relation to VEC.

Soft Ferromagnetic Properties of Half-Metallic Mn2CoAl Heusler Alloy Nanoparticles for Spintronics Applications

The ternary full Heusler alloy Mn2CoAl nanoparticles were synthesized by using co-precipitation technique. The as-prepared sample was observed for amorphous nature and further increased at various annealing temperatures (like 700 °C, 800 °C and 900 °C) in argon gas atmosphere for 5 h. X-ray diffraction studies were performed, and the pattern confirms the formation of Hg2CuTi-type structure of the XA or Xα disorder structure. Williamson-Hall plot (W-H plot) was used to find the uniform deformation model so as to get low value of strain-induced broadening. The presence of Mn2CoAl with the particle size ≈ 50 nm was obtained from high-resolution scanning electron microscopy (HR-SEM), and the elemental analysis study confirms the presence of Mn, Co, and Al. UV-Visible absorption spectrum shows the wide absorption peak at 470 nm and the estimated band gap energy value at Eg = 0.8 eV (from Tauc plot) for 900 °C annealed sample. Synthesized Mn2CoAl nanoparticles induced ferromagnetic behavior due to composition deviation and as a result displayed low coercivity of soft magnetic behavior. Half-metallic ferromagnetic Heusler alloys have a wide range of applications from medical imaging to data storage, and also it has profound spintronics applications.

The half-metallic properties of bulk and the (111), (110) and (001) surfaces for the full Heusler alloy Zr2VIn

Spin polarization and half metallicity are the basic properties of spin electronics devices. The electronic and magnetic characteristics of the CuHg2Ti-kind structure Zr2VIn full Heusler alloy in the bulk and (111), (001) and (110) surfaces are explored using the first-principles investigation based on the density functional theory. The results show that the bulk Zr2VIn alloy achieves a ferromagnetic half-metallic characteristic with an energy gap of 0.3 eV, while the half-metallic characteristic is destroyed at all surfaces. It is noted that this compound shows 100% spin polarization at the Fermi level in the spin-up channel. The current communication also reveals that a total magnetic moment of the Zr2VIn alloy is equal to 2μB. The atomic relaxation of (111), (001) and (110) surfaces of the Zr2VIn compound are also discussed. The Zr(2) atom at (001) surface exhibits the highest spin polarization of 87.79%, a matter that opens the way for several applications related to designing a giant magnetic resistance.

Enhanced Curie temperature and spin polarization in Co-based compounds under pressure: A first principles investigation

In the present study, we report a systematic first principles study which investigates and tunes the percentage of spin polarization in few Co-based full Heusler alloys Co2CrX (X = Al, Ga and In) under hydrostatic strain. At ambient condition, Co2CrAl exhibits half metallic nature while Co2CrGa possesses nearly half metallic nature and Co2CrIn shows metallic nature. Mechanical and dynamical stabilities of all the investigated compounds are confirmed using elastic tensor analysis and phonon dispersion plots respectively at ambient as well as under compression. Hydrostatic compressive strain is applied to all the systems and Co2CrGa turned out to be a half metal at compressive strain corresponding to V/V0 = 0.85 with 100% spin polarization and the percentage of spin polarization for Co2CrIn gets enhanced as a function of compressive strain. Further, an electronic topological transition (ETT) is also observed in Co2CrGa as a function of compressive strain corresponding to V/V0 = 0.85, driving the system towards the half-metallic nature. In addition, ferromagnetic nature of all these compounds is explained by the exchange interactions at both ambient and under compression. Also, the positive pressure dependence of Curie Temperature (TC) as a function of V/V0 for all the compounds is studied and the highest TC = 646.1 K for Co2CrAl is observed under compression corresponding to V/V0 = 0.85.

Magnetic behaviour of Co2MnSi full heusler alloy under pressure and uniaxial strain: a relativistic density functional theory study

We have investigated the electronic structure and magnetic properties of the full-Heusler alloy Co2MnSi (CMS) under external pressures and strains. The total and individual spin and orbital magnetic moments were also obtained under pressures and strains. We found a gradual transition from half-metallic to metallic state around 31 GPa in our relativistic study. The spin polarization degree (SPD) was reduced at the Fermi level by including relativistic effect of spin–orbit coupling. The exchange energy describes the trend of decreasing SPD values. The decreasing behavior observed for individual orbital magnetic moments under applied pressures. The metallic behavior was also observed under 8% strain along [001] direction. It was shown that the SPD values decrease in the presence of spin–orbit coupling, whereas the spin magnetism of Co2MnSi under uniaxial strain is marginally affected.

Anomalous Hall effect in ferromagneticWeyl semimetal candidate Zr1−xVxCo1.6Sn**Project supported by the National Natural Science Foundation of China (Grant Nos. 11774007 and U1832214), the National Key R&D Program of China (Grant No. 2018YFA0305601), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB28000000).

We grew single crystals of vanadium-substituted, ferromagnetic Weyl semimetal candidate Zr1−xVxCo1.6Sn from molten tin flux. These solid solutions all crystallize in a full Heusler structure (L21) while their Curie temperatures and magnetic moments are enhanced by V-substitution. Their resistivity gradually changes from bad-metal-like to semiconductor-like with increasing x while the anomalous Hall effect (AHE), which can be well fitted by Tian–Ye–Jin (TYJ) scaling,[] is also enhanced. Moreover, we find an apparent electron–electron interaction (EEI) induced quantum correction in resistivity at low temperature. The anomalous Hall conductivity (AHC) dominated by the intrinsic term is not corrected.

Impact of annealing temperature on structural and magnetic properties of Co2FeSn Heusler alloy

The Co2FeSn full Heusler alloy nanoparticles were synthesized using co-precipitation method. The as-prepared sample was annealed at various temperatures (700 °C, 750 °C, 800 °C, 850 °C, and 900 °C) for 5hrs in N2 gas atmosphere. The formation of fcc superlattice in L21 disorder structure of the synthesized Heusler alloy was confirmed using x-ray diffraction pattern. The calculated average grain size of prepared Co2FeSn Heusler alloy nanoparticles using Scherrer’s formula was found to be 13 nm. Interpretation of the result obtained, From the VSM measurement, the coercitivity was found to be low (Hc = 340 Oe) indicating the soft ferromagnetic property of the produced alloy.

Electronic structures of 24-valence-electron full Heusler compounds investigated by density functional and GW calculations

The electronic structures of Fe-based and Ru-based full Heusler compounds have been investigated systematically by density functional theory (DFT) with PBE, PBE + U, and HSE06 exchange-correlation (XC) functionals. In order to have a better systematic and quantitative comparison between the results of different approximations, the average deviation of eigenvalues (ADE) between any two electronic band structures were calculated. From quantitative analysis of the ADEs, we have shown that different XC functionals used in the DFT calculations will result in very different and inconsistent electronic band structures. However, the discrepancies are dramatically reduced and get more consistent band structures after the GW calculations. Furthermore, comparing the experimental and calculated Seebeck coefficients and band-gap values of Fe2VAl, it implies that the GW methods including dynamically screened Coulomb interactions are more reliable than DFT with PBE or HSE06 functionals. Conclusively, contrast to the fact that DFT methods give inconsistent band structures when using different XC functionals, the GW methods have better predictive power for the band structures of Fe-based and Ru-based full Heusler compounds.

Interplay of local moment and itinerant magnetism in cobalt-based Heusler ferromagnets: Co2TiSi, Co2MnSi and Co2FeSi

Heusler ferromagnets based on Co are important materials for spintronics. This is due to the exceptional combinations of high Curie temperature and strong spin polarization, including half-metallicity, found in some of these. We investigate the full Heusler compounds, ${\mathrm{Co}}_{2}\mathrm{TiSi}$, ${\mathrm{Co}}_{2}\mathrm{MnSi}$, and ${\mathrm{Co}}_{2}\mathrm{FeSi}$ using first principles calculations. ${\mathrm{Co}}_{2}\mathrm{TiSi}$ and ${\mathrm{Co}}_{2}\mathrm{MnSi}$ are half metals, while ${\mathrm{Co}}_{2}\mathrm{FeSi}$ is not. The trends in the Curie temperatures are reproduced by the calculated spin wave dispersions. Remarkably, ${\mathrm{Co}}_{2}\mathrm{TiSi}$ is a very itinerant magnet but ${\mathrm{Co}}_{2}\mathrm{FeSi}$ and ${\mathrm{Co}}_{2}\mathrm{MnSi}$ show local moment behavior regarding the Fe and Mn, while retaining the itinerancy of the Co magnetism. These materials can therefore be described as itinerant systems with embedded local moment atoms. This provides an explanation for their exceptional behavior. Our results do not support the half-metallic character proposed for ${\mathrm{Co}}_{2}\mathrm{FeSi}$, but they are consistent with a higher Curie temperature relative to the Mn compound. The density of states and transport spin polarizations ${\mathrm{Co}}_{2}\mathrm{FeSi}$ have opposite signs. Importantly, although there is a large minority spin density of states at the Fermi level, leading to a low density of states spin polarization, we find a very strong transport spin polarization in ${\mathrm{Co}}_{2}\mathrm{FeSi}$. This, combined with the large moment, cubic structure, and high Curie temperature supports the further investigation of ${\mathrm{Co}}_{2}\mathrm{FeSi}$ for spintronic applications that make use of the transport spin polarization.

Structural, Electronic, Mechanical and Thermodynamic Properties of Half-Metallic Rh <sub>2</sub>FeZ (Z = Ga, In) Full Heusler Compounds from First Principles

We report on the structural, electronic, mechanical, and thermodynamic properties of Rh2FeGa and Rh2FeIn full Heusler alloys from first principles. Results for the structural analysis establishes structural stability with a negative formation energy of -0.2175 eV and -0.2082 eV for Rh2FeGa and Rh2FeIn, respectively. The lattice constants and electronic properties compare favorably with reports from existing literature. The compounds are both anisotropic and mechanically stable, having checked out with the Born and Huang criteria. Rh2FeIn alloy is more ductile, yet, harder, and stiffer compared to its Rh2FeGa counterpart. The Debye temperatures of 400.124 K and 267. 738 K recorded for Rh2FeGa and Rh2FeIn, respectively, is consistent with the expectation that the main group element's atomic size has an inverse relationship with the Debye temperature. Therefore, indium with the larger atomic size has a lesser Debye temperature. Both compounds obey the Dulong-Petit limit at temperatures between 400 K and 500 K. The specific heat capacity at constant volume Cυof 96.5 J mol -1K-1 and 98 J mol -1K-1 for Rh2FeIn and Rh2FeGa alloys suggests a measure of thermodynamic stability of the compounds at moderate temperatures.

First principles calculations for electronic, optical and magnetic properties of full heusler compounds

For the investigation of structural, electronic, optical and magnetic properties of Co2CrZ (Z= In, Sb, Sn) compounds, we have used two different methods. One is based on full potential linearized augmented plane wave (FP-LAPW) method as implemented in WIEN2k and second is pseudo potential method as implemented in Atomistic Tool Kit-Virtual NanoLab (ATK-VNL). These compounds show zero band gap in their majority-spin and minority-spin representing metallic behavior except the compound Co2CrSb, which is showing the band gap 0.54 eV in their minority-spin near the Fermi level and viewing 100% spin polarization; which is implemented in WIEN2k code. Further, the compound Co2CrSb has been found to be perfectly half-metallic ferromagnetic (HMF). However, above mentioned compounds shows zero band gap in ATK-VNL code. Calculations performed using WIEN2k code shows the magnetic moment of these compounds Co2CrZ (Z= In, Sb, Sn) 3.11, 5.00 and 4.00µB respectively. However, the respective magnetic moment of these compounds is found to be 3.14, 5.05 and 4.12µB in ATK-VNL code. Calculated magnetic moments have good agreement with the Slater-Pauling behavior. Optical properties play an important role to understand the nature of material for optical phenomenon and optoelectronics devices. Value of absorption coefficient and optical conductivity of Co2CrSb is greatest than other two compounds. From the absorption and reflection spectra relation, observations indicate that absorption and reflectivity are inversely proportional to each other.

Electronic, Optical, Elastic and Magnetic Properties of Co2VZ (Z= As, B, In, Sb) Full Heusler Compounds

Here in, we have investigated electronic, optical, elastic and magnetic properties of Co2VZ (Z= As, B, In, Sb) full Heusler compounds by using two different computational methods. One is full potential linearized augmented plane wave (FP-LAPW) method as implemented in WIEN2k and second one is pseudo potential method as implemented in Atomistic Tool Kit-Virtual NanoLab (ATK-VNL). All these compounds shows zero band gaps in majority spin channel in both computational codes and in minority-spin conduction band or valence band crosses the Fermi level. Magnetic moment calculated by these compounds Co2VZ (Z= As, B, In, Sb) are 3.64 and 3.76, 2.00 and 1.97, 1.99 and 1.99, 3.96 and 3.82µB in WIEN2k and ATK-VNL simulation codes respectively. Optical properties of these compounds such as reflectivity, refractive index, excitation coefficient, absorption coefficient, optical conductivity and electron energy loss have been analyzed. Absorption coefficient and electron energy-loss function values are increases as we increase the value of energy. Absorption and reflection are inversely proportional to each other at same instant of time. Pugh’s ratio B/G is greater than 1.75 for Co2VZ (Z= B, In, Sb) compounds showing ductile in nature, but B/G value for Co2VAs is less than 1.75, so this compound is brittle in nature . Values of Cauchy pressure (CP = C12 – C44) derived and these compounds Co2VZ (Z= As, B, In, Sb) shows metallic nature.

Half-metallicity in new Heusler alloys Mn2ScZ (Z = Si, Ge, Sn).

Study of half-metallicity has been performed in a new series of Mn2ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U). Volume optimization in magnetic and non-magnetic phases for both the Cu2MnAl and Hg2CuTi type structures was done to predict the stable ground state configuration. The stability was determined by calculating their formation energy as well as from elastic constants under ambient conditions. A half-metal is predicted for Mn2ScSi and Mn2ScGe with a narrow band gap in the minority spin whereas Mn2ScSn shows a metallic nature. The magnetic moments of Mn and Sc are coupled in opposite directions with different strengths indicating that the ferrimagnetic order and the total magnetic moment per formula unit for half-metals follows the Slater Pauling rule. And a strong effect was shown by the size of the Z element in the electronic and magnetic properties.

Electronic structure and thermoelectric properties of full Heusler compounds Ca2YZ (Y = Au, Hg; Z = As, Sb, Bi, Sn and Pb).

We investigate the transport properties of bulk Ca2YZ (Y = Au, Hg; Z = As, Sb, Bi, Sn and Pb) by a combination method of first-principles and Boltzmann transport theory. The focus of this article is the systematic study of the thermoelectric properties under the effect of a spin–orbit coupling. The highest dimensionless figure of merit (ZT) of Ca2AuAs at optimum carrier concentration are 1.23 at 700 K. Interestingly enough, for n-type Ca2HgPb, the maximum ZT are close to each other from 500 K to 900 K and these values are close to 1, which suggests that semimetallic material can also be used as an excellent candidate for thermoelectric materials. From another viewpoint, at room temperature, the maximum PF for Ca2YZ are greater than 3 mW m−1 K−2, which is very close to that of ∼3 mW m−1 K−2 for Bi2Te3 and ∼4 mW m−1 K−2 for Fe2VAl. However, the room temperature theoretical κl of Ca2YZ is only about 0.85–1.6 W m−1 K−1, which is comparing to 1.4 W m−1 K−1 for Bi2Te3 and remarkably lower than 28 W m−1 K−1 for Fe2VAl at same temperature. So Ca2YZ should be a new type of promising thermoelectric material at room temperature.