research papers
Prediction of fully compensated ferrimagnetic spingapless semiconducting FeMnGa/Al/In half Heusler alloys
^{a}School of Civil Engineering, Guangzhou University, Guangzhou 510006, People's Republic of China, and ^{b}Department of Physics, University of Science and Technology Beijing, Beijing 100083, People's Republic of China
^{*}Correspondence email: zhliu@ustb.edu.cn, zgwu@gzhu.edu.cn
Materials with full spin polarization that exhibit zero net magnetization attract great scientific interest because of their potential applications in spintronics. Here, the structural, magnetic and electronic properties of a C1_{b}ordered FeMnGa alloy are reported using firstprinciples calculations. The results indicate that the corresponding band structure exhibits a considerable gap in one of the spin channels and a zero gap in the other thus allowing for high mobility of fully spinpolarized carriers. The localized magnetic moments of Fe and Mn atoms have an antiparallel arrangement leading to fully compensated ferrimagnetism, which possesses broken magnetic inversion symmetry. Such magnetic systems do not produce dipole fields and are extremely stable against external magnetic fields. Therefore, this will improve the performance of spintronic devices. Using this principle, similar band dispersion and compensated magnetic moments were predicted in a C1_{b}ordered FeMnAl_{0.5}In_{0.5} Heusler alloy.
Keywords: FeMnGa; Heusler alloys; halfmetallic fully compensated ferrimagnets; spingapless semiconductors; FeMnbased; full spin polarization; magnetic inversion symmetry.
1. Introduction
Cubic Heusler alloys are a rich family of materials that were first discovered by Heusler in 1903 (Heusler, 1903). These alloys have attracted much attention because of their wide range of extraordinary multifunctional properties including halfmetallic ferromagnetism (de Groot et al., 1983), thermoelectric materials (Uher et al., 1999), magnetic shape memory effects (Webster et al., 1984; Liu et al., 2003; Zhu et al., 2009) and tunable topological insulators (Lin et al., 2010). Halfmetallic (HMFs), which exhibit a complete spin polarization at the (E_{F}), are a natural source of spinpolarized current and are thus considered useful for spintronic applications (de Groot et al., 1983; Wolf et al., 2001). A nominally infinite magnetoresistance can be achieved if the two magnetic layers of magnetic tunnel junctions (MTJs) are replaced by HMFs (de Groot et al., 1983; Katsnelson et al., 2008). For example, giant tunnel magnetoresistance ratios of up to 1995% were obtained for epitaxial Co_{2}MnSi/MgO/Co_{2}MnSi MTJs, where Co_{2}MnSi is an HMF (Liu et al., 2012). However, most of the have a major drawback: the intrinsic net dipolar moment hinders the performance of the nearby device arrays or the multilayer bits in spintronic chips (Hu, 2012). Materials with no net magnetization but high spin polarization are therefore in high demand (Hu, 2012). Obviously, this is impossible for conventional antiferromagnets (AFMs) because of the symmetry of spin rotation, which leads to no spin polarization (de Groot, 1991). Breaking the symmetry of spin rotation is then a requirement for spintronic materials in AFMs (Venkateswara et al., 2018). Halfmetallic antiferromagnets (HMAFMs), which show 100% spin polarization while having zero net magnetization, are one of the most promising candidates (van Leuken & de Groot, 1995; Akai & Ogura, 2006). HMAFMs were thought to be a special case of ferrimagnets because of the fact that they have no inversion symmetry in magnetic structure (Wurmehl et al., 2006). Because of this they were later renamed halfmetallic fully compensated ferrimagnets (HMFCFs) (Wurmehl et al., 2006).
In L2_{1} ordered X_{2}YZ Heusler alloys, when X and Y atoms carry a moment and the X–Y coupling is antiparallel, the alloys are ferrimagnets. In a carefully selected material the total (M) can be zero (Galanakis et al., 2007). This is based on the famous Slater–Pauling rule, which for X_{2}YZ Heusler alloys is M = N_{v} − 24, where N_{v} is the number of valence electrons per formula (Galanakis et al., 2002b). The ordered L2_{1} structure has four formula units per cubic with X in A (0, 0, 0) and C (0.5, 0.5, 0.5) sites, Y in B (0.25, 0.25, 0.25) sites and Z in D (0.75, 0.75, 0.75) sites of the Wyckoff coordinates (Cu_{2}MnAltype structure). When the valence of Y is larger than that of X, the atomic sequence is then X–X–Y–Z and the prototype is Hg_{2}TiCu, which is known as an inverse Heusler alloy (Özdoğan & Galanakis, 2009). A well known example is Mn_{2}CoAl (M = 2 μ_{B}) (Liu et al., 2008). There are three different variants, i.e. M = N_{v} − 18, M = N_{v} − 24 and M = N_{v} − 28, of the Slater–Pauling rule for the inverse Heusler alloys depending on the chemical type of the constituent transitionmetal atoms (Skaftouros et al., 2013a). For C1_{b}ordered XYZ half Heusler alloys, the form of the Slater–Pauling rule is then M = N_{v} − 18. The original example of an HMF was NiMnSb (M = 4 μ_{B}) (de Groot et al., 1983). Quaternary Heusler alloys XX′YZ also obey the Slater–Pauling rule (Özdoğan et al., 2013). Therefore, a generalized version of the Slater–Pauling rule can be extracted for the Heusler alloys, and halfmetallic Heusler alloys with N_{v} = 18, 24 or 28 should be the likeliest candidates for HMFCFs (Wurmehl et al., 2006).
It should be noted that in all HMFCFs, transport is mediated by electrons having only one kind of spin, since the band structure is metallic in one spin channel. In a recently proposed new class of materials named spingapless semiconductors (SGSs), the realization of band gaps in both spin directions, i.e. an open band gap in one spin channel and a closed gap in the other, seems possible (Wang, 2008; Ouardi et al., 2013). An SGS has 100% spinpolarized carriers with tunable capabilities and the speed of the fully polarized spin electrons in the SGS could be much faster than in diluted magnetic semiconductors (Wang et al., 2009). As shown in Fig. 1, the SGS band structure and zero net are realized in the same material suggesting the discovery of a novel class of materials with both the features of HMFCFs and SGSs. These were named fully compensated ferrimagnetic spingapless semiconductors (FCFSGSs) (Jia et al., 2014; Zhang et al., 2015b). Because of their unique properties, full spin polarization, higher mobility of carriers and absence of stray fields generation are expected, thus leading to minimal energy losses using FCFSGSs as electrode materials in spintronics devices (Han & Gao, 2018; Baltz et al., 2018).
To date, FCFSGSlike properties have been observed in several Heusler ferrimagnets (Jia et al., 2014), including Ti_{2} and Cr_{2}based inverse Heusler (Skaftouros et al., 2013b), Mnbased half Heusler (Zhang et al., 2015b), and quaternary Heusler CrVTiAl (Venkateswara et al., 2018). So far few of them have been experimentally realized because generally they turned out to be unstable, or crystallized with a different structure (Feng et al., 2015; Venkateswara et al., 2018). The growth of the Heusler ferrimagnet Ti_{2}MnAl on an Si (001) substrate has been attempted using magnetron sputtering but the samples obtained were of poor crystallinity (Feng et al., 2015). The higher energy configuration CrVTiAl has a spingapless semiconducting nature but the corresponding configuration is not a ground state (Venkateswara et al., 2018). We recently found several new FCFSGS candidates based on the Slater–Pauling rule (Zhang et al., 2015b). But these candidates are not easy to realize in experiments. For example, C1_{b}type Mn_{2}Si was predicted to be an FCFSGS. However, Mn_{2}Si alloy actually crystallized with a different structure. Therefore, the search for FCFSGSs with a high possibility of experimental realization is still under the spotlight in spintronics.
In this study, we report that an equiatomic FeMnGa alloy with C1_{b}ordered structure can show both zero net moment and SGS properties at the same time and have a fair chance of realization. FeMnGa alloys were originally proposed as magnetic shape memory materials (Zhu et al., 2009; Omori et al., 2009; Liu et al., 2018). Stoichiometric Fe_{2}MnGa has an L2_{1}ordered full Heusler structure (Xin et al., 2016). Although the of stoichiometric FeMnGa has not been confirmed experimentally yet, the C1_{b}ordered structure is likely to be realized in this alloy because of two considerations. First, FeMnGa alloys crystallize to an L2_{1}ordered cubic phase in quite a large composition range (Omori et al., 2009). Second, stoichiometric Ni_{2}MnGa (Webster et al., 1984) and Co_{2}MnGa (Hames, 1960) are L2_{1}ordered full Heusler alloys, and their equiatomic forms of NiMnGa (Ding et al., 2017) and CoMnGa (Wang et al., 2014) were all confirmed to be C1_{b}ordered structures by experiment. In addition, competing magnetic behaviour was recently observed in Fe_{41}Mn_{28}Ga_{31} (Sun et al., 2018). Therefore, experimental realization of C1_{b}ordered FeMnGa with zero net magnetization seems feasible. In the present work, we performed a detailed firstprinciples calculations study on the structural, electronic and magnetic properties of a C1_{b}ordered stoichiometric FeMnGa alloy. The results show that C1_{b}ordered FeMnGa is a potential FCFSGS. Similar band dispersions and magnetic properties were also found in FeMnAl_{0.5}In_{0.5} by firstprinciples calculations. Details are provided in the following sections.
2. Computation details and methods
Calculations were performed using the Vienna ab initio simulation package (VASP) (Hafner, 2008). The electronic exchange and correlation used a spinpolarized generalizedgradient approximation (GGA) of density functional theory (DFT) and the electron–ion interaction was described within the framework of projector augmentedwave formalism. The wave cutoff was set to 500 eV and a 15 × 15 × 15 mesh for the reciprocalspace integration with a Monkhorst–Pack scheme was used for good convergence.
According to the literature, the influence of d series elements (Mavropoulos et al., 2004). Therefore, SOC of the alloys was not employed in the calculations. For magnetism, the orbital moments originated from SOC are expected to be very small in FeMnbased alloys (Galanakis, 2005), thus the spin and orbital moments were not separated here.
(SOC) on the band gap of Heusler alloys is insignificant for the 3The SGS properties were further confirmed by the selfconsistent fullpotential linearized augmented planewave method (Wimmer et al., 1981; Weinert et al., 1982). It should be pointed out that the modified Beche–Johnson (MBJ) exchange potential + local density approximation (LDA) correlation, which allows the calculation of band gaps with an accuracy similar to GW calculations, was also employed. The electronic and magnetic properties of disordered systems were calculated using the Korringa–Kohn–Rostoker (KKR) Green's function method combined with the coherent potential approximation (CPA) (Katayama et al., 1979; Blügel et al., 1987; Kaprzyk & Bansil, 1990). This is a powerful method for disordered systems.
3. Results and discussion
3.1. and compensated ferrimagnetism
Half Heusler alloys with a general formula XYZ, where X and Y are transition metals, and Z is a main group element, crystallize in a noncentrosymmetric C1_{b} structure. The most well known one is NiMnSb, which was found to be an HMF by de Groot et al. (1983). It is a ternary ordered variant of the CaF_{2} structure and can be derived from the tetrahedral ZnStype structure by filling the octahedral lattice sites. The C1_{b}type FeMnGa alloy considered here consists of three interpenetrating f.c.c. sublattices, each of which are occupied by Fe, Mn and Ga atoms. Fig. 2 and Table 1 show the three possible inequivalent atomic arrangements and the corresponding occupied Wyckoff positions by fixing Ga at the D site.

We first performed structural optimization calculations to determine the lattice parameters and the ground state of C1_{b}ordered FeMnGa. Three possible arrangements of atoms are summarized in Table 1 and three kinds of magnetic orders, i.e. paramagnetic, ferromagnetic and antiferromagnetic states, are considered in the calculations. The paramagnetic (or nonmagnetic) state means that the constituent atoms of FeMnGa have no spin polarization. The ferromagnetic (or antiferromagnetic) state means the parallel (or antiparallel) alignment of the magnetic moments of the Fe and Mn atoms. Although the more precise term to describe them was thought to be compensated ferrimagnets as used in the literature (Galanakis et al., 2014), the term we use here is still AFMs, which is a more general term. The moments of the Z atoms are usually ignored since most of them are close to zero.
Fig. 3(a) shows the calculated total energy as functions of lattice constant for FeMnGa. It can be seen that a ferromagnetic state of Type I or II configuration appears only when the lattice constants of the crystal go beyond 5.8–6.0 Å, because the ferromagneric state of FeMn cannot be stabilized in a selfconsistent process below a critical distance between Fe and Mn atoms. This can be explained by the Bethe–Slater curve which shows that MnMn or MnFe atoms tend to couple antiferromagnetically when they are first nearest neighbours or the distance between them is less than a certain value (Khovaylo et al., 2009). Similar situations also occur in many other Heusler alloys, such as NiMnGa, Fe_{2}MnGa, Mn_{2}FeGa, MnCrZ (Z = Al, Si and Sb) and FeCrZ (Z = Ga, Ge and As) (Fujii et al., 2010; Zhang et al., 2018). For Type III configuration [Fig. 2(c)], Fe and Mn atoms have a larger distance which results in a possible ferromagnetic coupling. Among all these calculated states, the Type I antiferromagnetic state is the most stable one since it has the lowest energy. This structure type agrees with the already observed half Heusler alloys (de Groot et al., 1983; Galanakis et al., 2002a). The optimized equilibrium lattice constant is a = 5.50 Å.
Fig. 3(b) shows the atomic resolved and total magnetic moments of the as a function of the lattice constants. For the equilibrium lattice constant, the calculation reveals nearly full compensation of the magnetic moments. A change in the lattice parameter by up to −1.8 to 3.6% (5.4–5.7 Å) with respect to the equilibrium one only alters the local magnetic moments of the Mn and Fe atoms. An overall increase in the lattice parameter slightly increases the of the Mn atoms and decreases the of the Fe atoms. The total of zero, as a sum of those of each atom, remains unaffected. This result indicates the fully compensated ferrimagnetism and the halfmetallic character of FeMnGa. The of the halfmetallic C1_{b} Heusler alloys follows the simple rule: M = N_{v} − 18. The robustness of the fully compensated ferrimagnetism originates from the large halfmetallic gap of the minority channel that is induced by the of transitionmetal atoms, as observed in many other Heusler type compounds (Galanakis et al., 2002b). The and details of the electronic structure of FeMnGa were analysed and are discussed below.
3.2. Electronic structure of FeMnGa
Detailed analyses of atomic et al. They found that, for most of the Heusler alloys, the band gap mainly arises from the of d states of the transitionmetal atoms (Galanakis et al., 2002a,b). The possible orbitals for C1_{b} FeMnGa from low energy to high energy according to the literature are 1 × s, 3 × p, 2 × e_{g}, 3 × t_{2g}_{,}, 2 × e_{g} and 3 × t_{2g} as shown in Fig. 4(a) (Galanakis et al., 2002a).
and the origin of the halfmetallic band gap in studies of Heuslerbased HMFs have been performed by GalanakisFigs. 4(b)–4(d) display the spinresolved band structure and (DOS) of FeMnGa at the equilibrium lattice constant. The relative band structure shows that the spindown state has a real gap between the [t_{2g}]Γ point and the [e_{g}]Γ point with the maximum (VBM) at the Γ point and the minimum (CBM) at the X point. Hence the gap of the spindown state is an indirect one, which agrees with many of the C1_{b}type Heusler compounds (Zhang et al., 2015a,b). There is also a considerable gap between the [t_{2g}]Γ point and the [e_{g}]Γ point in the spinup channel, but the VBM and CBM are not located at the Γ point. Instead, they are located at the L and X points, respectively. In addition, the and overlap at the X point resulting in a pseudogap at the The obtained spindown DOS clearly shows a gap at the (E_{F}), while the spinup DOS exhibits a valley shape with the minimum value being close to zero and located at E_{F}. This shape follows the idealized DOS for SGS (Wang, 2008). Similar electronic structure was observed in many other Heusler alloys, such as Mn_{2}CoAl (Ouardi et al., 2013). However, most of them have a considerable FeMnGa is a very special case in which the total spin moment is exactly 0 μ_{B}. Compared with the widely studied SGS material Mn_{2}CoAl, whose magnetization is 2 μ_{B}, FeMnGa will offer a superior advantage owing to its ideally compensated magnetic moment.
Note that the closed gap of the spindown channel is not a real zero width gap. The et al., 2017). Fig. 5(a) shows the DOS of FeMnGa for different lattice constants. Either expansion or contraction of the lattice results in a practically rigid shift of the bands with small rearrangements of the shape of the peaks to account for the charge neutrality (Galanakis et al., 2002a). It is clearly seen that expansion by less than 1% (5.55 Å) opens a real narrow gap in the spinup channel. Fig. 5(b) shows the corresponding band structure. It can be seen that both the VBM ([t_{2g}]L point) and the CBM ([e_{g}]X point) in the spinup channel touch the and form a zero width gap, while the VBM and CBM of the spindown channel form an open gap with a width of ∼0.5 eV. This clearly follows the idealized band structure for SGSs.
cuts a little of the Uniform strain, simulated by changing the lattice constants, has often been used to open a real band gap in many Heusler alloys (WangIt should be pointed out that the band structures based on the LDA + MBJ [see Fig. 5(b) red solid line] are similar to those based on the GGA [see Fig. 5(b) blue dashed line] and show SGS properties. As summarized in Table 2, contraction results in a small net because of the destroyed spindown gap, while expansion retains the zero net This indicates that FeMnGa has the potential for the realization of FCFSGS.

From the discussion above, we can see that the fully compensated ferrimagnets with spingapless semiconducting nature can arise with net spin N_{s} = 0 as the number of up and down electrons are equal. Such materials have the advantage of being able to generate fully spinpolarized current while exhibiting zero net magnetization. This is very different from a conventional AFM, in which the vanishing of the net originates from a symmetry relation between sites of opposite spin. It causes the electronic structure of the two spin directions to be identical, which results in no polarization of the conduction electrons (de Groot, 1991). In the magnetic structure of FeMnGa, as shown in Table 2, the cancellation of the is not caused by a symmetry relation between sites with up and down spins, instead the moments of Fe are cancelled by the moments of Mn at different crystallographic sites. It can be seen that the magnetic moments of Fe atoms are not equal to those of Mn atoms. Ga atoms also carry a small spin indicating the breaking of magnetic inversion symmetry. This is one of the features of fully compensated ferrimagnetism (Venkateswara et al., 2018).
Another important feature of FeMnGa that differs from conventional AFMs is that the electronic structures for the two spin directions are completely asymmetrical with respect to the spin direction, as shown in the DOS of Fig. 4(c). This is because the distributions of electronic states of Fe and Mn atoms in FeMnGa as a function of energy are totally different from each other. Fig. 6 shows the atomresolved DOS, which demonstrates that the local DOS of Fe and Mn have a totally different distribution and do not completely compensate each other resulting in a spin polarization.
From the atomresolved DOS of FeMnGa as shown in Fig. 6, it can be seen that the contribution of Ga is not dominant in forming the total DOS of the alloy. However, Ga plays a very important role in forming the SGS property in FeMnGa, as observed in many other alloys (Galanakis et al., 2002a). This is because the Ga atom has three valence electrons, and in FeMnGa each Ga atom introduces a deep lying s band, and three p bands below the centre of the d bands. These bands accommodate a total of eight electrons per so that formally Ga acts as a fivecharged Ga^{5−} ion. Analogously, an Sb atom behaves in NiMnSb as an Sb^{3−} ion. This does not mean that locally such a large charge transfer exists. In fact, the s and p states strongly hybridize with the transitionmetal d states, and the charge in these bands is delocalized and locally Ga loses only about one electron, if one counts the charge in the Wigner–Seitz cells. What does count is that the s and p bands accommodate eight electrons per thus effectively reducing the d charge of the transitionmetal atoms. This will have a crucial effect on the distribution of the density state of each magnetic atom, hence affecting the total DOS of the alloy.
Fig. 7 shows the atomresolved DOS of Fe, Mn and Ga atoms for C1_{b} FeMnGa (blue curve) and for FeMn (red curve) with the Ga atom removed from the crystal. Since the Ga atom is removed from the crystal, Fig. 7(c) only gives the DOS of Ga for C1_{b} FeMnGa. In the FeMn crystal hypothetical alloy (red curve), there is a gap in the spindown channel for DOS of both Fe and Mn, and E_{F} is located at the gap in the spindown bands and crosses a peak in the spinup bands. As Ga atoms are added to the structure, the DOS of Fe and Mn have a totally different distribution which shows a large overlap in energy with the DOS of Ga atoms. This indicates a strong between the d states of the transition metals Fe and Mn, and the p states of the main group element Ga. The interaction of FeMnd and Gap leads to the redistribution of electrons in the FeMn alloy, hence producing the spingapless semiconducting property in C1_{b}ordered FeMnGa alloy.
The C1_{b} structure has high atomic order, while atomic disorder is sometimes inevitable in Heusler alloys. Such structural details were treated by applying the CPA. Three atomic disorders, i.e. Fe–Ga, Mn–Ga and Fe–Mn were considered in the present work. The results are given in Fig. 8. It can be seen that the DOS exhibits SGS properties when x = 0. With the increase in the degree of disorder of Fe–Ga, Fe–Mn or Mn–Ga, the SGS properties gradually disappear. The SGS properties were totally destroyed when x = 0.5, especially for MnGa and FeGa disorder. This indicates that the distribution of DOS is very sensitive to atomic disorder, which reduces between the d states of the transitionmetal atoms resulting in smaller exchange splitting of the d band (Özdoğan & Galanakis, 2011). It should be noted that the DOS of ordered FeMnGa (x = 0) based on the KKRCPA has a smaller energy gap with respect to the results based on the DFTGGA (as shown in Fig. 6). Similar cases also exist in the well known SGS Mn_{2}CoAl (Liu et al., 2008; Xu et al., 2014). The important conclusion, however, is that the atomic disorder has a crucial influence on electronic structure. Therefore, highly ordered C1_{b} structure is important for obtaining SGS properties.
FeMnGa alloys can crystallize in different structural phases when treated under different conditions. The B2 phase can be obtained with annealing at 1073–1373 K (Zhu et al., 2009; Yang et al., 2016). The highly ordered C1_{b} (or L2_{1}) phase is usually obtained from the B2 phase by ordering treatment (Ishikawa et al., 2008). An Ni_{3}In type hexagonal phase was recently observed with annealing at 873–923 K (Okumura et al., 2014; Liu et al., 2018). The order–disorder transition temperature from the B2 to C1_{b} (or L2_{1}) phase in Heusler alloys is always between 773 and 973 K (Ishikawa et al., 2008). Therefore, it is necessary to carefully avoid the hexagonal phase when obtaining the C1_{b} phase in experiment.
3.3. Isoelectronic substitution
Since FeMnZ (Z = Al, In) have the same valence electrons as FeMnGa, they meet the requirement of fully compensated ferrimagnetism according to the Slater–Pauling rule. Therefore, we also performed calculations on these alloys. The optimized equilibrium lattice constants for FeMnAl and FeMnIn are 5.44 and 5.98 Å, respectively. Table 2 gathers their corresponding atomic and total spin magnetic moments. The moments of the Al and In atoms are negligible. The Fe and Mn atoms contribute the main local magnetic moments and are arranged antiparallel to each other. This leads to a small nonzero net spin deviating from the Slater–Pauling rule, which indicates the loss of SGS properties. The corresponding band structures for FeMnAl and FeMnIn are present in Fig. 9. The band structures represented in Figs. 9(a) and 9(c) are with equilibrium lattice constants. No SGS properties are observed. Both the and band structures indicate that FeMnAl and FeMnIn in the ground state are not FCFSGSs. However, by correcting the lattice constants of FeMnAl and FeMnIn, the would again move into the gap. As shown in Figs. 9(b) and 9(d), expansion and contraction of the lattice constants can induce SGS electronic structures in FeMnAl and FeMnIn, respectively, and we can see that both FeMnAl and FeMnIn present FCFSGS for the specific lattice constant of 5.70 Å. This means that the lattice constant of 5.70 Å is a key point for realising FCFSGS. The problem is that expansion of 4.78% for FeMnAl and contraction of 4.68% for FeMnIn are too large to realize in practice. A more feasible way to modulate the lattice constant experimentally is to isoelectronically replace the sp element with an element in the same main group. This will effectively change the lattice constant because of the different atomic radii, thereby adjusting the energy gap without altering the number of valence electrons. Based on the calculations, we found that the optimized equilibrium lattice constant of FeMnAl_{0.5}In_{0.5} is exactly 5.70 Å, and the band structure exhibits the idealized SGS behaviour as shown in Fig. 9(e), the of which is 0 μ_{B} as shown in Table 2. Therefore, substituting 0.5In for Al may realize FCFSGS properties in its ground state in FeMnAl (In).
4. Conclusions
In this work, we employed firstprinciples calculations to investigate the C1_{b}ordered stoichiometric half Heusler FeMnAl/Ga/In alloys. Our calculations show that the band structure of FeMnGa exhibits a considerable gap in one of the spin channels and a zero gap in the other thus allowing for higher mobility of fully spinpolarized carriers. The band gap originates from the strong between the d states of the transitionmetal atoms. The interaction of FeMnd and Gap leads to the redistribution of the electronic states of the Fe and Mn atoms, which is very important for the formation of SGS properties. The localized magnetic moments of the Fe and Mn atoms have an antiparallel arrangement leading to a fully compensated ferrimagnetism. The exact cancellation of the originates from the antiparallel arrangement of inequivalent magnetic ions (Fe and Mn) being totally different from that of conventional antiferromagnets. One of the most important features is that the electronic structure for the two spin directions is completely asymmetrical with respect to the spin direction, which comes from the asymmetrical distributions of the electronic states of the Fe and Mn atoms. These results indicate that the C1_{b}ordered stoichiometric FeMnGa is an HMFCF with a spingapless semiconducting nature. The highly ordered C1_{b} structure is very necessary because the SGS properties are very sensitive to atomic disorder. Similar band dispersion and compensated moments were found in C1_{b}ordered half Heusler FeMnAl_{0.5}In_{0.5} alloys. This work is expected to enrich the diversity of spinpolarized antiferromagnetic materials and boost the development of spintronics.
electronic and magnetic properties ofFunding information
The following funding is acknowledged: the National Natural Science Foundation of Guangdong Province (grant No. 2018A 030313742) and the National Natural Science Foundation of China (grant No. 51671024).
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