Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl

Abstract

Half-metallic ferromagnets (HMF) are on one of the most promising materials in the field of spintronics due to their unique band structure consisting of one spin sub-band having metallic characteristics along with another sub-band with semiconductor-like behavior. In this work, we report the synthesis of a novel quaternary Heusler alloy FeMnVAl and have studied the structural, magnetic, transport, and electronic properties complemented with first-principles calculations. Among different possible structurally ordered arrangements, the optimal structure is identified by theoretical energy minimization. The corresponding spin-polarized band structure calculations indicates the presence of a half-metallic ferromagnetic ground state. A detailed and careful investigation of the x-ray diffraction data, Mössbauer and nuclear magnetic resonance spectra suggest the presence of site-disorder between the Fe and Mn atoms in the stable ordered structure of the system. The magnetic susceptibility measurement clearly establishes a ferromagnetic-like transition below ∼213 K. The 57 Fe Mössbauer spectrometry measurements suggest only the Mn-spins could be responsible for the magnetic order, which is consistent with our theoretical calculation. Surprisingly, the density-functional-theory calculations reveal that the spin-polarization value is almost immunized (92.4% → 90.4%) from the Mn-Fe structural disorder, even when nonmagnetic Fe and moment carrying Mn sites are entangled inseparably. Robustness of spin polarization and half metallicity in the studied FeMnVAl compound comprising structural disorder is thus quite interesting and could provide a new direction to investigate and understand the exact role of disorders on spin polarization in these class of materials, over the available knowledge.

High spin-polarization in a disordered novel quaternary Heusler alloy FeMnVGa

“…Such robustness of HMF behaviour despite having a large crystal disorder are rarely displayed by the Heusler alloy group of material and is quite unique over other reported HMF materials in Heusler alloys. Incidentally, such coexistence of high spin-polarization along with structural disorder have earlier been reported in a related system, FeMnVAl [56]. In both the cases, structural disorder enhances the symmetry of the crystal structure maintaining it's prime feature (half-metallcity) near the Fermi level.…”

CoMnCrGa: a novel ferromagnetic material with high spin-polarization for room temperature spintronics

“…Standard EXAFS measurement protocols have been used as detailed elsewhere. 20,31 High-temperature VSM (Model EV9, MicroSense, LLC Corp., USA) was used to measure the magnetization (M) vs. temperature (T) in the range of 300-900 K. M vs. field (H) measurement was carried out using a superconducting quantum interference vibrating sample magnometer (Quantum design Inc.,USA) in the magnetic fields up to AE70 kOe at 5 K. Four-probe resistivity measurement in the absence of a magnetic field was carried out in a Physical Property Measurement System (Quantum Design Inc., USA).…”

“…[14][15][16][17] As a result of this substitution, the crystal structure transforms to a lower symmetry space-group, where the 8c site in the Fm% 3m space group splits into 4c and 4d sites in the F% 43m space group. Recently, quaternary Heusler alloys attracted a lot of attention from the research community due to their HMF, [18][19][20][21][22] spingapless semiconductors, [23][24][25][26][27][28] spin-semimetal, 29 spin glass, 30 re-entrant spin glass 31 and bipolar magnetic semiconducting properties. 32 However, the structural disorder, which is quite inherent for Heusler alloys, is known to have a significant impact on the magnetic as well as the electronic structure.…”

“…The electronic structure of a material is altered by disorder, which changes the density of states, generates local magnetic moments, and narrows the band gap in the half-metallic ferromagnetic materials. These changes result in a reduced a Condensed Matter Physics Division, Saha Institute of Nuclear Physics, A CI of magnetic moment, lower magnetic ordering temperature, 31,33 weakened magnetic anisotropy, and decreased electrical conductivity. It makes sense that in order to preserve the halfmetallic ferromagnetic properties, either the compound must be synthesized without defects or one must find compounds where the properties are resilient to disorder.…”

Rare observation of spin-gapless semiconducting characteristics and related band topology of quaternary Heusler alloy CoFeMnSn

“…Subsequently, two major types of Heusler alloys are considered: i) full Heusler alloy represented stoichiometrically by the formula X 2 YZ ii) half Heusler alloy represented as XYZ, where X and Y are transition elements and Z is a sp-group element [10,11]. Recently, another new variant quaternary Heusler represented by XX Y Z has been introduced [8,[12][13][14][15]. As most of the practical usages of spintronics require room temperature applications, Co-based full/quaternary Heusler alloys have attracted a lot of attention due to their high Curie temperature (T C ) and tunable electronic structure [11,14,[16][17][18].…”