Investigation of the quaternary Fe2− xCoxMnSi (0 ≤x≤ 0.6) alloys by structural, magnetic, resistivity and spin polarization measurements (original) (raw)
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Complex magnetic behavior and high spin polarization in Fe3−xMnxSi alloys
Physical Review B, 2011
Fe3Si is a ferromagnetic material with possible applications in magnetic tunnel junctions. When doped with Mn, the material shows a complex magnetic behavior, as suggested by older experiments. We employed the Korringa-Kohn-Rostoker (KKR) Green function method within density-functional theory (DFT) in order to study the alloy Fe3−xMnxSi, with 0 ≤ x ≤ 1. Chemical disorder is described within the coherent potential approximation (CPA). In agreement with experiment, we find that the Mn atoms align ferromagnetically to the Fe atoms, and that the magnetization and Curie temperature drop with increasing Mn-concentration x. The calculated spin polarization P at the Fermi level varies strongly with x, from P = −0.3 at x = 0 (ordered Fe3Si) through P = 0 at x = 0.28, to P = +1 for x > 0.75; i.e., at high Mn concentrations the system is half-metallic. We discuss the origin of the trends of magnetic moments, exchange interactions, Curie temperature and the spin polarization.
Effect of partial Mn substitution for Fe in Fe3Si on the structural, magnetic, transport, and magnetotransport properties has been studied. Mn substitution is found to induce a re-entrant antiferromagnetic phase at low temperatures. The increase in the antiferromagnetic exchange causes a gradual decrease in the Curie temperature and the saturation magnetization. Temperature dependence of the electrical resistivity data shows that the high temperature resistivity is dominated by electron-phonon scattering, while below the re-entry temperature (TR), electronmagnon scattering is dominant. These results are in agreement with the reported spin polarization studies and indicate that the reentrant behavior is detrimental to half metallicity. Application of a field causes negative magnetoresistance (MR) above TR. However, at 5K, the magnetoresistance is found to be positive, with the magnitude increasing with x. For x>0.8, field induced irreversibility has been found in MR vs. field isotherms at 5 K, which indicates that the re-entrant phase has competing magnetic interactions. Canted magnetic structure known to exist in this system is assumed to be responsible for this anomalous behaviour.
Journal of Applied Physics, 2010
First principle calculations using supercell approach and coherent potential approximation ͑CPA͒ are performed to investigate the electronic and magnetic structures of Fe 3−x Mn x Si and Fe 3−y MnSi y alloys, where x , y = 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.5, 1.75, and 2.25. Using supercell calculations we obtained a metallic behavior for x = 0, 0.25, and 0.5 in Fe 3−x Mn x Si alloys with spin polarizations of 24%, 39%, and 93%, respectively. The behavior starts to be half-metallic at x = 0.75 with a small direct band gap that increases for higher concentrations of Mn. Among the half-metallic systems, only those of L2 1 structure at x = 1 and 2 possess indirect band gaps along ⌫-X symmetry line. The change of Si concentration in Fe 3−y MnSi y structures retrieve the metallic behavior for all concentrations except y = 1.25 that shows a half-metallic behavior with a direct band gap of 0.27 eV. We obtained a good agreement between supercell and CPA calculations for the values of the magnetic moment and the trends of the formation energies, which reveals the validity of the supercell approach in predicting the magnetic structure and the energetics of doped Heusler alloys.
Structural and magnetic properties of MnCo1−xFexSi alloys
Journal of Magnetism and Magnetic Materials, 2015
The crystal structures, martensitic structural transitions and magnetic properties of MnCo 1-x Fe x Si (0 ≤ x ≤ 0.50) alloys were studied by differential scanning calorimetry (DSC), x-ray powder diffraction (XRD) and magnetic measurements. In high-temperature paramagnetic state, the alloys undergo a martensitic structural transitions from the Ni 2 In-type hexagonal parent phase to the TiNiSi-type orthorhombic martensite. Both the martensitic transition temperature (T M) and Curie temperatures of martensite (C M) decrease with increasing Fe content. The introduced Fe atoms establish ferromagnetic (FM) coupling between Fe-Mn atoms and destroy the double spiral antiferromagnetic (AFM) coupling in MnCoSi compound, resulting in a magnetic change in the martensite phase from a spiral AFM state to a FM state. For the alloys with x = 0.10, 0.15 and 0.20, a metamagnetic transition was observed in between the two magnetic states. A magnetostructural phase diagram of MnCo 1-x Fe x Si (0 ≤ x ≤ 0.50) alloys was proposed.
The Magnetic Properties of Mn x Fe1−x NiSi (x=0,0.25,0.5,0.75,1) Alloys
Journal of Superconductivity and Novel Magnetism, 2012
The magnetic properties of Mn x Fe 1−x NiSi (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x = 0.75.
A study of Fe2+xMn1-xAlFe2+xMn1-xAl alloys: Structural and magnetic properties
Physica B-condensed Matter, 2007
The Fe 2þx Mn 1Àx Al alloys were studied experimentally to assess the effect of variations of composition around stoichiometric on the structural and magnetic properties of this system. The results indicate that the ordered L2 1 ðX 2 YZÞ structure of full Heusler alloys can be stabilized with small deviations of composition from the stoichiometric 2:1:1. The saturation magnetization is strongly composition dependent and decreases with the increase of the Mn concentration, in spite of the fact that the Mn atoms carry the largest moment in the ordered phase. The highest Curie temperature was observed for the Fe-richer alloy. Magnetic measurements suggest that atomic disorder and competition of the antiferromagnetic Fe-Mn and Mn-Mn interactions with the ferromagnetic Fe-Fe, Mn-Mn and Fe-Mn interactions lead to a frustrated couplings ending in a reentrant spin-glass behavior at low temperature. r
A study of Fe 2 + x Mn 1 - x Al alloys: Structural and magnetic properties
Physica B-condensed Matter, 2007
The Fe 2þx Mn 1Àx Al alloys were studied experimentally to assess the effect of variations of composition around stoichiometric on the structural and magnetic properties of this system. The results indicate that the ordered L2 1 ðX 2 YZÞ structure of full Heusler alloys can be stabilized with small deviations of composition from the stoichiometric 2:1:1. The saturation magnetization is strongly composition dependent and decreases with the increase of the Mn concentration, in spite of the fact that the Mn atoms carry the largest moment in the ordered phase. The highest Curie temperature was observed for the Fe-richer alloy. Magnetic measurements suggest that atomic disorder and competition of the antiferromagnetic Fe-Mn and Mn-Mn interactions with the ferromagnetic Fe-Fe, Mn-Mn and Fe-Mn interactions lead to a frustrated couplings ending in a reentrant spin-glass behavior at low temperature. r
Journal of Magnetism and Magnetic Materials, 2015
Both Fe and Co K-edge x-ray magnetic circular dichroism (XMCD) have been employed as element-specific probes of the magnetic moments in the composition series of the disordered ferromagnet Fe 1-x Co x Si (for x = 0.2, 0.3, 0.4, 0.5). A definitive single peaked XMCD profile occurs for all compositions at both Fe and Co K-edges. The Fe 4p orbital moment, deduced from the integral of the XMCD signal, has a steep dependence on x at low doping levels and evolves to a different (weaker) dependence at x ≥ 0.3, similar to the behavior of the magnetization in the Co composition range studied here. It is systematically higher, by at least a factor of two, than the corresponding Co orbital moment for most of the composition series. Fine structure beyond the K-edge absorption (limited range EXAFS) suggests that the local order (atomic environment) is very similar across the series, from the perspective of both the Fe and Co absorbing atom. The variation in the XMCD integral across the Co composition range has two regimes, that which occurs below x=0.3 and then evolves to different behavior at higher doping levels. This is more conspicuously present in the Fe contribution. This is rationalized as the evolution from a half-metallic ferromagnet at low Co doping to that of a strong ferromagnet at x > 0.3 and as such, spin polarization crossover occurs. The Fermi level is tuned from the majority spin band for x < 0.3 where a strongly polarized majority spin electron gas prevails, to a regime where minority spin carriers dominate at higher doping. The evolution of the Fe-derived spin polarized (3d) bands, indirectly probed here via the 4p states, is the primary determinant of the doping dependence of the magnetism in this alloy series.
Theoretical and experimental study of FeSi on magnetic and phase properties
Applied Physics A, 2020
In the present work, the structural, magnetic, and theoretical analysis of the Fe-Si alloy prepared by melting and heattreated was performed. The ordered FeSi simple cubic (sc) phase was obtained by melting and heat treatment processes as determined by X-ray diffraction. The presence of the superstructure peak in the (312) crystalline direction confirms the high structural order reached. Using Mössbauer spectrometry (MS), a paramagnetic behavior with quadrupole splitting of SQ = 0.53 ± 0.02 mm/s was obtained. Although MS indicates paramagnetic behavior, vibrating sample magnetometry (VSM) showed ferromagnetic behavior with a coercive field of 25 Oe, associated with a small amount of Fe3Si segregations detected by scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). Using density functional theory (DFT), the crystalline structures for the simple cubic (sc) Fe 50 Si 50 , face-centered cubic (fcc) Fe 3 Si, and body-centered cubic (bcc) Fe 3 Si crystalline structures were simulated. Electron total density values were calculated to perform energetic comparisons with magnetic behavior. The electronic structures and magnetic properties of the Fe-Si alloys in different stoichiometric configurations were calculated by CASTEP, which employed first principles DFT. The density of states (DOS) and band structures were calculated together with magnetic properties. The results showed that the high value of the polarization spin for the fcc and bcc structures is due to the contribution of the high amount of Fe atoms above the Si atoms, which is reflected in an increase in the magnetic moment and that their presence could explain the ferromagnetic behavior observed by VSM.