Magnetic Moments Of Mn Atoms Research Articles

Mössbauer Study of Cubic Phase in the Mn-Sb System

One of the methods to produce novel materials is high temperature and high pressure treatment. In such a manner in the Mn Sb system the cubic modi cation of Mn3Sb could be produced [1, 2]. This compound has the L12-type of crystal structure (Cu3Au) with the lattice parameter a = 0.400 nm. The Mn atoms occupy 3c positions with the coordinates (0, 1/2, 1/2), the Sb atoms the positions 1a (0, 0, 0), Fig. 1. In normal conditions, the compound exists in a thermodynamically non-equilibrium state and decomposes at 420 K on the Mn2Sb + Mn phases. The magnetic measurements of the Mn3Sb were performed by the Faraday method in the eld 8.6 kOe and the temperature region from the liquid nitrogen to the temperature of phase decomposition. The derived value of speci c magnetization is very small, ≈ 1.0 A m/kg [2]. The neutron di raction analysis for the Mn3Sb was performed as well [3]. The data obtained were interpreted in the model of the ferrimagnetic ordering of Mn magnetic moments. The magnetic moments of Mn atoms are supposed to be antiparallel and have di erent values initially taking into account the similar local environment of Mn atoms in both tetragonal Mn2Sb and cubic Mn3Sb. However, it is possible to interpret the neutron di raction data in a di erent way, using the model of triangular magnetic ordering of Mn magnetic moments. In contrast to previous one, in this model the Mn atoms are considered to have equal magnetic moments ordered in the (111) plane and forming an equilateral triangle with each moment pointing to the center of the triangle. The similar model was used in [4] to describe the magnetic ordering of Mn in Mn3Pt with the same L12 type of structure below 400 K. Thus the model of the magnetic ordering of Mn atoms in the cubic Mn3Sb is ambiguous. Therefore the purpose of this study was to get Mossbauer information on the number of magnetically nonequivalent states of Mn atoms and to clarify a type of the magnetic ordering in Mn3Sb.

Reentrant quantum anomalous Hall effect with in-plane magnetic fields in HgMnTe quantum wells

Quantum anomalous Hall effect has been predicted in HgMnTe quantum wells with an out-of-plane magnetization of Mn atoms. However, since HgMnTe quantum wells are paramagnetic, an out-of-plane magnetic field is required to polarize magnetic moments of Mn atoms, which inevitably induces Landau levels and makes it difficult to identify the origin of the quantized Hall conductance experimentally. In this work, we study the quantum anomalous Hall effect in the presence of an in-plane magnetic field in Mn doped HgTe quantum wells. For a small out-of-plane magnetic field, the in-plane magnetic field can drive the system from a normal insulating state to a quantum anomalous Hall state. When the out-of-plane magnetic field is slightly above the transition point, the system shows a reentrant behavior of Hall conductance, varying from $-e^2/h$ to 0 and back to $-e^2/h$, with increasing in-plane magnetic fields. The reentrant quantum anomalous Hall effect originates from the interplay between the exchange coupling of magnetic moments and the direct Zeeman coupling of magnetic fields. The calculation incorporating Landau levels shows that there is no qualitative change of the reentrant behavior.

Half-metallicity of the inverse Heusler alloy Mn2CoAl(0 0 1) surface: A first-principles study

Half-metals exhibit 100% spin polarization at the Fermi level. Thus, they are promising magnetic electrode candidates in spintronics. We investigated the electronic structures, magnetism, and half-metallicity of the inverse Heusler alloy Mn2CoAl(001) surface by the all-electron full-potential linearized augmented plane-wave method within the generalized gradient approximation. Two types of surface terminations were considered, namely, the AlMn terminated (AlMn-term) and CoMn terminated (CoMn-term) surfaces. From the calculated layer-projected density of states, we found that the half-metallicity was preserved on the surface of the AlMn-term. However, the width of the minority-spin gap was significantly reduced because of the surface states located just above the Fermi level. By contrast, the CoMn-term lost its half-metallicity because of the strong surface potential effect on the surface Co atom. The magnetic moments of Mn atoms on the surfaces of both terminations are considerably increased compared with those in the deep inner layers, while that of the surface Co atom on the CoMn-term is slightly increased.

ChemInform Abstract: Ni—Mn—X Heusler Materials

AbstractReview: X: Al, Ga, In; 45 refs.

Direction and Size of Ir Magnetic Moment Induced in MnIr/Co1-xFexExchange Bias Bilayers from Resonant X-ray Magnetic Scattering Experiments at the Ir L3Absorption Edge

Interface magnetism was investigated for Ir atoms in Mn73Ir27/Co70Fe30 and Mn77Ir23/Fe bilayers which showed an exchange bias effect. Scattering angle and X-ray energy dependent resonant X-ray magnetic scattering patterns were measured at a small angle region around the Ir L3 absorption edge to determine the induced magnetic structure of the Ir 5d magnetic moment. It is found that the induced Ir magnetic moment which follows applied field reversal is concentrated at the first atomic layer of the antiferromagnetic MnIr layer for both MnIr/CoFe and MnIr/Fe samples. The direction of the Ir moment is parallel to the magnetic moment of the ferromagnetic layer independent of the composition of the ferromagnetic layer. This behavior is different from that reported on the uncompensated 3d magnetic moment of Mn atoms. The average size of the Ir moment in the MnIr/CoFe bilayer is estimated to be about 1.4 times larger than that in the MnIr/Fe bilayer. These results are consistent with a first-principles band calcul...

Temperature dependences of structure and coercivity for melt-spun MnBi compound

Low temperature phase MnBi compound was prepared by annealing the melt-spun amorphous MnBi ribbons. Temperature dependences of structure, magnetization and coercivity were investigated using neutron/X-ray powder diffraction and magnetic measurements. It is found that the lattice parameter c/a ratio of the MnBi increases with the increasing temperature and finally reaches a maximum of 1.433 around 600K. No structural phase transition is observed at 633K. Especially, the lattice constants of MnBi at 700K are a=b=4.30919Å, and c=6.17521Å, which are not in accordance with the previous data for bulk MnBi. Magnetic moment of Mn atom tends to lie in the ab-plane at 10K, and turns to align along c-axis around 90K. The growth of LTP MnBi grains is observed above 500K, which increases the content of MnBi. The coercivity of MnBi shows a positive temperature coefficient, reaches a maximum of 2.5T at 540K, and decreases to 1.8T at 610K. The temperature dependence of the coercivity is related to the change of magnetocrystalline anisotropy, and shows strong dependence on the sizes of MnBi particles.

Symmetry analysis of the magnetic structure of Mn3Sb

To estimate the reliability of the previously published results concerning the magnetic structure of Mn3Sb, a symmetry analysis of possible magnetic structures characterized by a wave vector k 12 = 0 has been performed. In this work, we quite briefly describe and apply the previously developed technique for the calculations of the basis functions of the irreducible representations of the space group O h 1 (Pm \(\bar 3\) m) entering into the composition of the magnetic representation with the above wave vector. Results of the calculations of these basis functions for the Mn atoms located in 3c positions are given and discussed in detail. A conclusion is made that the magnetic moments of Mn atoms in this intermetallic compound can be oriented along any crystallographic direction with the formation of collinear or canted magnetic structures. The total magnetic moments of separate Mn atoms in the unit cell of the crystal structure can coincide or differ in magnitude.

First-principles calculations of the structural and dynamical properties of ferroelectric YMnO3

We report the structural and dynamical properties of the ground state ferroelectric $P$6${}_{3}cm$ structure of hexagonal YMnO${}_{3}$. The lattice parameters, atomic positions, local magnetic moment of Mn atoms, band gap, and \ensuremath{\Gamma}-point phonons are calculated within the local spin-density approximation plus Hubbard $U$ term and the B1-WC hybrid functional. Our results are discussed in comparison to theoretical and experimental values available in the literature. Based on our first-principles calculations, we propose a reassignment of certain modes. We also discuss the relation between the phonon modes of the ferroelectric $P$6${}_{3}cm$ phase and those of the paraelectric $P$6${}_{3}$/mmc phase that condense at the phase transition.

First Principles Study of Half-metallic Properties at MnSb/GaSb(001) Interface

Density functional theory calculations are performed to study the structural, electronic and magnetic properties of hexagonal NiAs type and cubic zinc blende type MnSb structure and interface of zinc blende MnSb with GaSb(001). We used generalized gradiant approximation to calculate the exchange-correlation term in bulk and interface determination. The zinc blende structure of MnSb is found to be ferromagnetic half-metal with a total moment of 4 μB per formula unit. Results show that the half-metallicity character is preserved at MnSb/GaSb(001) interface. The magnetic moment of Mn atom in interface is reduced and the magnetic moment of the interface Sb atom is equal to the average of the corresponding bulk values in two sides of the interface. The band alignment properties are also computed and a rather large minority valance band offset of about 1.25 eV is obtained in this heterojunction.

MAGNETIC MAP OF MnNi ALLOYED MONOLAYER ON Cu(001) SUBSTRATE: AB-INITIO CALCULATIONS

In this work, a theoretical study of the structural, electronic and magnetic properties are presented for Mn 0.5 Ni 0.5 alloyed overlayer adsorbed on Cu (001) surface. The calculations were performed using the density functional theory (DFT) and the exchange-correlation potential was treated by the generalized gradient approximation (GGA). The system was fully relaxed except for the central layer, which yields to outward relaxations and inward Mn and Ni surface atoms, respectively in the ferromagnetic and antiferromagnetic configurations. The in-plane ferromagnetic configuration was found to be more stable than the antiferromagnetic one by 25 meV/atom. The local magnetic moments of Mn atoms were found to be about 4 μ B , whereas those of the Ni atoms where found to be 0.46 μ B .

Theoretical investigation of the effects of composition and atomic disordering on the properties of Ni 2Mn(Al 1− xGa x) alloy

The influences of composition and Mn–Ga/Al disordering on the magnetic and elastic properties of the Ni 2Mn(Al 1− x Ga x ) Heusler alloy are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The transition temperature from the completely disordered B2 phase to the ordered L2 1 phase, estimated by the use of Bragg–Williams–Gorsky approximation, is in excellent agreement with experiments. The site-occupancy in the partially disordered alloy is determined by comparing the free energies of the alloys with different site-occupation configurations. It is found that Mn atoms generally prefer to exchange with Al atoms for the alloy with low degree of disorder and low Ga concentration. With increasing degree of disorder and Ga concentration, Mn may exchange with Ga as well. The total magnetic moment of the completely ordered alloy exhibits a minimum around x = 0.7 due to the competition between the increasing magnetic moments of Mn atoms and the decreasing moments of Ni atoms with increasing x. For the partially disordered alloy, both total and local magnetic moments of Mn and Ni decrease linearly with increasing degree of disorder, and Ga atoms show significant magnetism. The shear moduli C′ of the alloys are calculated with respect to both x and the degree of disorder. The results show that C′ decreases with increasing x and degree of disorder. The dependence on composition and on the degree of disorder of the martensitic transition temperatures is discussed in terms of the calculated C′.

ChemInform Abstract: Recent Developments in Magnetism and Magnetic Materials

In the last decade we have obtained a deeper understanding of basic magnetism in alloys and a variety of new magnetic materials have been developed. In this review article two kinds of recent topics in these fields will be discussed. The first one is the magnetic properties of rare earth-3d transition intermetallics. After describing the magnetic properties of RMn2 very briefly, we discuss the magnetic properties of YMn2 in detail, particularly its magnetovolume effect which is closely related with the magnetic moment of Mn atoms below and above the magnetic transition temperature. Then, as an example of recent developments in soft magnetic materials, Fe-Ni-Cr alloys with very high permeability and low coercive force will be discussed including impurity effects on their magnetic properties.

Magnetic properties of Mn-rich Pd 2MnSn Heusler alloys

Pd 2Mn 1+ x Sn 1− x (0 ≤ x ≤ 0.30) alloys crystallize in the cubic L2 1 structure. The lattice parameter a decreases linearly with increasing Mn concentration x. X-ray powder diffraction patterns indicate that the excess Mn atoms occupy the vacant Sn sites. All alloys exhibit the ferromagnetic behavior. The pressure change of the magnetic moment per formula unit at 5 K for Pd 2MnSn is independent of pressure. The Curie temperature of Pd 2Mn 1+ x Sn 1− x (0 ≤ x ≤ 0.30) alloys increases linearly with increasing x. Magnetization measurements make clear that the magnetic moment of Mn atoms, which substitute for Sn sites, is coupled antiferromagnetically to the magnetic moment of Mn atoms on the ferromagnetic Mn sublattice.

Phase stability and magnetic properties of Ni 50Mn 50−xIn x Heusler-type alloys

The order–disorder transformation and the magnetic properties of Heusler-type Ni50Mn50−xInx ternary alloys were investigated. The B2/L21 order–disorder transformation temperatures are detected at about 800–1100 K. In the alloys with the L21 structure, while the spontaneous magnetization at 4.2 K monotonically decreases with increasing x, the Curie temperature is almost constant with x ⩽ 25 and decreases linearly with x > 25. This unique behavior is qualitatively explained by the concept of local magnetic moment of Mn atoms.

Metamagnetic behaviour under high magnetic fields in Ni50Mn50−xInx (x = 14.0 and 15.6) shape memory alloys

Magnetization measurements up to high magnetic fields of 56 T applied with a pulsed magnet were carried out for x = 14.0 and 15.6 in Ni50Mn50−xInx alloys. Metamagnetic behaviour from the nonmagnetic martensite phase to the ferromagnetic parent phase was observed even at x = 14.0, where no ferromagnetic phase exists in the entire temperature range under a low magnetic field. The spontaneous magnetization Is for x = 14.0 and 15.6 was deduced to be about 6.4 and 6.0 μB/f.u., respectively, and the Is increased with decreasing In concentration. This result strongly suggests that the magnetic moment of Mn atoms substituted at the In sites couples ferromagnetically to the magnetic moment of Mn atoms at the Mn sites.

Circularly polarized electroluminescence in LED heterostructures with InGaAs/GaAs quantum well and Mn δ-layer

Strong enhancement of electroluminescence intensity and high degree of its circular polarization (up to 50% at low temperature T=1.8 K and magnetic field B=9 T) are demonstrated in Schottky diodes with near contact InGaAs/GaAs quantum well and Mn δ-layer. High values of polarization degree are suggested to be due to effective exchange interaction of holes with magnetic moments of Mn atoms in the nearby δ-layer that is confirmed by peculiarities in the temperature dependence of resistance, typical to ferromagnetic semiconductors.

Theory of the piezomagnetic effect in Mn-based antiperovskites

Recent experimental and theoretical studies of the magnetoelectric (ME) effect in the nanocomposite structures and in laminates show an enhanced ME coefficient. These materials combine piezoelectric properties of the paramagnetic phase and piezomagnetic properties of the magnetic phase. We propose to fabricate heterostructures formed by piezoelectric materials and magnetic antiperovskites as magnetoelectric materials. We show that the magnetic structure of antiperovskite, such as ${\mathrm{Mn}}_{3}\mathrm{Ga}\mathrm{N}$, can be controlled by a small applied biaxial strain. The lowering of symmetry with the strain causes the local magnetic moments of Mn atoms to rotate from the trigonal ${\ensuremath{\Gamma}}^{5g}$ structure with symmetric curl of spin density in the (111) plane to a monoclinic symmetry structure. As a result, an appreciable net magnetization appears in the strained system.

Neutron diffraction study of the [formula omitted] ( [formula omitted], 0.7 and 1) compounds and the general description of the magnetic behavior of Mn in [formula omitted] and [formula omitted

The magnetic structures of the La 1 - x Pr x Mn 2 Si 2 ( x = 0.4 , 0.7 and 1) have been investigated by powder neutron diffraction between 2 and 308 K. According to magnetic measurements, the x = 0.4 sample shows a typical SmMn 2 Ge 2 -like magnetic behavior. Neutron diffraction indicates a canted antiferromagnetic structure below 130 K and a canted ferromagnetic structure above 240 K. Between 130 and 240 K, the canted ferromagnetic and antiferromagnetic structures coexist. Since the magnetic moments of Mn atoms, the unit cell parameters and the scale parameters of the canted antiferromagnetism and canted ferromagnetism are highly correlated between 130 and 240 K, a special refinement procedure was introduced. The critical Mn–Mn value was determined as 2.87 A ˚ , and the spontaneous volume change and linear magnetostriction are derived. Neutron diffraction revealed a canted antiferromagnetic structure for La 0.3 Pr 0.7 Mn 2 Si 2 . A canted antiferromagnetic structure was also detected for PrMn 2 Si 2 by neutron diffraction in contrast to previous reports of a collinear arrangement. The present results are compiled together with previous ones on RMn 2 Ge 2 and RMn 2 Si 2 (R: Y, La and rare-earth) compounds in two magnetic phase diagrams. These two graphics summarize the general magnetic behavior of Mn in the RMn 2 Ge 2 and RMn 2 Si 2 compounds.

Physical and electronic structure and magnetism ofMn2NiGa: Experiment and density-functional theory calculations

Both experimental and theoretical studies have been carried out to study the structure and magnetic properties of Mn2NiGa alloys. We have found, instead of forming L2(1) structure where both A and C sites are occupied by Mn atoms, the alloy favor a structure where the C site is occupied by Ni atoms and Mn atoms at A and B sites. The electronic structures of both cubic austenite and tetragonal martensite Mn2NiGa were calculated by self-consistent full-potential linearized-augmented plane-wave (FP-LAPW) method. Austenite Mn2NiGa materials show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn atoms at A and B sublattices. The magnetic moment of Mn atoms decrease greatly upon martensitic transformation to a tetragonal structure with a 50% reduction in Mn moments at the A site and almost completely suppressed Mn moments at B sites. Consequently, martensite Mn2NiGa alloys show ferromagnetic coupling. Different magnetic orderings in martensite and austenite also lead to very different temperature dependence, with which the abnormal behavior of magnetization upon martensitic transformation can be understood. In the off-stoichiometric samples with composition between Ni2MnGa and Mn2NiGa, we show that additional Mn atoms that substitute for Ni atoms in Ni2MnGa have the same magnetic behaviors as Mn in Mn2NiGa phase, which successfully explains the dependence of the magnetization on Mn composition.

X-ray2pphotoelectron andLαresonant x-ray emission spectra of the3dmetals inNi2MnZ(Z=In,Sn,Sb)Heusler alloys

Magnetic and chemical bonding effects in Heusler alloys ${\mathrm{Ni}}_{2}\mathrm{Mn}\mathrm{In}$, ${\mathrm{Ni}}_{2}\mathrm{Mn}\mathrm{Sn}$, and ${\mathrm{Ni}}_{2}\mathrm{Mn}\mathrm{Sb}$ were studied by soft x-ray spectroscopy. Exchange splitting detected in Mn $2p$ core-level x-ray photoelectron spectra and an increase of the Mn ${L}_{\ensuremath{\beta}}∕{L}_{\ensuremath{\alpha}}$ intensity ratio in nonresonant x-ray emission spectra show that atomic magnetic moment at Mn is higher than that of pure metal. Spin polarized density of states calculations and comparative analysis of Mn and Ni ${L}_{\ensuremath{\alpha}}$ resonant x-ray emission spectra (RXES) demonstrate that the spin splitting in Mn $3d$ shell is larger than in Ni $3d$ shell. The $d\text{\ensuremath{-}}d$ transitions observed in ${L}_{\ensuremath{\alpha}}$ RXES of Mn and Ni are suggested to be more intensive for Mn than for Ni valence electrons when initiated by off-resonant excitations. Experimental findings are supported by photoelectron spectra calculations and developed two-step model of resonant x-ray emission. The interplay between Mn ${L}_{\ensuremath{\alpha}}$ RXES and calculated magnetic moments of Mn atoms in alloys as a function of the type of $Z$ element is discussed.