Transition Metal Magnetic Moment Research Articles

Magnetic structure and pressure-induced spin-crossover in Me3B2O6 (Me = Mn, Fe, Co, Ni) kotoites: Representation analysis and DFT calculations

The magnetic and electronic properties of transition metal borates Me3B2O6 (Me = Mn, Fe, Co, Ni) with kotoite structure have been investigated at ambient and high pressures via a combination of representation analysis and density functional theory (DFT + U) calculations. Several magnetic configurations corresponding to the different irreducible representations have been considered. The total-energy calculations reveal that the magnetic ground state of Me3B2O6 kotoites is composition-dependent. The lowest energy magnetic phase of manganese and nickel kotoites is characterized by the antiferromagnetic ordering of the transition metal magnetic moments along the c- axis and along the b-axis for cobalt and iron kotoites. The magnetic cell of Ni3B2O6 kotoite corresponds to k = (1/2, 0, 1/2) vector and four time larger than the unit cell. The calculated exchange constants indicate the competition between ferromagnetic and antiferromagnetic interactions. At a critical pressure, Me ions undergo a high-spin to low-spin state crossover. This magnetic moments collapse is analyzed in terms of change in electronic structure under pressure.

A magnetic study of the HoCo12-xFexB6 ferrimagnetic compounds

The effects of Fe substitution on the structural and magnetic properties of the HoCo12-xFexB6 (0 ≤ x ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi12B6-type structure, the lattice constants increasing linearly with x. These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for x = 0–105 K for x = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition.

Enhanced Magnetization of Cobalt Defect Clusters Embedded in TiO2−δ Films

High magnetizations are desirable for spintronic devices that operate by manipulating electronic states using built-in magnetic fields. However, the magnetic moment in promising dilute magnetic oxide nanocomposites is very low, typically corresponding to only fractions of a Bohr magneton for each dopant atom. In this study, we report a large magnetization formed by ion implantation of Co into amorphous TiO2-δ films, producing an inhomogeneous magnetic moment, with certain regions producing over 2.5 μB per Co, depending on the local dopant concentration. Polarized neutron reflectometry was used to depth-profile the magnetization in the Co:TiO2-δ nanocomposites, thus confirming the pivotal role of the cobalt dopant profile inside the titania layer. X-ray photoemission spectra demonstrate the dominant electronic state of the implanted species is Co0, with a minor fraction of Co2+. The detected magnetizations have seldom been reported before and lie near the upper limit set by Hund's rules for Co0, which is unusual because the transition metal's magnetic moment is usually reduced in a symmetric 3D crystal-field environment. Low-energy positron annihilation lifetime spectroscopy indicates that defect structures within the titania layer are strongly modified by the implanted Co. We propose that a clustering motif is promoted by the affinity of the positively charged implanted species to occupy microvoids native to the amorphous host. This provides a seed for subsequent doping and nucleation of nanoclusters within an unusual local environment.

Rapidly convergent cluster expansion and application to lithium ion battery materials

The convergence of a cluster expansion for lithium transition-metal (TM) oxides is improved by explicit treatment of TM magnetic moments. The approach is applied to layered $\mathrm{LiC}{\mathrm{o}}_{y}\mathrm{N}{\mathrm{i}}_{1\ensuremath{-}y}{\mathrm{O}}_{2}$ (NC). The ground state and low-lying excited state structures are identified, and the distribution of TM ions and magnetic moment in those structures is investigated to explain the origin of Ni-antisite ions and Jahn-Teller distortion. The developed model also reveals the mechanisms governing the atomic arrangement of NC, including in-plane Co-Co vs Co-Ni competition, magnetic frustration vs disproportionation competition, and cationic interactions spanning adjacent layers.

Electronic and magnetic properties of NiMn1−xHoxSb compounds

AbstractWe study the effects of holmium doping in the half‐Heusler compound NiMnSb. Band structure calculations show that the half‐metallic properties are completely conserved if holmium atoms substitute the manganese ones. The antiparallel coupling of Ho and transition metal magnetic moments was found to be more favorable. The magnetization measurements are in agreement with the results of the structural and XPS analysis and confirm that the holmium atoms occupy lattice sites. There is a very good agreement between the experimental magnetic moments determined at 4.2 K and the calculated ones in the case of antiferromagnetic coupling between the Ho and transition metal magnetic moments.

StrongK-edge Magnetic Circular Dichroism Observed in Photon-in–Photon-out Spectroscopy

A large enhancement of the x-ray magnetic circular dichroism is observed at the iron K absorption preedge of magnetite. This is achieved by performing resonant inelastic x-ray scattering (RIXS) experiments with a 2p hole in the final state of the second-order optical process. We measured and calculated the full 1s2p RIXS planes for opposite helicities of the incoming circularly polarized x rays. The crystal field multiplet calculations show that the enhancement arises from 2p-3d Coulomb repulsions and 2p and 3d spin-orbit coupling. The observed magnitude of the RIXS magnetic circular dichroism effect is ∼16%. This opens up new opportunities for a broad range of research fields allowing for truly bulk-sensitive, element-, and site-selective measurements of 3d transition metal magnetic moments and their ordering using hard x-ray photons.

A structural, magnetic, and Mössbauer spectral study of the TbCo4−xFexB compounds with x=, 1, and 2

The TbCo4−xFexB compounds with x=0, 1, and 2 have been investigated by x-ray and neutron diffraction, magnetic measurements, and iron-57 Mössbauer spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase of approximately 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mössbauer spectra of the TbCo4−xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of approximately 1.7μB, and small iron hyperfine fields of approximately 16 T. The compensation temperature of the TbCo4−xFexB compounds decreases continuously from 400 to 350 K between x=0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects the strong hybridization of the 3d orbitals of the 6i site transition metal with the boron 2p orbitals.

Perpendicular magnetic anisotropy in TbFeCo films studied by magnetic Compton scattering

Magnetic Compton profiles (MCPs) of TbFeCo amorphous films have been measured from a viewpoint of perpendicular magnetic anisotropy (PMA). Analysis of anisotropies of the MCPs has shown that anisotropies of wave functions are small in both a PMA film and an isotropic magnetization (IM) film. Element selective analysis of the MCPs has shown that a Tb magnetic moment and a magnetic moment of 3d transition metal (TM) are coupled antiparallel in the PMA film. In the case the IM film, the magnetic moment of 3d TM tends to align toward the magnetic field but the Tb magnetic moment distributed to random orientations. The PMA natures reflect the magnetic structures of the Tb magnetic moment and the 3d TM magnetic moment in the TbFeCo films.

Review on the Influence of Hydrogen on the Magnetism of Alloys Based on Rare Earth—Transition Metal Systems

AbstractFor Abstract see ChemInform Abstract in Full Text.

Review on the influence of hydrogen on the magnetism of alloys based on rare earth-transition metal systems

Extensive studies of the magnetism of metal hydrides have been carried out in the last three decades. Hydrogenation of metals and intermetallic compounds frequently results in a striking alteration of their electronic and magnetic characteristics and leads to some extraordinary new features. In materials which contain a transition metal, the effect of hydrogen on the magnetic properties is twofold: Firstly, from the band structure point view, since hydrogen contributes two states and only one electron, the Fermi level, and hence the transition metal magnetic moment, is affected. Secondly hydrogen absorption results in increased lattice dimensions, which influences the strength of the interaction between magnetic ions. One of the most striking effects of hydrogen absorption is observed in the intermetallic compounds Th 7Fe 3H 30. In this instance, the parent material is a superconductor, but upon hydrogenation it becomes magnetically ordered. The class of compounds based on R 6T 23 (R=rare earth, T=Mn, Fe) has shown dramatic magnetic structure change upon hydrogenation. For example, on hydrogenation, Y 6Mn 23 transforms from a ferrimagnet to an antiferromagnet. The influence of hydrogen on the magnetic properties and crystal structure of rare earth-transition metal-based intermetallic compounds with RT 2, RT 3, R 6T 23, R 2T 14B and R 6T 13X structure type (R=rare earth, T=Fe, Co or Mn and X=the third, fourth and fifth group of elements in the periodic table) is reviewed.

Calculation for core-s-XPS of transition metals on graphite

A few years ago, the appearance of surface magnetism of vanadium upon graphite was pointed out experimentally and was assumed to be quenched after exposure to CO pollutant: only for freshly evaporated V clusters on graphite, a satellite structure had been found in the V 3s-XPS spectrum and it was attributed to the presence of magnetic moments on the V surface. More recently the appearance of magnetism was observed (by means of other techniques) in a Ru monolayer grown laterally on the C(0001) graphite surface. In the present paper, we extend the impurity Anderson model for the calculation of transition metal core-s-XPS spectra by taking into account the exchange terms, especially between the core hole spin and the transition metal magnetic moment. Our results on core-s-XPS are discussed in terms of the various parameters entering the present model Hamiltonian and a new interpretation of the experimental V 3s-XPS spectrum is proposed.

X-ray-absorption edge shifts in rare-earth-transition-metal compounds.

X-ray-absorption K-edge shifts of cobalt have been measured in ${\mathrm{Y}}_{2}$${\mathrm{Co}}_{17}$, ${\mathrm{YCo}}_{5}$, and ${\mathrm{YCo}}_{3}$ compounds whose crystal structures are derivatives of the ${\mathrm{CaCu}}_{5}$ structure. The edge shifts vary monotonically with the Y:Co ratio. We compare them with Fe, Y, and Ce edge shifts determined for several other related materials, including ${\mathrm{Y}}_{2}$${\mathrm{Fe}}_{17}$, ${\mathrm{Ce}}_{2}$${\mathrm{Fe}}_{17}$, and ${\mathrm{CeCo}}_{2}$. In all cases, the shifts are the same sign, a fact that points to the absence of a significant uncompensated charge transfer from one elemental constituent to another. Identifying the edge shifts as core-level shifts, we find that the Watson-Hudis-Perlman charge-compensation model is applicable to these systems; estimates of the model parameters lead to small net charge transfers consistent with available M\"ossbauer effect measurements. Our results show that there is no straightforward relation between the transition-metal magnetic moment and either charge transfer or corresponding absorption edge shift, which implies that the variation of the moment with stoichiometry in these materials is not governed by the filling of rigid transition-metal bands.

3d magnetism in R-M and R 2M 14B compounds (M = Fe, Co; R =rare earth)

In this paper, 3d magnetism in the R 2M 14B-type (M = Fe, Co) compounds is examined in conjunction with the magnetic properties of binary RM compounds. The decrease of the transition metal magnetic moment μ M as a function of the amount of rare earth alloyed is discussed in terms of the Friedel interpretation of the Slater-Pauling curve for transition metal alloys. The exchange interactions in the Co alloys are mainly dependent on the value of the Co magnetic moment; in Fe alloys, they are essentially determined by local environment effects. In Y-Fe and Lu-Fe compounds, it is shown that the molecular field coefficient n FeFe between Fe atoms decreases as the Fe coordination number increases. From the increase in T c with x in R 2(Fe 1− x Co x ) 14B and R 2(Fe 1− x Co x ) 17 alloys it appears that the FeCo exchange interactions are as large as the CoCo ones.

非晶質ＴｂＦｅＣｏ膜の磁気特性

Some rare earth-transition metal amorphous alloy films prepared by sputtering or evaporation have uniaxial anisotropy perpendicular to the film plane. These amorphous magnetic films are expected as magneto-optical memory material. Although amorphous TbFe magnetic film has a high coercivity and low Curie temperature, the signal level of magneto-optical readout is lower than other amorphous magnetic films. Therefore the higher magneto-optic properties (higher Kerr rotation angle) is desired.For obtaining a higher Kerr rotation angle, amorphous TbFeCo films was studied. It is found that the suitable Co substitution for Fe caused the increase of the Kerr rotation angle of amorphous TbFeCo magnetic films and θk at 633 nm and 840 nm have peak values 0.42° and 0.52° at X=50 in Tb21(Fe100-XCoX)79, respectively.Curie temperature of TbFeCo increased linearly with increasing Co concentration and its slope was about 3.6-4 degree.From the temperature dependence of the Kerr rotation angle it is conjectured that, in Tb21(Fe100-XCoX)79, the transition metal magnetic moment at 0 k becomes a maximum at near X=30 as well as a maximum saturation magnetization in FeCo binary alloy.

Interpretation of the magnetic properties of pseudobinarySm2(Co,M)17compounds. II. Magnetization

The data available from paper I of this series offer the opportunity to ascertain the cause of the variations in both ${\mathrm{Sm}}^{3+}$ and transition-metal magnetic moments upon substitution of Co by Fe, Mn, and Cr in ${\mathrm{Sm}}_{2}$${\mathrm{Co}}_{17}$. The exchange- and crystal-field parameters derived from the magnetocrystalline anisotropy are used in the calculation of the ${\mathrm{Sm}}^{3+}$ ionic moment in fields of hexagonal symmetry. Both the moment reduction at O K and the change in the temperature at which the moment changes sign are found to agree well with the values observed experimentally. The ${\mathrm{Sm}}^{3+}$ ion changes to an $L+S$ type ion at higher temperatures but not at absolute zero. The itinerant-electron moment varies in a manner indicative of electron donation to $3d$ band in the presence of virtual bound states. The ${\mathrm{Sm}}_{2}$${\mathrm{Co}}_{17}$ crystal structure becomes unstable at high $3d$-electron concentrations.

Magnetic properties and electronic structure of rare earth-transition metal intermetallic compounds

A model for the electronic structure of the RxMy intermetallic compounds is proposed in which the s electrons are spread over the crystal and the d states are mostly localized on the transition metal sites, the degree of localization varying from 3d to 4d and 5d. The authors distinguish between two cases: (i) magnetism driven by the localized f moments (e.g. GdCo2), and (ii) magnetism sustained by the d band (e.g. LuFe2). These two situations are discussed in terms of an effective s-d coupling and an s-f exchange; the transition metal magnetic moment in (ii) is calculated using a simple model. The rare earth isomer shifts and the paramagnetic susceptibility of the compounds are also considered; the excess h.f. fields in the RFe2 compounds may be understood within this picture. Finally, it is shown that the s-d hybridization mechanism may account for the observed effective s-d coupling.