Net Spin Moment Research Articles

Magnetic Properties and Electronic Configurations of Mn Ions in the Diluted Magnetic Semiconductor Ba1−xKx(Zn1−yMny)2As2 Studied by X-ray Magnetic Circular Dichroism and Resonant Inelastic X-ray Scattering

The magnetic properties and the electronic excitations of the new diluted magnetic semiconductor Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ have been studied by x-ray magnetic circular dichroism (XMCD) and resonant inelastic x-ray scattering (RIXS) at the Mn $L_{2,3}$ edge. The sum rule analysis of the XMCD spectra yields the net spin moment of $0.45\mu_{\text{B}}$/Mn and the small orbital moment of $0.05\mu_{\text{B}}$/Mn. This indicates that the Mn atoms are in the high-spin configurations of $d^{5}$, whereas the presence of competing ferromagnetic and antiferromagnetic interactions between the Mn ions reduces the net spin moment. RIXS spectra show broad peaks from 1 to 6 eV energy loss, which originate from the $d$-$d$ crystal field excitations of the Mn ions. Based on a comparison of the RIXS line shapes with those of Ga$_{1-x}$Mn$_{x}$As, we conclude that the ground state of Mn in Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ consists not only of the charge-transferred $3d^{5}\underline{L}$ electron configuration ($\underline{L}$: ligand hole) with weakly bound holes as in Ga$_{1-x}$Mn$_{x}$As, but also of the pure $3d^{5}$ configuration with free holes.

Magnetic response of Nd-doped nickel ferrites using magnetic Compton scattering and XPS measurements

Spin-polarized electron momentum densities of Nd-doped nickel ferrites (Ni1−xNdxFe2O4 where , 0.24) at 8 and 300 K temperatures are presented. The measurements have been made using the magnetic Compton scattering set-up available at SPring-8, Japan. The site-specific spin moments which contribute to the formation of the total spin moment are deduced by decomposition of the magnetic Compton profile (MCP) into constituent profiles. An increase in the spin moment at Fe site and a reduction at Ni site with Nd doping, as revealed by MCP data, are explained on the basis of the cationic redistribution at octahedral and tetrahedral sites using x-ray photoelectron spectroscopy (XPS) analysis. The XPS measurements suggest the emergence of Fe2+ ions in Nd-doped samples to maintain the charge neutrality. It is found that the net spin moment at the Nd site is antiparallel to that at Ni and Fe sites. The orbital magnetic moment (deduced from the difference of magnetic Compton and total magnetization data) is also discussed.

Interacting nanoscale magnetic superatom cluster arrays in molybdenum oxide bronzes.

In this study, we examine several reduced ternary molybdates in the family of yellow rare earth molybdenum bronzes produced by electrochemical synthesis with composition LnMo16O44. These compounds contain an array of electrically isolated but magnetically interacting multi-atom clusters with composition Mo8O36. These arrayed superatom clusters support a single hole shared among the eight molybdenum atoms in the unit, corresponding to a net spin moment of 1μB, and exhibit magnetic exchange between the units via the MoO4 tetrahedra (containing Mo6+ ions) and the LnO8 cubes (containing Ln3+ ions). The findings presented here expand on the physics of the unusual collective properties of multi-atom clusters and extend the discussion of such assemblages to the rich structural chemistry of molybdenum bronzes.

Density functional studies of the magnetic properties in nitrogen doped TiO 2

The ferromagnetic and antiferromagnetic states of anatase and rutile TiO 2 doped with N atoms at oxygen sites were investigated by density functional theory calculations for a number of model N-doped TiO 2 structures. The each N dopant at an O site exists as an N 2− ion with net spin moment of 1.0 μ B. In general, the spin exchange coupling between the spin moments of two N dopants is strong when the two dopants are coordinated to a common Ti atom, and whether the coupling between the two N atoms is ferromagnetic or antiferromagnetic in such a case depends on the ∠N–Ti–N angle.

Magnetism in assembled and supported silicon endohedral cages: First-principles electronic structure calculations

First principles electronic structure calculations on a free CrSi12 cluster, a CrSi12 2 dimer, and CrSi12 clusters supported on Si 111 surfaces have been carried out within a gradient corrected density functional formalism using a supercell approach. The ground state of CrSi12 is a Cr centered hexagonal biprism of Si atoms in which the Cr spin moment is completely quenched. As two CrSi12 motifs are brought together, they form different composite units depending on initial direction of approach and, in most cases, the composite cluster is found to have a net spin moment. Cluster assemblies obtained by depositing CrSi12 motifs on a Si 111 surface exhibit similar finite spin moments for several initial directions of approach. An analysis of the electronic states shows that the origin of the magnetic moment lies in those Cr d-states that do not mix with silicon sp states. The studies suggest the possibility of forming silicon-based magnetic semiconductors through such assemblies.

Near compensated half-metal in Sr2NiOsO6

The electronic and magnetic properties of tetragonal double perovskite Sr(2)NiOsO(6) were studied by use of the density functional theory and including the spin-orbit coupling. Compensated half-metal is found if the spin-orbit coupling is not considered. Spin-orbit coupling induces orbital moments on both Ni and Os, making Sr(2)NiOsO(6) a near compensated half-metal. Ferromagnetic phase is slightly favored over antiferromagnetic phase (by 4 meV). The small energy difference also suggests that both phases are competitive for the ground state. At ferromagnetic phase, the calculated net magnetic moment is 3.53 micro(B), in good agreement with experimental value of 3.44 micro(B). At antiferromagnetic phase, the net magnetic moment is 0.69 micro(B), in which the contribution from the net spin moment is 0.09 micro(B).

Half semimetallic antiferromagnetism in theSr2CrTO6system(T=Os,Ru)

Double perovskite ${\mathrm{Sr}}_{2}\mathrm{Cr}\mathrm{Os}{\mathrm{O}}_{6}$ is (or is very close to) a realization of a spin-asymmetric semimetallic compensated ferrimagnet, according to first principles calculations. This type of near-half metallic antiferromagnet is an unusual occurrence, and more so in this compound because the zero gap is accidental rather than being symmetry determined. The large spin-orbit coupling (SOC) of osmium upsets the spin balance (no net spin moment without SOC): it reduces the Os spin moment by $0.27{\ensuremath{\mu}}_{B}$ and induces an Os orbital moment of $0.17{\ensuremath{\mu}}_{B}$ in the opposite directions. The effects combine (with small oxygen contributions) to give a net total moment of $0.54{\ensuremath{\mu}}_{B}$ per cell in ${\mathrm{Sr}}_{2}\mathrm{Cr}\mathrm{Os}{\mathrm{O}}_{6}$, reflecting a large impact of SOC in this compound. This value is in moderately good agreement with the measured saturation moment of $0.75{\ensuremath{\mu}}_{B}$. The value of the net moment on the Os ion obtained from neutron diffraction ($0.73{\ensuremath{\mu}}_{B}$ at low temperature) differs from the calculated value $(1.14{\ensuremath{\mu}}_{B})$. Rather surprisingly, in isovalent ${\mathrm{Sr}}_{2}\mathrm{Cr}\mathrm{Ru}{\mathrm{O}}_{6}$, the smaller SOC-induced spin changes and orbital moments (mostly on Ru) almost exactly cancel. This makes ${\mathrm{Sr}}_{2}\mathrm{Cr}\mathrm{Ru}{\mathrm{O}}_{6}$ a ``half (semi)metallic antiferromagnet'' (practically vanishing net total moment) even when SOC is included, with the metallic channel being a small-band-overlap semimetal. Fixed spin moment (FSM) calculations are presented for each compound, illustrating how they provide different information than in the case of a nonmagnetic material. These FSM results indicate that the Cr moment is an order of magnitude stiffer against longitudinal fluctuations than is the Os moment.

ChemInform Abstract: Magnetic and Electronic Properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by First‐Principles Density Functional Calculation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Magnetic and Electronic Properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by First-Principles Density Functional Calculation

The electronic and magnetic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 are investigated by the use of the full-potential linearized augumented plane wave (FPLAPW) method. The calculated results indicate that CaCu3Cr4O12 is a ferrimagnetic and half-metallic compound, in good agreement with previous theoretical studies. CaCu3Cr2Sb2O12 is a ferrimagnetic semiconductor with a small gap of 0.136 eV. In both compounds, because Cr4+ 3d (d2) and Cr3+ 3d (d3) orbitals are less than half filled, the coupling between Cr-Cu is antiferromagnetic, whereas that between Cu-Cu and Cr-Cr is ferromagnetic. The total net spin moment is 5.0 and 3.0 microB for CaCu3Cr4O12 and CaCu3Cr2Sb2O12, respectively. In CaCu3Cr4O12, the 3d electrons of Cr4+ are delocalized, which strengthens the Cr-Cr ferromagnetic coupling. For CaCu3Cr2Sb2O12, the doping of nonmagnetic ion Sb5+ reduces the Cr-Cr ferromagnetic coupling, and the half-filled Cr3+ t2g (t2g3) makes the chromium 3d electrons localized. In addition, the ordering arrangement of the octahedral chromium and antimony ions also prevents the delocalization of electrons. Hence, CaCu3Cr2Sb2O12 shows insulating behavior, in agreement with the experimental observation.

Mn,Cd-metallothionein-2: A room temperature magnetic protein

Naturally occurring metallothionein (MT) is a metal binding protein, which binds to seven Zn 2+ through 20 conserved cysteines and forms two metal binding clusters with a Zinc-Blende structure. We demonstrate that the MT, when substituting the Zn 2+ ions by Mn 2+ and Cd 2+, exhibits magnetic hysteresis loop observable by SQUID from 10 to 330 K. The magnetic moment may have originated from the bridging effect of the sulfur atoms between the metal ions that leads to the alignment of the electron spins of the Mn 2+ ions inside the clusters. The protein backbone may restrain the net spin moment of Mn 2+ ions from thermal fluctuation. The modified magnetic-metallothionein is a novel approach to creating molecular magnets with operating temperatures up to 330 K.

Classical Stern-Gerlach profiles ofMn5andMn6clusters

${\mathrm{Mn}}_{5}$ and ${\mathrm{Mn}}_{6}$ clusters have recently been found to exhibit Stern-Gerlach profiles marked by a central peak that broadens with the increasing field gradient. The profiles neither exhibit a reminiscence of space quantization as observed through a splitting of beams for the case of free atoms, nor a net deflection characteristic of superparamagnetic relaxations observed in other transition metal clusters. It is proposed that this new behavior results from a weak coupling of localized atomic moments. ab initio electronic structure studies are carried out to show that a ${\mathrm{Mn}}_{5}$ cluster has isomers with spin magnetic moments of $3\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, $13\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, and $23\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ while a ${\mathrm{Mn}}_{6}$ cluster has isomers with moments of $2\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, $8\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, $16\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, and $26\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, respectively. The isomers can be obtained by sequential turning of the local atomic moments starting from the ferromagnetic state and can be seen in the negative ion photoelectron spectra of the anions. The weak coupling of the atomic moments, however, leads to unconventional spin dynamics that result in classical broadening of the Stern-Gerlach profiles and lower apparent magnetic moments. The theoretical results illustrate how a combination of the negative ion photodetachment spectroscopy and Stern-Gerlach profiles can provide information on the net spin moment, interatomic spin coupling, and spin dynamics.

Magnetoelectronic properties of a ferrimagnetic semiconductor: The hybrid cupromanganiteCaCu3Mn4O12

The mixed manganite-cuprate CaCu3Mn4O12 is found, using density functional methods, to be a narrow gap (90 meV calculated) ferrimagnetic semiconductor. Cu (formally S=1/2) antialigns with Mn (formally S=3/2), and the net spin moment is 9 \mu_B consistent with the formal spins. Holes have Cu d_{xy}-O p_{\sigma} (i.e. antibonding dp\sigma) character with spins aligned antiparallel to the net magnetization; electrons have the opposite spin and have mixed Cu d_{xy} - Mn e_g character. Thermally excited electrons and holes will each be fully spin polarized, but in opposite directions. The properties of this material are strongly tied to the distorted quadruple perovskite structure, which is closely related to the skutterudite structure. The observed resistivity, magnetoresistance, and magnetization are discussed in terms of our results.

Electronic structure study of the magnetoresistance materialCaCu3Mn4O12by LSDA andLSDA+U

The electronic structure of the large low-field magnetoresistance material ${\mathrm{CaCu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ is calculated by using the local-spin-density approximation (LSDA) and on-site Coulomb interaction correction $(\mathrm{LSDA}+\mathrm{U})$ to the $3d$ electronic states of Cu and Mn ions. The results obtained suggest a strong ionic character of this material despite a presence of a partial Mn-O covalence effect. Three Cu ions per formula cell have their respective half-filled orbitals ${d}_{\mathrm{xy}},{d}_{\mathrm{yz}},$ and ${d}_{\mathrm{xz}}$ due to their different local crystal environments. Four Mn ions per formula cell have nearly the same oxygen coordinations. As a consequence, the spin-up ${t}_{2g}$-like orbitals ${(d}_{\mathrm{xy}}{,d}_{\mathrm{yz}},$ and ${d}_{\mathrm{xz}})$ are almost full-filled, while the spin-up ${e}_{g}$-like orbitals ${(d}_{{3z}^{2}\ensuremath{-}{r}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ are partially occupied due to a finite $\mathrm{pd}$ hybridization. And it is shown that the sublattices of Cu ions and Mn ones are both aligned in ferromagnetic order, while these two sublattices are coupled antiferromagnetically, thus giving a net spin moment of 9 ${\ensuremath{\mu}}_{B}$ per formula. The $\mathrm{LSDA}+\mathrm{U}$ calculation yields a semiconducting solution, which is improved upon a half-metallic state given by the LSDA calculation and consistent with an experimental measurement.

Effect of exchange coupling of polycrystalline antiferromagnetic layers on the magnetization behavior of soft magnetic layers

The complementary nature of the exchange bias field and the coercivity enhancement in ferromagnetic (F)-antiferromagnetic (AF) exchange-coupled layer systems is explained based on an extended Fulcomer and Charap's model, in which the directional distribution of the easy axes plays a decisive role in governing the magnetization behaviors. The model was further extended to deal with the AF-layer thickness ranging from zero to infinity taking into account of Neel's spin fanning model. A comprehensive explanation of the influence of exchange coupling on the magnetization behavior of the F-layer is given. It is shown that a rotational magnetization process is inherent for the samples in which the exchange coupling effect is dominant. The same model explains the temperature dependence of the exchange bias field and coercivity and the memory effect observed after annealing. The varieties of phenomena are mostly ascribed to the existence of distribution in the magnetic properties, net spin moment at the AF-grain surface and AF-grain size.

Magnetization Behavior in Ferro/Antiferromagnetic Exchange-Coupled Films (Review)

The complementary nature of the exchange-bias field and coercivity enhancement in ferromagneic (F) antiferromagnetic (AF) exchange-coupled layer systems is explained based on an extended Fulcomer & Charap's model, in which the directional distribution of the easy axes plays a decisive role in governing the magnetization behaviors. The model was further extended to deal with the AF-layer thickness ranging from zero to infinity, taking into account of Neel's spin-fanning model. A comprehensive explanation of the influence of exchange coupling on the magnetization behavior of the F-layer is given. It is shown that a rotational magnetzation process is inherent for the samples in which the exchange coupling effect is dominant. Varieties of phenomena are mostly ascribed to the existence of distribution in the magnetic properties, net spin moment at the AF-grain surface and AF-grain size.

First Principles Description of the Valence States in Manganese Oxides

AbstractFirst principles periodic Hartree‐Fock calculations of Li:MnO, LixMnO2 and CaMnO3 are reported from which direct evidence is presented to indicate that the valence state of Mn remains essentially d5 throughout the series. The net spin moment on Mn, on the other hand, follows that convential change from ∼5μB to ∼3μB associated with the valence states Mn(II), Mn(III), Mn(IV).

First-principles description of the valence charge states in rutile MnO2

First-principles periodic Hartree–Fock calculations of the ground and first ionised and electron-addition states of rutile MnO 2 are reported from which the integrated charge- and spin-density distributions provide direct evidence that the charge state of Mn is essentially d5, as it is in MnO, and remains so with electron removal or addition. The net spin moment on Mn, on the other hand, is ca. 3 µ B , which is that normally associated with the Mn IV valence state, indicating that the unpaired d5 electron density is delocalised. This, together with the sign and magnitude of the overlap population, suggests strong covalency in this system in terms of p–d hybridisation.

The effect of volume on magnetization in RxY1−xCo2 pseudobinaries (abstract)

There is experimental1 and theoretical2 evidence that the cubic Laves phase compound YCo2, paramagnetic at its equilibrium volume, will become ferromagnetic with only a slight increase in volume. This volume sensitivity of Co-containing Laves phase compounds must therefore be considered when addressing the problem of the origin of the Co magnetic moment in pseudobinaries RxY1−xCo2, where R is any rare earth element with a net spin moment. In this paper we augment the itinerant picture describing the effect of the rare earth spin on the Co magnetization3 by taking into account the changes in volume brought about by the substitution of the rare earth for yttrium. We obtained the coefficients of the Landau expansion of the free energy by fitting the expansion to the calculated energy versus moment curves of YCo2 for various volumes.2 (These energies were calculated in Ref. 2 using the fixed-spin-moment method, within the local-spin-density approximation). Thus, for example, the substitution of Gd forces the formation of Co moments not only because of the Gd spin, but because of the increase in latttice constant, whereas the rare earths heavier than Tb have smaller lattice constants and are less likely to induce a moment on the Co sublattice. Results are presented for the critical fields necessary for magnetic ordering and for the Co magnetic moment as a function of the rare earth substitution.

Magnetic x-ray scattering

Developing improved magnetic materials for purposes from bombarding our eardrums with ever more faithfully reproduced taped sound to enhancing the storage capacity of computer disk drives, depends on a fundamental understanding of the net spin and orbital moment of electrons and their combination to produce bulk magnetisation. Studies of the spatial distribution of magnetisation in crystals have until now been the province of neutron rather than x-ray scattering.

Photoemission and magnetic effects in NaCrS2

X-ray and angle-resolved ultraviolet photoemission data on the layered compound NaCrS2 are presented and related to the electronic structure. The data indicate that the Cr 3d electrons are essentially localised and give rise to a multiplet splitting of the Cr 3s emission line; the magnitude of the splitting is discussed in terms of the magnetic properties of the material and the net spin moment of the Cr ions.