Ferrimagnetic Moment Research Articles

Experimental and first-principles investigation on magnetic properties and electronic structure in half-metallic Mn-Co-V-Al Heusler alloy

We report a systematic experimental and theoretical study of half-metallic Heusler alloys Mn2V1−xCoxAl (x = 0, 0.25, 0.5, 0.75, 1). In this study, using the arc-melting method and optimizing annealing temperatures, we succeed to synthesize Mn2V1−xCoxAl (x = 0, 0.25, 0.5, 0.75, 1) alloys with evident L21 (or XA) order. A near compensated ferrimagnetic moment of 0.02 μB/f.u. at 5 K is observed with the Co concentration of 0.5 which is consistent with the S-P rule. In addition, we systematacially investigate the effects of Co concentration on electronic structure of Heusler alloys Mn2V1−xCoxAl (x = 0, 0.25, 0.5, 0.75, 1) using first-principles calculations, and found that the half-metallic characteristic persists for all Co concentrations. In line with our experimental results, employing appropriate atomic site occupation, we obtained a full compensated ferrimagnetic moment of 0 μB/f.u. for stoichiometric Mn2V0.5Co0.5Al alloy. In addition, the robustness of half-metallic properties for compensated ferrimagnet Mn2V0.5Co0.5Al with the variation of atomic disorder are investigated and the results indicate that the Mn-Al swapping weakly destroys the half-metallic properties and the compensated ferrimagnet Mn2V0.5Co0.5Al alloy maintains the high spin polarization under the effect of B2 disorder.

Enhanced Magnetization in CoFe2O4 Through Hydrogen Doping

AbstractMagnetic spinel oxides have attracted extensive research interest due to their rich physics and wide range of applications. However, these materials invariably suffer suppressed magnetization, due to structural imperfections (e.g., disorder, anti‐site defects, etc.). Herein, a dramatic enhanced magnetization is obtained with an increasement of 5 µB/u.c in CoFe2O4 (CFO) through ionic liquid gating induced hydrogen doping. The intercalated hydrogen ions lead to both distinct lattice expansion of ≈0.7% and notable Fe valence state reduction through electron doping, in which ≈17% Fe3+ is reduced into Fe2+. These facts collectively trigger a site‐specific spin‐flip on tetrahedrally coordinated Co2+ sites that enhances the net ferrimagnetic moment nearly to its theoretical maximum for perfect CFO.

Magnetic order and magnetotransport in half-metallic ferrimagnetic MnyRuxGa thin films

The ruthenium content of half-metallic ${\mathrm{Mn}}_{2}{\mathrm{Ru}}_{x}\mathrm{Ga}$ thin films, with a biaxially strained inverse Heusler structure, controls the ferrimagnetism that determines their magnetic and electronic properties. An extensive study of ${\mathrm{Mn}}_{y}{\mathrm{Ru}}_{x}\mathrm{Ga}$ films on MgO (100) substrates with $1.8\ensuremath{\le}y\ensuremath{\le}2.6$ and $x=0.5, 0.7 \mathrm{or} 0.9$, including crystallographic, magnetic order, magneto-transport, and spin polarization, is undertaken to map specific composition-dependent properties in this versatile ternary system. A comparison of experimental densities obtained from x-ray reflectivity with calculated densities indicates full-site occupancy for all compositions, which implies chemical disorder. All moments lie on a Slater-Pauling plot with slope 1 and all except $x=0.5$, $y=2.2$ exhibit magnetic compensation at ${T}_{\text{comp}}$ below 500 K. The coercivity near ${T}_{\text{comp}}$ exceeds 10 T. Increasing the Mn or Ru content raises ${T}_{\text{comp}}$, but increasing Ru also decreases the spin polarization determined by point contact Andreev reflection. Molecular-field theory is used to model the temperature dependence of the net ferrimagnetic moment and three principal exchange coefficients are deduced. Marked differences in the shape of anomalous Hall and net magnetization hysteresis loops are explained by substantial canting of the small net moment by up to ${40}^{\ensuremath{\circ}}$ relative to the $c$ axis in zero field, which is a result of slight noncollinearity of the ${\mathrm{Mn}}^{4c}$ sublattice moments due to competing intrasublattice exchange interactions arising from antisite disorder and excess Mn in the unit cell. Consequences are reduced-spin polarization and an enhanced intrinsic contribution to the anomalous Hall effect. The systematic investigation of the physical properties as a function of $x$ and $y$ will guide the selection of compositions to meet the requirements for magnonic and spintronic MRG-based devices.

Origin of ferrimagnetism and the effect of octahedral tilting in double-perovskite compound [formula omitted

Density functional theory simulations were used to investigate double-perovskite Sr2CoRuO6 for its structure and magnetic properties. Calculated results show that rocksalt B-site order is stable under all the considered ferromagnetic (FM) and antiferromagnetic (AFM) configurations. Moreover, electronic and magnetic properties are strongly coupled to octahedral tilting. The ground state of rocksalt Sr2CoRuO6 is C type AFM with a0a0c- tilt and a 0.72 eV gap between Ru4d and Co3d orbitals. Possible reason for the presence of ferrimagnetism is attributed to G type AFM with ferrimagnetic moment of 1 μB per formula unit.

X-ray magnetic linear dichroism study of field-manipulated canted antiferromagnetism in epitaxial α−Fe2O3 films

This paper describes manipulation of the antiferromagnetic (AFM) moment by external magnetic field in thin epitaxial nanofilms of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$---the iron oxide polymorph known for its canted antiferromagnetism above the Morin temperature. The field-driven rotation of the AFM moment has been detected in thin $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$/GaN layers by monitoring the azimuthal field dependence of the x-ray magnetic linear dichroism line shape at ${L}_{23}$ absorption edge of iron. The presence of the tiny canted ferrimagnetic (FM) moment in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ makes it possible to manipulate the related AFM moment by applying external magnetic field, monitoring the field-driven rotation of both AFM and FM moments that otherwise can be hardly detected in a nanoscale film by conventional magnetometry. A controllable manipulation of the AFM moment in a thin film by external magnetic field is supposed to be an important keystone for development of the emerging field of AFM spintronics.

Tailoring the electronic structure and magnetic properties of pyrochlore Co2Ti1−x Ge x O4: a GGA + U ab initio study

We report the electronic structure and magnetic properties of Co2Ti1−x Ge x O4 (0 ⩽ x ⩽ 1) spinel by means of the first-principle methods of density functional theory involving generalized gradient approximation along with the on-site Coulomb interaction (U eff) in the exchange-correlation energy functional. Special emphasis has been given to explore the site occupancy of Ge atoms in the spinel lattice by introducing the cationic disorder parameter (y) which is done in such a way that one can tailor the pyrochlore geometry and determine the electronic/magnetic structure quantitatively. For all the compositions (x), the system exhibits weak tetragonal distortion (c/a ≠ 1) due to the non-degenerate and states (e g orbitals) of the B-site Co. We observe large exchange splitting (ΔEX ∼ 9 eV) between the up and down spin bands of t 2g and e g states, respectively, of tetrahedral and octahedral Co2+ (4A2(g)(F)) and moderate crystal-field splitting (ΔCF ∼ 4 eV) and the Jahn–Teller distortion (ΔJT ∼ 0.9 eV). These features indicate the strong intra-atomic interaction which is also responsible for the alteration of energy band-gap (1.7 eV ⩽ E g ⩽ 3.3 eV). The exchange interaction (J BB ∼ −4.8 meV, for (x, y) = (0.25, 0)) between the Co2+ dominates the overall antiferromagnetic behaviour of the system for all ‘x’ as compared to J AA (∼−2.2 meV, for (x, y) = (0.25, 0)) and J AB (∼−1.8 meV, for (x, y) = (0.25, 0)). For all the compositions without any disorderness in the system, the net ferrimagnetic moment (Δμ) remains constant, however, increases progressively with increasing x due to the imbalance of Co spins between the A- and B-sites.

Synthesis and magnetic hyperthermia properties of zwitterionic dopamine sulfonate ligated magnesium ferrite and zinc ferrite nanoparticles

$${\text{MgFe}_{2}\text {O}_{4}}$$ and $$\text {ZnFe}_{2}\text {O}_{4}$$ nanoparticles have shown relatively good biocompatibility and high superparamagnetic hyperthermia value, on par with the well-studied $$\text {Fe}_{3}\text {O}_{4}$$ nanoparticles. However, different studies have reported different values of hyperthermia on both the compounds. To elucidate which compound is superior hyperthermia compound, well-crystallined and narrow size distributed $$\text {MgFe}_{2}\text {O}_{4}$$ and $$Z\text {nFe}_{2}\text {O}_{4}$$ spherical nanoparticles (16 nm diameter) were synthesized by solvothermal reflux method and studied their magnetic hyperthermia values under identical conditions. To further enhance superparamagnetic hyperthermia in $$\text {MgFe}_{2}\text {O}_{4}$$ and $$\text {ZnFe}_{2}\text {O}_{4}$$ nanoparticles, hydrodynamic diameter of nanoparticles were reduced by completely removing the long chain oleic acid surfactant monolayer on nanoparticles and ligated short chain zwitterionic dopamine sulfonate surfactant on bare nanoparticles. These nanoparticles show good aqueous colloidal stability with zeta potential of − 32 mV. The study reveals that $$\text {MgFe}_{2}\text {O}_{4}$$ nanoparticles shows higher hyperthermia value (265 W/g) than that (216 W/g) of $$\text {ZnFe}_{2}\text {O}_{4}$$ nanoparticles at 1 mg/mL concentration under 35.33 kA/m and 316 kHz field parameters. This is high value at 1 mg/mL concentration compared to literature. High hyperthermia value arises from higher saturation mass magnetization (45.5 emu/g) of $$\text {MgFe}_{2}\text {O}_{4}$$ than that (36.5 emu/g) of $$\text {ZnFe}_{2}\text {O}_{4}$$ nanoparticles. High saturation magnetization of $$\text {MgFe}_{2}\text {O}_{4}$$ results from the preferential tetrahedral sites occupation of nonmagnetic $${\text {Mg}^{2+}}$$ due to small ionic radii than $${\text {Zn}^{2+}}$$ ions. If tetrahedral magnetic sublattice is occupied by more nonmagnetic cations, the net ferrimagnetic moment increases. The samples were characterized by X-ray diffraction, infrared spectra, thermogravimetry analysis, differential scanning calorimetry, field emission scanning electron microscope, zeta potential, vibrating sample magnetometer, calorimetric hyperthermia methods.

The existence and origin of field-induced ferrimagnetic order transition of LuFe2O4 single crystal

The magnetic characteristics of LuFe2O4 have been investigated in detail; however, only a few studies have been conducted on the microscopic origins of magnetic field-induced ferrimagnetic transition, and the magnetic coupling between ferrimagnetic domains is still unclear. Especially, because the LuFe2O4 ferrimagnetic transition field is too high for commercial instruments, it is very difficult to directly observe the change in ferrimagnetic domains at lower temperatures by magnetic imaging in real space. In this study, the ferrimagnetic transition was measured using a self-made high field magnetic force microscopy. In addition, magnetization, magnetoelastic, and magnetothermal behavior of the single crystal of LuFe2O4 were investigated. The experimental results show that at lower temperatures (far lower than the ferrimagnetic ordering temperature, TC = 240 K), when the critical field is about ~13.5 T (at 2 K), the ferrimagnetic domain is long-range ordered and stable within the magnetic field below 55 T. The magnetoelastic and magnetothermal effects were observed with field-induced ferrimagnetic transition. The change in the ferrimagnetic moment realignment driven by the magnetic field was proposed, which will lead to the change of ferrimagnetic order, magnetoelasticity, and the multiferroicity behavior.

Ferrimagnetic 120∘magnetic structure inCu2OSO4

We report magnetic properties of a 3d$^9$ (Cu$^{2+}$) magnetic insulator Cu2OSO4 measured on both powder and single crystal. The magnetic atoms of this compound form layers, whose geometry can be described either as a system of chains coupled through dimers or as a Kagom\'e lattice where every 3rd spin is replaced by a dimer. Specific heat and DC-susceptibility show a magnetic transition at 20 K, which is also confirmed by neutron scattering. Magnetic entropy extracted from the specific heat data is consistent with a $S=1/2$ degree of freedom per Cu$^{2+}$, and so is the effective moment extracted from DC-susceptibility. The ground state has been identified by means of neutron diffraction on both powder and single crystal and corresponds to a $\sim120$ degree spin structure in which ferromagnetic intra-dimer alignment results in a net ferrimagnetic moment. No evidence is found for a change in lattice symmetry down to 2 K. Our results suggest that \sample \ represents a new type of model lattice with frustrated interactions where interplay between magnetic order, thermal and quantum fluctuations can be explored.

Polarizing an antiferromagnet by optical engineering of the crystal field

Strain engineering is widely used to manipulate the electronic and magnetic properties of complex materials. An attractive route to control magnetism with strain is provided by the piezomagnetic effect, whereby the staggered spin structure of an antiferromagnet is decompensated by breaking the crystal field symmetry, which induces a ferrimagnetic polarization. Piezomagnetism is especially attractive because unlike magnetostriction it couples strain and magnetization at linear order, and allows for bi-directional control suitable for memory and spintronics applications. However, its use in functional devices has so far been hindered by the slow speed and large uniaxial strains required. Here, we show that the essential features of piezomagnetism can be reproduced with optical phonons alone, which can be driven by light to large amplitudes without changing the volume and hence beyond the elastic limits of the material. We exploit nonlinear, three-phonon mixing to induce the desired crystal field distortions in the antiferromagnet CoF$_2$. Through this effect, we generate a ferrimagnetic moment of 0.2 $\mu_B$ per unit cell, nearly three orders of magnitude larger than achieved with mechanical strain.

Group-theoretical analysis of structural instability, vacancy ordering and magnetic transitions in the system troilite (FeS)-pyrrhotite (Fe1-xS).

A group-theoretical framework to describe vacancy ordering and magnetism in the Fe1-xS system is developed. This framework is used to determine the sequence of crystal structures consistent with the observed magnetic structures of troilite (FeS), and to determine the crystallographic nature of the low-temperature Besnus transition in Fe0.875S. It is concluded that the Besnus transition is a magnetically driven transition characterized by the rotation of the moments out of the crystallographic plane to which they are confined above the transition, accompanied by small atomic displacements that lower the symmetry from monoclinic to triclinic at low temperatures. Based on the phase diagram, magnetically driven phase transitions at low temperatures are predicted in all the commensurate superstructures of pyrrhotite. Based on the phase diagram, magnetically driven spin reorientations at low temperatures are predicted in all the commensurate superstructures of pyrrhotite. The exact nature of the spin rotation is determined by the symmetry of the vacancy-ordered state and based on this spin-flop transitions in 3C and 5C pyrrhotite and a continuous rotation akin to that seen in 4C pyrrhotite are predicted. A Besnus-type transition is also possible in 6C pyrrhotite. Furthermore, it is clarified that 3C and 4C pyrrhotite carry a ferrimagnetic moment whereas 5C and 6C are antiferromagnetic.

The Effect of Pressure on Magnetic Properties of Prussian Blue Analogues

We present the review of pressure effect on the crystal structure and magnetic properties of Cr(CN)6-based Prussian blue analogues (PBs). The lattice volume of the fcc crystal structure space group Fm 3 ¯ m in the Mn-Cr-CN-PBs linearly decreases for p ≤ 1.7 GPa, the change of lattice size levels off at 3.2 GPa, and above 4.2 GPa an amorphous-like structure appears. The crystal structure recovers after removal of pressure as high as 4.5 GPa. The effect of pressure on magnetic properties follows the non-monotonous pressure dependence of the crystal lattice. The amorphous like structure is accompanied with reduction of the Curie temperature (TC) to zero and a corresponding collapse of the ferrimagnetic moment at 10 GPa. The cell volume of Ni-Cr-CN-PBs decreases linearly and is isotropic in the range of 0–3.1 GPa. The Raman spectra can indicate a weak linkage isomerisation induced by pressure. The Curie temperature in Mn2+-CrIII-PBs and Cr2+-CrIII-PBs with dominant antiferromagnetic super-exchange interaction increases with pressure in comparison with decrease of TC in Ni2+-CrIII-PBs and Co2+-CrIII-PBs ferromagnets. TC increases with increasing pressure for ferrimagnetic systems due to the strengthening of magnetic interaction because pressure, which enlarges the monoelectronic overlap integral S and energy gap ∆ between the mixed molecular orbitals. The reduction of bonding angles between magnetic ions connected by the CN group leads to a small decrease of magnetic coupling. Such a reduction can be expected on both compounds with ferromagnetic and ferrimagnetic ordering. In the second case this effect is masked by the increase of coupling caused by the enlarged overlap between magnetic orbitals. In the case of mixed ferro–ferromagnetic systems, pressure affects μ(T) by a different method in Mn2+–N≡C–CrIII subsystem and CrIII–C≡N–Ni2+ subsystem, and as a consequence Tcomp decreases when the pressure is applied. The pressure changes magnetization processes in both systems, but we expect that spontaneous magnetization is not affected in Mn2+-CrIII-PBs, Ni2+-CrIII-PBs, and Co2+-CrIII-PBs. Pressure-induced magnetic hardening is attributed to a change in magneto-crystalline anisotropy induced by pressure. The applied pressure reduces saturated magnetization of Cr2+-CrIII-PBs. The applied pressure p = 0.84 GPa induces high spin–low spin transition of cca 4.5% of high spin Cr2+. The pressure effect on magnetic properties of PBs nano powders and core–shell heterostructures follows tendencies known from bulk parent PBs.

Magnetic properties of ilmenite Mn2FeSbO6

In the work presented the magnetic properties of the high pressure ilmenite phase Mn_2FeSbO_6 are investigated in detail. It is shown that Mn_2FeSbO_6 ilmenite is ferrimagnetic (T_N approximate to 270 K) and exhibits a near-zero coercive field H_C. Furthermore, the Mn^2+-Mn^2+, Fe^3+-Fe^3+ and Mn^2+-Fe^3+ magnetic exchange interactions exhibit gradual and continuous variations with temperature and magnetic field. The ferrimagnetic moment is unsaturated even at 120 kOe below the theoretical value of 5 mu_B per f.u.

Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy

Understanding the transfer of spin angular momentum is essential in modern magnetism research. A model case is the generation of magnons in magnetic insulators by heating an adjacent metal film. Here, we reveal the initial steps of this spin Seebeck effect with <27 fs time resolution using terahertz spectroscopy on bilayers of ferrimagnetic yttrium iron garnet and platinum. Upon exciting the metal with an infrared laser pulse, a spin Seebeck current js arises on the same ~100 fs time scale on which the metal electrons thermalize. This observation highlights that efficient spin transfer critically relies on carrier multiplication and is driven by conduction electrons scattering off the metal–insulator interface. Analytical modeling shows that the electrons’ dynamics are almost instantaneously imprinted onto js because their spins have a correlation time of only ~4 fs and deflect the ferrimagnetic moments without inertia. Applications in material characterization, interface probing, spin-noise spectroscopy and terahertz spin pumping emerge.

Structural, magnetic and dielectric properties of the novel magnetic spinel compounds ZnCoSnO4 and ZnCoTiO4

The transparent semiconductor Zn2SnO4 with cubic spinel structure and the isostructural Zn2TiO4 have been magnetically doped with Co2+. ZnCoSnO4 and ZnCoTiO4 exhibit ferrimagnetism below TN ≈ 13 K and TN ≈ 17 K. Ferrimagnetic moments are evident in M vs H curves below TN by small hysteresis. Fits to strictly linear Curie-Weiss plots above TN give μeff ≈ 4.86 μB and ≈4.91 μB for ZnCoSnO4 and ZnCoTiO4, above theoretical predictions. Impedance spectroscopy data from sintered ceramic can be fitted with a standard equivalent circuit model based on two RC elements for bulk and GB areas. The relative dielectric permittivity of the bulk is ≈20 and ≈30 for Zn2SnO4 and Zn2TiO4. The semiconducting ZnCoSnO4 and ZnCoTiO4ceramics exhibit bulk resistivity of ≈1 106 Ω cm and ≈1 105 Ω cm at 560 K (287 °C), and bulk activation energies of EA ≈ 1.2 eV and 1.1 eV.

Magnetic and Electrical Properties of Spinel Copper Ferrite Thin Films

Copper ferrite (CuSUBx/SUBFeSUB3-x/SUBO₄) thin films synthesized on α-Al₂O₃(0001) substrates exhibited the spinel structure for Cu compositions up to x = 1.0. The substituent Cu ions exhibited charge valence of +2, occupying both the tetrahedral and the octahedral sites of the spinel lattice. Magnetic hysteresis measurements on the CuSUBx/SUBFeSUB3-x/SUBO₄ films revealed gradual loss of saturation magnetization (MSUBs/SUB) with increasing x: MSUBs/SUB is reduced to ~50% that of Fe₃O₄ for x = 1.0. The electrical resistivity (ρ) of the CuSUBx/SUBFeSUB3-x/SUBO₄ films increased with x: ρ for x = 1.0 is larger by a factor of 30 than that of Fe₃O₄. The evolution of the magnetic and electrical properties of CuSUBx/SUBFeSUB3-x/SUBO₄ can be explained in terms of the competition between the tetrahedral and octahedral CuSUP2+/SUP density for ferrimagnetic moment and polaronic conduction.

Stability of cluster glass state in nano order sized YbFe2O4 powders

Slow magnetic relaxation and the Fe ion stoichiometry were investigated in spin and charge frustrated system YbFe2O4. DC susceptibility, AC susceptibility, aging process and electron diffraction observation were carried out on nano order sized YbFe2O4 single-phase powders with the Fe/Yb=2.00, 2.02, and 2.04 ratios. The variation of the cluster glass behavior was studied in relation between the magnetic relaxation and the various chemical compositions. With the increase of the Fe/Yb ratios, the magnetic coherence length increased and the magnetic aging time goes slow down. The observed critical slowing down of the glassy fluctuation is interpreted by the development of the spin cluster size. This indicates that the spin glass like property of this material arises from the competition between various sized magnetic domains having ferrimagnetic moments. Additionally, electron diffraction experiments showed that the increase of Fe/Yb ratios from Fe/Yb=2.00 enhances the development of the charge ordering coherence in triangular lattice. This study shows that the measurement of magnetic fluctuation for nano order sized particles gives the essential information about the spin cluster fluctuation in RFe2O4.

Magnetic Transitions in Chemically Synthesized Nanoparticles of CoCr2O4

Bulk CoCr2O4 undergoes a transition from paramagnetic to long-range ferrimagnetic phase at $T_{c}$ (94 K) to a long-range and/or short-range spiral order at $T_{s}$ ( $\sim 24$ K), and finally shows a lock-in-transition below 15 K. The spiral component induces an electric polarization and also a spontaneous magnetization for which it is said to be multiferroic. Reducing the size of a CoCr2O4 multiferroic material to $\sim 50$ nm by a coprecipitation method, we obtain a pure cubic phase with space group, Fd3m and lattice parameter (8.334 ± 0.003 °A). A rich sequence of magnetic transitions are examined by measuring temperature and field-dependent magnetization and diffused neutron scattering (DNS) using polarized neutron at different temperatures. While paramagnetic to ferrimagnetic transition is enhanced from 97 K in bulk to 99 K at 0.5 kOe field, followed by a decrease in lock-in-transition ( $T_{L}$ ) from 15 K in bulk to 8 K, spiral ordering temperature does not show a significant change. A strong disagreement between paramagnetic moment obtained from the fitting of $\chi ^{-1}=({T}/{C})+({1}/{\chi _{o}})-({b}/{T-\theta })$ and ferrimagnetic moment obtained from the $M$ versus $H$ loop taken at 2 K, nonsaturated magnetization at 50–100 kOe field, two order of magnitude higher coercivity ( $H_{c}$ ), and splitting of ac susceptibly confirm the core–shell structure of the particles. Furthermore, a magnetic scattering analysis clearly shows that while the paramagnetic to ferrimagnetic transition is continuous, the spiral ordering is sharp, short range, and commensurate in contrast to incommensurate spiral order observed single crystal of CoCr2O4.

Two-dimensional charge disproportionation of the unusual high valence state Fe(4+) in a layered double perovskite.

The crystal and magnetic structures of charge-disproportionated Ca2FeMnO6 were analyzed by neutron powder diffraction. Ca2FeMnO6 is a layered double perovskite oxide with a two-dimensional arrangement of Mn(4+) and unusual high valence Fe(4+) at room temperature. When cooled, the compound shows charge disproportionation followed by magnetic transition. Around 200 K, the Fe(4+) shows the charge disproportionation to Fe(3+) and Fe(5+), which are ordered in a checkerboard pattern in the two-dimensional FeO6 octahedral layers. The magnetic transition occurs at 95 K, which is much lower than the charge disproportionation temperature. The magnetic structure is commensurate but noncollinear, and the antiferromagnetic coupling of Fe(3+) and Fe(5+) spins in the FeO6 octahedral layers gives the ferrimagnetic moments. The unique magnetic structure is described as a result of two-dimensional localization of the ligand holes with effective spins.

Site-specific electronic structures of ferrimagnetic Fe3O4 measured by resonant X-ray magnetic scattering

Resonant magnetic scattering of circularly polarized synchrotron X-rays has revealed the site-specific magnetic moments at two non-equivalent Fe ion sites in Fe3O4. The energy-dependent peaks for the 026 and 266 reflections were attributed ferrimagnetically to the e and t 2 energy levels of Fe 3d at the A site, and to the t 2g and e g levels at the B site, respectively, having a sequence of t 2g, e, e g and t 2 in order of energy. This sequence agrees with the local spin-density approximation calculations in the literature [Anisimov, Elfimov, Hamada &amp; Terakura, (1996). Phys. Rev. 54, 4387–4390], in which the spin-down band at the Fermi energy corresponds to t 2g . Resonant magnetic Fourier synthesis reveals the electron densities of the ferrimagnetic moments.