Spin-polarized Electron Momentum Research Articles

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.

ChemInform Abstract: Magnetic Compton Scattering: A Reliable Probe to Investigate Magnetic Properties

AbstractReview: 8 refs.

Competition of 3d/4f orbitals due to competing conductivity and ferromagnetism in Fe/CoAs layers in Eu(Fe0.89Co0.11)2As2

The spin-polarized electron momentum density along the [100] direction of Eu(Fe0.89Co0.11)2As2 was measured using Magnetic Compton Scattering (MCS). Measurements were performed at different temperatures and applied external magnetic fields. These results provide the first direct insight into the orbital interactions that are responsible for the competing conductivity and ferromagnetism (FM) in this iron pnictide system. The orbital-wise decompositions of the density distribution show that at low applied magnetic field (0.1 T), the spin-polarized average Fe/Co-3d character is enhanced between 15 K and 19 K with a maximum at 17 K, the temperature at which the resistivity shows a local maximum, followed by re-entrant SC (superconducting)-like character. This clearly shows the dominance of the ferromagnetic character over conducting character in this temperature region where the resistivity shows a maximum. At higher applied magnetic field, we do not see this enhancement and subsequent collapse of the Fe/Co-3d character as the temperature decreases, consistent with the disappearance of the re-entrant SC-like feature at higher applied magnetic field. These data support a model in which the spin-polarization of the Fe/Co-3d orbitals is enhanced by the ferromagnetic Eu-ions, leading to the suppression of conductivity at ∼17 K (for 0.1 T), while at lower temperature the conductivity recovers and the Fe/Co-3d spin-polarization collapses.

Spin-polarized itinerant electrons in Co-based Heusler compounds investigated by magnetic Compton scattering

The spin-polarized electron momentum density distributions (magnetic Compton profiles) of Co2YAl (Y = Ti, V, Cr, and Fe) Heusler compounds have been measured using a magnetic Compton scattering technique. The experimental magnetic Compton profiles have been decomposed into the itinerant electron and localized 3d electron contributions. The decomposition shows that the number of spin-polarized itinerant electrons is proportional to that of spin-polarized localized 3d electrons, indicating that the strength of indirect exchange interaction is dominated by the localized 3d magnetic moment. This finding suggests that the spin-polarized itinerant part in the magnetic Compton profile is used as a scale that can measure the strength of the sp-d interaction.

Imaging of 3dMn orbitals in the ferromagnetic state for Ca-substituted manganite: Magnetic Compton investigation

The 3$d$ Mn orbitals in Pr${}_{0.25}$Ca${}_{0.25}$MnO${}_{3}$ (PCMO), in the ferromagnetic phase, were imaged by two-dimensional reconstruction of spin-polarized electron-momentum density projected along the [100] and [110] principal directions. The results were analyzed using a molecular-orbital scheme to understand the population distribution for the ${t}_{2g}$ and the ${e}_{g}$ states for Mn. The analysis shows that the ${t}_{2g}$ states are found to be half-filled, whereas, the ${e}_{g}$ states are dominated mainly by ${x}^{2}\ensuremath{-}{z}^{2}$-type orbitals for both projected [100] and [110] principal directions. The observance of preferential filling of the ${x}^{2}\ensuremath{-}{z}^{2}$-orbital type is consistent with a cooperative Jahn-Teller distortion of the MnO${}_{6}$ octahedra leading to a local tetragonal compression along the $y$ axis for this system. As a result of this distortion, the 3${y}^{2}\ensuremath{-}{r}^{2}$-type orbitals have a small population for PCMO; the ratio of the ${x}^{2}\ensuremath{-}{z}^{2}$-type orbitals to that of the 3${y}^{2}\ensuremath{-}{r}^{2}$-type orbitals is greater than 2, similar to that seen for bilayered manganites.

Temperature and field dependent magnetic Compton scattering study of Heusler alloy Co2MnSi

Temperature and field dependent spin polarized electron momentum distributions in ternary Heusler compound Co2MnSi have been measured using the magnetic Compton spectrometer at SPring-8, Japan. The experimental magnetic Compton profile at 10 K reconciles well with the theoretical profile computed using the spin polarized relativistic (SPR) Korringa–Kohn–Rostoker (KKR) method. The temperature and field dependent experimental magnetic profiles have been mainly analyzed to check the role of Mn 3d electrons in the formation of magnetic moments in Co2MnSi. The diffuse contribution from conduction electrons is antiferromagnetically coupled to the spin moment arising from 3d electrons of Co and Mn. The spin moments calculated using SPR-KKR calculations are in good agreement with the present measurements.

Competing Ferromagnetism and Superconductivity on FeAs Layers inEuFe2(As0.73P0.27)2

We have measured the spin-polarized electron momentum density distributions of EuFe2(As0.73P0.27)2 by magnetic Compton scattering (MCS) measurements. For the first time, we show direct evidence of competing ferromagnetism and superconductivity (SC) on FeAs layers in this iron pnictide system. The MCS orbitalwise decomposition of the density distributions reveals that between 16 and 19 K, the spin-polarized Fe-3d character is enhanced (as the ferromagnetic character supersedes superconducting character), where the resistivity shows a maximum, reentrant SC-like peak, at 18 K. The spin polarization of the Fe-3d orbital, enhanced by ferromagnetic Eu ions, suppresses the SC around 18 K, while at other temperatures the system indeed exhibits SC where the Fe-3d spin polarization is suppressed or collapses.

Direct observation of the magnetic spin component of samarium–iron-based laves compound by magnetic Compton scattering

The spin-polarized electron momentum distributions (magnetic Compton profiles: MCP's) of SmFe 1.86Al 0.14 along the [1 1 1] direction have been measured at 10 and 300 K using the magnetic Compton scattering technique. It is found that the orbital moment dominates the magnetization in this compound. A comparison with a theoretical profile support that the shape of the experimental MCP's is reproduced by a sum of positive Fe and negative Sm 4f spin components. A slight difference is observed in the shape of MCP between 10 and 300 K.

Spin-polarized electron momentum density in [formula omitted

The spin-polarized electron momentum density (EMD) of single-crystal ferromagnetic GdRh 3 B 2 has been probed by the magnetic Compton scattering technique. The spin moment is determined to be 6.83 ± 0.43 μ B per formula unit and the one-dimensional projection of the spin-polarized EMD (magnetic Compton profile) is obtained along the [ 1 0 1 ¯ 0 ] direction. These results are in good agreement with those predicted by a first-principles band structure computation with the spin–orbit interactions.

Spin-resolved Compton scattering study ofRuSr2GdCu2O8

The spin-polarized electron momentum distributions of the magnetic superconductorRuSr2GdCu2O8 in its various phases have been measured using the magnetic Compton scattering techniquewith elliptically polarized synchrotron radiation. A contribution to the spin moment frommagnetically ordered Ru 4d electrons was seen with a large induced Gd 4f moment below25 K. A small negatively polarized component is observed in the antiferromagnetic phase ofthe Gd sublattice, at 2 K. The momentum distribution of this was consistent with theexistence of a Gd 5d electron moment anti-parallel with respect to the now ordered Gd 4fmoment.

A magnetic Compton scattering study of double perovskiteSr2FeMoO6

The spin-polarized electron momentum distribution (magnetic Compton profile: MCP) of ferromagneticSr2FeMoO6 has been measured using the magnetic Compton scattering technique at room temperature.The experimental MCP is in good agreement with that obtained by a first-principlesband-structure calculation. The experiment and calculation reveal a hollow aroundpz = 0, which support the conclusion that there exists a negatively spin-polarized Fe 3d–Mo 4dmixed state.

Evidence of negative spin polarization in ferromagneticSr2FeMoO6as observed in a magnetic Compton profile study

The spin-polarized electron momentum distribution [magnetic Compton profile (MCP)] of ferromagnetic ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ has been measured, using the magnetic Compton scattering technique, at temperatures $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, for the [100] and [110] crystallographic directions. The experimental results have been compared with results from electronic structure calculations performed utilizing the full potential linearized augmented plane-wave method. The calculated results clearly show that only down-spin states contribute to the ${E}_{\mathrm{F}}$ intensity (half metallic character). The experimental observations clearly show evidence for the existence of negative spin polarization that arises from down-spin bands. We have observed the change in the MCP, which arises from the band spin fluctuation, between the low temperature $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and high temperature $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Magnetic Compton scattering study of CeRh3B2

The spin-polarized electron momentum distribution(magnetic Compton profile: MCP) of ferromagnetic CeRh3B2has been measured using the magnetic Compton scattering technique at 10 K for the[112̄0]direction. In this compound, the orbital moment dominates themagnetization. An analysis of the MCP reveals that the Ce 4f andCe 5d spin moments are aligned parallel with a value of −0.68 ± 0.08 and 0.41 ± 0.04μB,respectively, while Rh 4d electrons do not carry any significant spin moment.The ratio of orbital to spin moments for Ce 4f electrons, which has beendetermined from comparison of the present data with recent polarizedneutron diffraction data, is rather smaller than that for Ce3+ions. This result implies strong hybridization of the Ce 4f orbital with the orbitalson the surrounding ions.

Magnetic Compton scattering study of colossal magnetoresistance materialsFe1−xCuxCr2S4

The spin-polarized electron momentum distributions in the Cr-based chalcogenide spinels ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{Cr}}_{2}{\mathrm{S}}_{4}$ $(x=0.0,0.5,1.0)$ have been measured using a magnetic Compton scattering technique at $T=10\mathrm{K}.$ The experimental magnetic Compton profiles have been compared with the results from electronic structure calculations performed using the full potential linearized augmented plane-wave method. The theoretical analysis includes a decomposition of the various orbital and atomic contributions. For $x=0.0$ and 0.5 sample compositions, the results show that the magnetic moments of the tetrahedrally coordinated ${\mathrm{Fe}}^{2+}$ (for $x=0.0)$ and ${\mathrm{Fe}}^{3+}$ (for $x=0.5)$ with spin moments of $3.66{\ensuremath{\mu}}_{B}$ (for $x=0.0)$ per formula unit $({\mathrm{FU}}^{\ensuremath{-}1})$ and $1.6{\ensuremath{\mu}}_{B}$ ${\mathrm{FU}}^{\ensuremath{-}1}$ (for $x=0.5),$ are aligned antiparallel to those of the octahedrally coordinated ${\mathrm{Cr}}^{3+}$ with spin moments of $5.0{\ensuremath{\mu}}_{B}$ ${\mathrm{FU}}^{\ensuremath{-}1}$ (for $x=0.0)$ and $4.82{\ensuremath{\mu}}_{B}$ ${\mathrm{FU}}^{\ensuremath{-}1}$ (for $x=0.5).$ In the ferromagnetic system for $x=1.0,$ the Cr moment is found to be $5.28{\ensuremath{\mu}}_{B}$ ${\mathrm{FU}}^{\ensuremath{-}1}.$

Spin-polarized electron momentum density distributions in the Invar systemFe3Pt

The one-dimensional projections of the spin polarized electron momentum distributions of ${\mathrm{Fe}}_{3}\mathrm{Pt}$ have been measured, using the magnetic Compton scattering technique, in the temperature range 15--500 K, for the 110 and 111 crystallographic directions in the chemically ordered and disordered phases. The experimental data have been compared with results from electronic structure calculations performed using the linearized muffin-tin-orbital and full potential linearized augmented plane-wave methods and the single-site Green's-function Korringa-Kohn-Rostoker method for the ordered and disordered samples, respectively. The projection of the spin moment momentum distribution as a function of temperature remains characteristic of a Fe $3d$ moment until well above ${T}_{c}.$ No evidence of an indicative change in profile shape is observed that would suggest a redistribution of charge from ${e}_{g}$ to ${t}_{2g}$ orbitals in the Fe band structure that would, in turn, support the Weiss two-state model for the Invar effect.

Spin-polarized electron momentum density distributions [formula omitted

The spin-polarized electron momentum distributions (EMD) for ferrimagnetic GdMn 2Ge 2 and ferromagnetic LaMn 2Ge 2 have been measured using the magnetic Compton scattering technique. The spin-polarized EMDs were resolved along the c-axis at 15 K . In the Gd sample, the Gd and Mn spin sublattices are aligned antiparallel with spin moments of 6.8±0.1 μ B per formula unit (FU −1) and 3.7±0.1μ B FU −1 , respectively, with the Gd spin sublattice oriented parallel to the scattering vector. The ferromagnetic La system exhibits no 4f moment and the Mn moment is aligned parallel to the scattering vector, the ordered spin moment on the Mn being 2.4±0.1μ B FU −1 . The two samples measured are the extreme points of the phase diagram for Gd 1− x La x Mn 2Ge 2. Our data give a direct indication of the sublattice reorientation at x≈0.5, implied from previous magnetization measurements and indicate that at a low temperature the Mn sublattice is a canted ferromagnetic system.