Ratio Of Magnetic Moments Research Articles

X-ray magnetic circular dichroism investigation of electric field manipulation of magnetization reversal in Ta/CoFeB/(011)PMN-PT heterostructure

A tunable and nonvolatile magnetoelectric coupling effect and magnetization reversal in demagnetized Ta/CoFeB/(011)PMN-PT was obtained by applying electric fields without an external magnetic field. X-ray magnetic circular dichroism investigation under an in situ electric field indicates that the orbital magnetic moment to spin magnetic moment ratios of both Fe and Co are enhanced under the electric field. The ratio of Fe under negative electric field control is much larger than that under a positive electric field, while it remains almost unchanged for Co under different electric fields.

Effect of Nb substitution on magneto-optical properties of Co0.5Mn0.5Fe2O4 nanoparticles

This paper focused on the structure, optic and magnetic properties of niobium substituted Co0.5Mn0.5NbxFe2-xO4nanoparticles (NPs) that synthesized by hydrothermal method. The synthesis of cubic spinel ferrite structures was confirmed via XRD, SEM along with EDX and elemental mapping, TEM and FT-IR. The crystallite size of the products was found between 17 and 18 nm. The %DR-UV-visible spectrophotometer revealed that the band gap values are 0.37, 0.52, 0.54, and 0.46 eV for each substitution respectively. Room temperature (RT) and 10 K magnetization measurements were performed on spinel Co0.5Mn0.5Fe2-xNbxO4 (0.00 ≤ x ≤ 0.10) NPs by VSM. The specific magnetic parameters such as saturation magnetization (Ms), remanence (Mr), coercivity (Hc), magnetic moment (nB) and squareness ratio (SQR = Mr/Ms) were determined and evaluated. The M(H) curves showed ferrimagnetic nature at RT and 10 K. The Nb3+ion substitution significantly improves the magnetizations data. An enhancement in the Ms, Mr, and nB values was observed in substituted products compared to pristine one. The highest values were obtained for x = 0.04 product. The obtained magnetic data are primarily derived from the substitution of Fe3+ ions with Nb3+ ions that will strengthen the super-exchange interactions.

Hyperfine Anomalies in Gd and Nd

The hyperfine anomalies in Gd and Nd have been extracted from experimental hyperfine structure constants. In addition to the values of the hyperfine anomaly, new improved values of the nuclear magnetic dipole moment ratios are derived.

High precision measurement of muonium hyperfine structure

MuSEUM (Muonium Spectroscopy Experiment Using Microwave) collaboration aims to measure the muonium hyperfine structure (MuHFS,vhfs) with a few ppb (parts per billion). MuHFS spectroscopy is a stringent test of the bound-state QED. From this measurement, the muon-proton magnetic moment ratio (μμ/μP) and the muon-electron mass ratio (mμ/me) can also be determined by applying a high magnetic field. In the previous MuHFS measurement carried out at Los Alamos Meson Physics Facility (LAMPF), the main uncertainty was caused by the lack of the statistics. MuSEUM collaboration uses the high intense pulsed muon beam at Japan Proton Accelerator Research Complex (J-PARC) to improve the statistical uncertainty. We are also developing our own experimental setups for the improvement of the systematic uncertainties. From June 2016, MuSEUM collaboration have carried out the MuHFS measurement in an extremely low magnetic field within 100 nT and now we are preparing for the measurement in a 1.7 T high magnetic field.

Tuning magnetic coercivity with external pressure in iron-rhenium based ferrimagnetic double perovskites

We studied the effect of physical pressure on the electronic and magnetic properties of ferrimagnetic double perovskites ${A}_{2}{\mathrm{FeReO}}_{6}$ ($A=\mathrm{Ca}$, Ba) using Re ${L}_{2,3}$ edge x-ray absorption spectroscopy and powder diffraction measurements. Volume compression is shown to dramatically increase the magnetic coercivity (${H}_{c}$) in polycrystalline samples of both compounds with $\mathrm{\ensuremath{\Delta}}{H}_{c}/\mathrm{\ensuremath{\Delta}}V\ensuremath{\sim}150$--200 $\mathrm{Oe}/{\AA{}}^{3}$. A nearly eight-fold increase in ${H}_{c}$, from 0.2 to 1.55 T, is obtained in ${\mathrm{Ba}}_{2}{\mathrm{FeReO}}_{6}$ at $P=29$ GPa. While no signs of structural phase transitions are seen in either sample to $\ensuremath{\sim}30$ GPa, the structural data points to a pressure-driven increase in tetragonal distortion of ${\mathrm{ReO}}_{6}$ octahedra. A sizable but pressure-independent Re orbital-to-spin magnetic moment ratio is observed, pointing to the critical role of spin-orbit interactions at Re sites. We present a ${j}_{\mathrm{eff}}$ description of the electronic structure that combines effects of crystal field and spin-orbit coupling on the Re $5{d}^{2}$ orbitals and use this description to provide insight into the pressure-induced enhancement of magnetic anisotropy.

Complex magnetic order in nickelate slabs

Magnetic ordering phenomena have a profound influence on the macroscopic properties of correlated-electron materials, but their realistic prediction remains a formidable challenge. An archetypical example is the ternary nickel oxide system RNiO3 (R = rare earth), where the period-four magnetic order with proposals of collinear and non-collinear structures and the amplitude of magnetic moments on different Ni sublattices have been subjects of debate for decades. Here we introduce an elementary model system - NdNiO3 slabs embedded in a non-magnetic NdGaO3 matrix - and use polarized resonant x-ray scattering (RXS) to show that both collinear and non-collinear magnetic structures can be realized, depending on the slab thickness. The crossover between both spin structures is correctly predicted by density functional theory and can be qualitatively understood in a low-energy spin model. We further demonstrate that the amplitude ratio of magnetic moments in neighboring NiO6 octahedra can be accurately determined by RXS in combination with a correlated double cluster model. Targeted synthesis of model systems with controlled thickness and synergistic application of polarized RXS and ab-initio theory thus provide new perspectives for research on complex magnetism, in analogy to two-dimensional materials created by exfoliation.

Ab-initio study of X-ray absorption and X-ray magnetic circular dichroism spectra of [formula omitted]PtGa and [formula omitted]PtGa alloys

Using first-principles calculations based on density functional theory, we have studied the X-ray absorption spectra (XAS) and X-ray Magnetic Circular Dichroism (XMCD) spectra of Co2PtGa and Mn2PtGa alloys. Using relativistic calculations, we have estimated and analyzed the contribution of the orbital and spin moments to the total magnetic moment for the transition metal atoms, Pt, Co and Mn. It has been observed that while the ratio of orbital and spin magnetic moments of Pt atom in Co2PtGa in cubic phase is substantial, this is an order of magnitude lower in Mn2PtGa. On the other hand, this difference reduces drastically in case of the martensite phase. This signifies the crucial role of the neighborhood in determining the magnetic properties of these materials. Further, the XAS and XMCD spectra at the L2,3 edges of different constituent atoms in various materials have been analyzed. The results (peaks and shoulders present in these XAS and XMCD spectra) have been corroborated with the atom-projected unoccupied density of states of the respective materials.

Spin Polarization of an Ensemble of Alkali Atoms with Zero Average Magnetization

The Lande factors of hyperfine sublevels belonging to the same spectral term differ from each other. This leads to the appearance of an effective gyromagnetic ratio for an atomic ensemble, which can be defined as the ratio of the average magnetic moment to the average angular momentum. Characteristically, this quantity is not a constant, but rather depends on the populations of the hyperfine sublevels. States of an ensemble of atoms occupying their ground level in which the effective gyromagnetic ratio is zero are of much interest. Here, one of such states is considered by the example of alkali metal 87Rb. The main idea is to suggest a method for preparing states with zero effective gyromagnetic ratio by means of two-frequency pumping of a saturated alkali-metal vapor in a cell containing a buffer gas. It is noteworthy that, according to calculations, correlation between the two fields is not required for attaining this goal.

Modeling of magnetic particle orientation in magnetic powder injection molding

The magnetic micro powder orientation under viscous shear flow has been analytically understood and characterized into a new analytical orientation model for a powder injection molding process. The effects of hydrodynamic force from the viscous flow, external magnetic force and internal dipole–dipole interaction were considered to predict the orientation under given process conditions. Comparative studies with a finite element method proved the calculation validity with a partial differential form of the model. The angular motion, agglomeration and magnetic chain formation have been simulated, which shows that the effect of dipole–dipole interaction among powders on the orientation state becomes negligible at a high Mason number condition and at a low λ condition (the ratio of external magnetic field strength and internal magnetic moment of powder). Our developed model can be very usefully employed in the process analysis and design of magnetic powder injection molding.

Interface-induced perpendicular magnetic anisotropy of Co nanoparticles on single-layer h-BN/Pt(111)

Ferromagnetism with perpendicular magnetic anisotropy (PMA) was observed at room temperature in cobalt nanoparticles (NPs) grown on hexagonal boron nitride (h-BN) on a Pt(111) surface. It was shown that the Co NPs have planar hexagonal shapes with a mean diameter of ∼20 nm and a mean height of ∼1.6 nm. The depth-resolved analysis of X-ray magnetic circular dichroism at the Co L2,3-edges revealed that in the ferromagnetic Co NPs, the ratio of the orbital magnetic moment to the spin magnetic moment in the out-of-plane direction becomes larger at the Co NP/h-BN interface than the ratio in bulk Co. The B and N K-edge near edge X-ray absorption fine structures showed the orbital hybridization between the π orbitals of h-BN and d orbitals of Co at the interface, as an origin of the orbital magnetic moment enhancement possibly giving rise to PMA in the Co NPs.

Magnetic characteristics measurements of ethanol–water mixtures using a hybrid-type high-temperature superconducting quantum-interference device magnetometer

The magnetic characteristics of ethanol–water mixtures were investigated using our newly developed hybrid-type magnetometer based on a high-temperature superconducting quantum-interference device. The magnetization (M-H) curves of ethanol–water mixtures show good diamagnetic characteristics. The magnetic moments of the mixture show ethanol concentration dependence. However, the variation in magnetic moment differs from the characteristics expected by considering the magnetic moment ratio between water and ethanol, and volume-reduction rate. It showed two decrement regions separated at approximately 50–60% concentration values. It is also observed that the concentration dependence of the magnetic moment measured using the sample vibration method under a uniform magnetic field and that by the sample rotation method showed slightly different characteristics. These anomalies are attributed to the formation of clustered structures in the mixture.

Correlation between structural order parameter of epitaxial Fe/Pt multilayer and corresponding perpendicular magnetic anisotropy and orbital magnetic moment upon annealing

A strong correlation has been noted between the structural order parameter of an epitaxial L10 Fe/Pt thin film and the corresponding perpendicular magnetic anisotropy (PMA) and orbital magnetic moment. This relationship is studied in detail here. An epitaxial L10 FePt thin film grown from an [Fe(10 Å)/Pt(10 Å)]15 multilayer with (001) orientation was prepared using ion beam sputtering deposition. The Fe/Pt multilayer was transformed into L10 alloy at an annealing temperature of about 500 °C. When annealed at 700 °C, the out-of-plane order parameter of L10 FePt reached 0.95, with the squareness close to 1 and the magnetocrystalline anisotropy constant reaching 3 × 107 erg/cm3. This indicates that the ordered FePt film has a strong PMA effect. The plane-normal orbital-to-spin magnetic moment ratios are 0.088, 0.149 and 0.174 for the samples of Fe/Pt multilayer without annealing, after annealing at 500 °C and the ordered FePt film after 700 °C annealing, respectively. The results suggest that the higher order parameter results in a stronger hybridization and spin–orbital coupling between Fe and Pt atoms. Also, the higher orbital magnetic moment anisotropy implies that the plane-normal orbital-to-spin magnetic moment ratio increases.

Electronic and magnetic properties of TTF and TCNQ covered Co thin films

Interfacial effects like orbital hybridization and charge transfer strongly influence the transfer of spins from ferromagnetic metals to organic semiconductors and can lead to the formation of interfacial states with distinct magnetic properties. The changes in the electronic and magnetic properties of a thin Co film upon adsorption of a layer of either the molecular organic electron donor tetrathiafulvalene (TTF) or the acceptor tetracyanoquinodimethane (TCNQ) have been investigated by X-ray absorption spectroscopy and X-ray magnetic circular dichroism using synchrotron radiation. Clear differences between the spectra of the adsorbed molecules and the neutral molecules show the hybridization of the molecular orbitals with the Co interface. Deposition of both organic materials leads to a small increase of the ratio of the orbital magnetic moment to the spin magnetic moment of the Co atoms at the interface. The main effect of overlayer deposition is a modification of the magnetic hysteresis of the Co film: The TCNQ slightly reduces the coercivity of the Co, while the TTF increases the coercivity by a factor of ∼1.5. These complementary effects of either a molecular organic electron donor or acceptor on the interfacial properties of a metal ferromagnetic thin film are a promising result for the controlled modification of the magnetic structure of hybrid interfaces.

Ensemble magnetic behavior of interacting CoFe nanoparticles

Ferromagnetic nanoparticles in the 10-14 nm size range are examined for their size and interaction dependent magnetic properties. From X-ray magnetic circular dichroism the orbital-to-spin magnetic moment ratio is determined and found to decrease significantly with particle size. This is in accordance with previous complementary studies on smaller particles and highlights the difficulty of fitting to a simple core-shell model. Vibrating sample magnetometry experiments on samples with more than 1000 particles per square micron show a wide distribution of blocking temperatures from 50 to greater than 650 K. This is attributed to the dipole-dipole magnetic coupling forces between particles. The blocking temperatures show an unexpected negative correlation with increasing particle density.

A measurement of the neutron to 199Hg magnetic moment ratio

The neutron gyromagnetic ratio has been measured relative to that of the 199Hg atom with an uncertainty of 0.8 ppm. We employed an apparatus where ultracold neutrons and mercury atoms are stored in the same volume and report the result γn/γHg=3.8424574(30).

On measurement of the isotropy of the speed of light

Three experimental concepts investigating possible anisotropy of the speed of light are presented. They are based on i) beam deflection in a 180° magnetic arc, ii) narrow resonance production in an electron-positron collider, and iii) the ratio of magnetic moments of an electron and a positron moving in opposite directions.

Low-mass right-handed sneutrino dark matter: SuperCDMS and LUX constraints and the Galactic Centre gamma-ray excess

Recent results from direct and indirect searches for dark matter (DM) have motivated the study of particle physics models that can provide weakly interacting massive particles (WIMPs) in the mass range 1–50 GeV. Viable candidates for light WIMP DM must fulfil stringent constraints. On the one hand, the observation at the LHC of a Higgs boson with Standard Model properties set an upper bound on the coupling of light DM particles to the Higgs, thereby making it difficult to reproduce the correct relic abundance. On the other hand, the recent results from direct searches in the CDMSlite, SuperCDMS and LUX experiments have set upper constraints on the DM scattering cross section. In this paper, we investigate the viability of light right-handed sneutrino DM in the Next-to-Minimal Supersymmetric Model (NMSSM) in the light of these constraints. To this aim, we have carried out a scan in the NMSSM parameter space, imposing experimental bounds on the Higgs sector and low-energy observables, such as the muon anomalous magnetic moment and branching ratios of rare decays. We demonstrate that the enlarged Higgs sector of the NMSSM, together with the flexibility provided by the RH sneutrino parameters, make it possible to obtain viable RH sneutrino DM with a mass as light as 2 GeV. We have also considered the upper bounds on the annihilation cross section from Fermi LAT data on dwarf spheroidal galaxies, and extracted specific examples with mass in the range 8–50 GeV that could account for the apparent low-energy excess in the gamma-ray emission at the Galactic Centre. Then, we have computed the theoretical predictions for the elastic scattering cross-section of RH sneutrinos. Finally, after imposing the recent bounds from SuperCDMS and LUX, we have found a wide area of the parameter space that could be probed by future low-threshold direct detection experiments.

Orbital magnetic moment and coercivity ofSiO2-coated FePt nanoparticles studied by x-ray magnetic circular dichroism

We have investigated the spin and orbital magnetic moments of Fe in FePt nanoparticles in the $L$1$_{0}$-ordered phase coated with SiO$_{2}$ by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Fe $L_{\rm 2,3}$ absorption edges. Using XMCD sum rules, we evaluated the ratio of the orbital magnetic moment ($M_{\rm orb}$) to the spin magnetic moment ($M_{\rm spin}$) of Fe to be $M_{\rm orb}/M_{\rm spin}$ = 0.08. This $M_{\rm orb}/M_{\rm spin}$ value is comparable to the value (0.09) obtained for FePt nanoparticles prepared by gas phase condensation, and is larger than the values ($\sim$0.05) obtained for FePt thin films, indicating a high degree of $L$1$_{0}$ order. The hysteretic behavior of the FePt component of the magnetization was measured by XMCD. The magnetic coercivity ($H_{\rm c}$) was found to be as large as 1.8 T at room temperature, $\sim$3 times larger than the thin film value and $\sim$50 times larger than that of the gas phase condensed nanoparticles. The hysteresis curve is well explained by the Stoner-Wohlfarth model for non-interacting single-domain nanoparticles with the $H_{\rm c}$ distributed from 1 T to 5 T.

Extremal Myers-Perry black holes coupled to Born-Infeld electrodynamics in five dimensions

We construct a new class of perturbative extremal charged rotating black hole solutions in five dimensions in the Einstein--Born-Infeld theory. We start with an extremal five-dimensional Myers-Perry black hole seed in which the two possible angular momenta have equal magnitude, and add Born-Infeld electrical charge keeping the extremality condition as a constraint. The perturbative parameter is assumed to be the electric charge $q$ and the perturbations are performed up to 4th order. We also study some physical properties of these black holes. It is shown that the perturbative parameter $q$ and the Born-Infeld parameter $\beta$ modify the values of the physical quantities of the black holes. The solution suggests that the magnetic moment and gyromagnetic ratio of the black hole spacetime change sign when the Born-Infeld character of the solution starts to depart strongly from the Maxwell limit. We venture an interpretation for the effect.

Quantitative experimental determination of site-specific magnetic structures by transmitted electrons

Understanding the magnetic structure of materials on a nanometre scale provides fundamental information in the development of novel applications. Here we show a site-specific electron energy-loss magnetic chiral dichroism method, first experimentally demonstrating that the use of transmitted electrons allows us to quantitatively determine atomic site-specific magnetic structure information on a nanometre scale. From one NiFe(2)O(4) nanograin in composite films, we extract its atomic site-specific magnetic circular dichroism spectra and achieve the quantitative magnetic structure information, such as site-specific total magnetic moments and orbital to spin magnetic moment ratios, by constructively selecting the specific dynamical diffraction conditions in electron energy-loss magnetic chiral dichroism experiments. The site-specific electron energy-loss magnetic chiral dichroism method shows its unique ability for solving the site-specific magnetic structure at nanoscale resolution, compared with X-ray magnetic circular dichroism and neutron diffraction. This work opens a door to meet the challenge of exploring the magnetic structures of magnetic materials at the nanoscale using transmitted electrons.