Spontaneous Magnetic Moment Research Articles

Influence of Ru on the Magnetic Properties of Y<sub>2</sub>T<sub>17</sub> (T = Co, Fe)

Influence of Ru substitution on magnetic properties of Y2Fe17and Y2Co17(hexagonal structure of the Th2Ni17-type) has been studied on single-crystalline samples. Whereas in the Y2Fe17-xRuxsystem ferromagnetism is transformed rapidly into antiferromagnetism with a field-induced metamagnetic transition, in Y2Co17-xRuxonly a monotonous decrease of spontaneous magnetic moment, Curie temperature and first anisotropy constant is observed.

First principles molecular dynamics study of nitrogen vacancy complexes in boronitrene

We present the results of first principles molecular dynamics simulations of nitrogen vacancy complexes in monolayer hexagonal boron nitride. The threshold for local structure reconstruction is found to be sensitive to the presence of a substitutional carbon impurity. We show that activated nitrogen dynamics triggers the annihilation of defects in the layer through formation of Stone–Wales-type structures. The lowest energy state of nitrogen vacancy complexes is negatively charged and spin polarized. Using the divacancy complex, we show that their formation induces spontaneous magnetic moments, which is tunable by electron or hole injection. The Fermi level s-resonant defect state is identified as a unique signature of the ground state of the divacancy complex. Due to their ability to enhance structural cohesion, only the divacancy and the nitrogen vacancy carbon-antisite complexes are able to suppress the Fermi level resonant defect state to open a gap between the conduction and valence bands.

Electrical Control of Multiferroic Orderings in Mixed‐Phase BiFeO3 Films

XMCD-PEEM images showing spontaneous magnetic moments in mixed-phase stripes, which can be electrically controlled through changing environmental ferroelectric and ferroelastic boundary conditions. The inset shows the corresponding ferroelectric domain structures. The arrows indicate the in-plane polarization directions of the matrixes and the mixed-phase boundaries. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Magnetic measurements at pressures above 10 GPa in a miniature ceramic anvil cell for a superconducting quantum interference device magnetometer

A miniature ceramic anvil high pressure cell (mCAC) was earlier designed by us for magnetic measurements at pressures up to 7.6 GPa in a commercial superconducting quantum interference magnetometer [N. Tateiwa et al., Rev. Sci. Instrum. 82, 053906 (2011)]. Here, we describe methods to generate pressures above 10 GPa in the mCAC. The efficiency of the pressure generation is sharply improved when the Cu-Be gasket is sufficiently preindented. The maximum pressure for the 0.6 mm culet anvils is 12.6 GPa when the Cu-Be gasket is preindented from the initial thickness of 300-60 μm. The 0.5 mm culet anvils were also tested with a rhenium gasket. The maximum pressure attainable in the mCAC is about 13 GPa. The present cell was used to study YbCu(2)Si(2) which shows a pressure induced transition from the non-magnetic to magnetic phases at 8 GPa. We confirm a ferromagnetic transition from the dc magnetization measurement at high pressure. The mCAC can detect the ferromagnetic ordered state whose spontaneous magnetic moment is smaller than 1 μ(B) per unit cell. The high sensitivity for magnetic measurements in the mCAC may result from the simplicity of cell structure. The present study shows the availability of the mCAC for precise magnetic measurements at pressures above 10 GPa.

Room temperature spontaneous magnetization in calcined trioctylphosphine-ZnO nanoparticles

In this work, it is demonstrated that capping with trioctylphosphine oxide (TOPO) induces a ferromagnetic response in free-standing ZnO nanoparticles upon calcination without the necessity of metallic doping. Samples were synthesized by precipitation of zinc acetate solutions in a basic medium followed by capping with TOPO and heat treatment in static aerobic conditions. Nanoparticles show a wurtzite-type structure with an average size of 14 nm, and magnetization measurements evidence a spontaneous magnetic moment at room temperature for calcined nanoparticles, in contrast with the diamagnetic response observed in non-calcined TOPO-capped nanoparticles. Giving the absence of any magnetic impurity or metal dopant that could account for the total magnetization, it is proposed that the magnetism would be consistent with a charge transfer mechanism promoted by a phosphorous doping upon calcination of TOPO over the nanoparticles. This situation leads to a spontaneous magnetic moment by the local fulfillment of Stoner’s criterion for ferromagnetism at the nanoparticles surface.

Annealing temperature dependence of crystal structures and magnetic properties of Fe2CrAl and Fe2CrGa Heusler alloys

The crystal structures, spontaneous magnetic moment, Is, and the Curie temperature, TC, of Fe2CrAl and Fe2CrGa Heusler alloys were investigated. Single phases of A2, B2 and L21-type structures were obtainable in Fe2CrAl alloy by controlling the annealing temperature. The values of the Is and TC of the A2-type phase were 2.2μB/f.u. and 316K and those of the B2-type phase were 2.0μB/f.u. and 274K, larger than those of the L21-type phase of 1.6μB/f.u. and 210K, respectively. A single phase of the A2-type phase in Fe2CrGa alloy was obtained and the Is and TC were about 2.8μB/f.u. and 353K, respectively. The B2 or L21-type single phases of Fe2CrGa alloy could not be obtained because of the inevitable precipitants.

Magnetic properties of a DyFe 5Al 7 single crystal

A single crystal of DyFe 5Al 7 (tetragonal ThMn 12 structure) has been studied. DyFe 5Al 7 orders ferrimagnetically at T C = 231 K and has a compensation of the Dy and Fe sublattices at T comp = 93 K. Magnetization isotherms measured along the principal axes of the single crystal indicate that the magnetic moments lie in the basal plane of the tetragonal lattice. Strong magnetic anisotropy is observed not only between the basal plane and the [0 0 1] axis but also within the basal plane, with the [1 0 0] axis being the easy magnetization direction with the spontaneous magnetic moment 2.1 μ B. A very high coercivity with H c values up to 3 T was found at 2 K. In the temperature range 75–100 K, the compound exhibits a field-induced magnetic transition along the easy [1 0 0] direction. Temperature dependence of the critical field H cr of the transition is very strong, the value of H cr evidently exceeds 14 T below 75 K. A model for the magnetization process of a two-sublattice ferrimagnet with a weak intersublattice exchange interaction has been developed to explain the magnetic transition. The model reproduces the temperature behavior of H cr near the compensation point.

Magnetic properties of new compounds RuMn 2Sn and RuMn 2Si

New compounds RuMn 2Z (Z = Si, Sn) have been synthesized. X-ray diffraction measurements have confirmed that RuMn 2Z (Z = Si, Sn) crystallizes in a Heusler-like cubic structure. The lattice parameters of RuMn 2Si and RuMn 2Sn at room temperature are estimated to be 5.8260 Å and 6.2195 Å, respectively. Magnetization measurements have been carried out in fields up to 50 kOe for RuMn 2Z (Z = Si, Sn). Furthermore, the temperature dependence of initial permeability of RuMn 2Sn has been studied. RuMn 2Sn shows ferrimagnetic behavior. The spontaneous magnetic moment at 5 K and the Curie temperature of RuMn 2Sn are found to be of 1.68 μ B/f.u. and 272.1 K, respectively. RuMn 2Si exhibits spin-glass-like behavior with a freezing temperature estimated to be about 50 K.

Magnetoelastic effects in SrTi1−xMxO3(M = Fe, Co, or Cr) epitaxial thin films

SrTi${}_{1\ensuremath{-}x}$M${}_{x}$O${}_{3}$ films in which M = Fe, Co, or Cr and $x=0.04$--0.5 have been grown epitaxially on CeO${}_{2}$-buffered Si, SrTiO${}_{3}$, and LaAlO${}_{3}$ substrates. Films grown in vacuum containing Fe or Co typically showed a strong uniaxial magnetic anisotropy in the out-of-plane direction, a saturation moment on the order of 0.5\ensuremath{\mu}${}_{\mathrm{B}}$/Fe or Co, and a magnetization that persists to temperatures of order 1000 K. In contrast, films containing Cr showed no evidence of a spontaneous magnetic moment. The films are typically in a high in-plane compressive strain state due to epitaxial growth. The results are discussed in terms of the magnetoelastic effects from specific ionic valence states, and the magnetization versus temperature curves are fitted to a model for magnetoelastic spin ordering.

Intrinsic magnetic moments of gold nanoparticles

In this study the intrinsic magnetic moments developed in 4 nm bare fcc Au nanoparticles were investigated. The magnetization curves reveal a Langevin magnetic field profile, reflecting the existence of spontaneous magnetic moments. Neutron diffraction measurements detect a ferromagnetic moment. The magnetic diffraction patterns are consistent with a moment of $\ensuremath{\langle}{\ensuremath{\mu}}_{Z}\ensuremath{\rangle}=0.14$ \ensuremath{\mu}${}_{B}$ points in the crystallographic [111] direction at 5 K. Magnetostatic interparticle interactions weaken the localized magnetic moments but enhance the conduction electron density. These behaviors can be understood by considering the merging of the 5$d$ and 6$s$ electron bands triggered by finite-size effects and the lifting of band mixture by interparticle interactions.

Superparamagnetic-like behavior and spin–orbit coupling in (Co,Zn)RE 4W 3O 16 tungstates (RE=Nd, Sm, Eu, Gd, Dy and Ho)

Magnetic susceptibility measurements carried out on (Co,Zn)RE 4W 3O 16 compounds revealed a disordered state of magnetic moments above 4.2 K for all compounds under study, and a weak response to magnetic field and temperature for ZnSm 4W 3O 16 and ZnEu 4W 3O 16 samples. The temperature independent component of magnetic susceptibility has a negative value for ZnGd 4W 3O 16 and a positive one for the rest of the tungstates, indicating a domination of van Vleck contribution. The magnetization isotherms of majority of the tungstates under study revealed both spontaneous magnetic moments and hysteresis characteristic for the superparamagnetic-like behavior with blocking temperature T B ∼30 K, except for ZnEu 4W 3O 16. Fitting procedure of the Landé factor revealed that the stronger the orbital contribution, the weaker the superparamagnetic effect, namely for ZnRE 4W 3O 16. In case of CoRE 4W 3O 16 a significant participation of the Co 2+ moment in the spontaneous magnetization was observed.

Phase transformations and magnetotransport properties of the Pr0.5Sr0.5Co1 − x Mn x O3 system

The structural, magnetic, and magnetotransport properties of Pr0.5Sr0.5Co1 − x Mn x O3 (x 0.5, it is described by orthorhombic space group Imma. When the temperature decreases, a structural transformation without changing the symmetry takes place in all compounds. This transformation is caused by an active role of the inner shells of the praseodymium ion in chemical bond formation. The substitution of manganese for cobalt breaks a long-range ferromagnetic order near x ≈ 0.25, and a metal-dielectric transition occurs at x ≈ 0.15. The negative magnetoresistance is found to be maximal near a critical manganese concentration, where a long-range magnetic order is broken; it reaches 95% in a field of 14 T at T = 10 K for x = 0.2. An unusual dielectric magnetic state with a small spontaneous magnetic moment and a sharp transition into a paramagnetic state at T > 200 K is revealed in the concentration range 0.30 ≤ x ≤ 0.65 in spite of the absence of coherent magnetic neutron scattering. A model is proposed to explain the behavior of the magnetic properties in this phase.

Magnetism induced by capping of non-magnetic ZnO nanoparticles

Magnetism of 10 nm size capped nanoparticles, NPs, of non-magnetic ZnO is analysed in terms of the surface band since, as magnetic dichroism analysis has pointed out, impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. Due to the nanometric scale of the particles the kinetic energy spectrum of the surface states can be considered as discrete. Therefore, the magnetic polarisation cannot be easily induced by pumping electrons to energy levels above the Fermi energy. It is in the Fermi level itself, generally unfilled, that develops a spontaneous magnetic moment similarly to that induced by Hund rules in unfilled atomic orbitals. It is shown, however, that the total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 102 or 103 Bohr magnetons.

High-field magnetization of a Dy 2Fe 14Si 3 single crystal

The magnetization of a Dy 2Fe 14Si 3 single crystal was measured at 4.2 K in pulsed fields up to 51 T along the principal axes. The compound orders ferrimagnetically at 500 K, has a spontaneous magnetic moment of 8 μ B/f.u. (at 4.2 K) and exhibits a very large magnetic anisotropy, 〈1 0 0〉 being the easy axis. In fields applied along the 〈1 0 0〉 and 〈1 2 0〉 axes, field-induced phase transitions are observed at 33 T and at 39 T, respectively. The c-axis magnetization curve crosses the easy-axis curve at 19 T. At higher fields, for all directions, the magnetization continues to increase due to further bending of the sublattice moments. Temperature evolution of magnetic anisotropy and magnetic hysteresis are discussed as well.

Non-magnetic to Magnetic Transition under High Pressure in Narrow-Gap Semiconductor β-US2

We have measured the magnetization of an uranium chalcogenide compound β-US 2 under high pressure by piston cylinder and indenter type cells up to 2.42 GPa in a commercial SQUID magnetometer. The compound is a narrow-gap semiconductor that does not order magnetically down to 0.3 K at 1 bar. The appearance of a pressure-induced phase above 2 GPa was suggested by a previous study with the electrical resistivity measurement under high pressure. In this study, it was found that a ferromagnetic state is induced above 1 GPa. The pressure phase diagram were obtained. The values of the spontaneous magnetic moment at 0 K are less than 0.1 µ B /U, suggesting that the pressure-induced phase is a very weak ferromagnetic state. Considering the CEF singlet ground state in β-US 2 , it is suggest that the ferromagnetic state is an “induced-magnetic phase” often observed in some praseodymium compounds such as Pr 3 Tl. The experimental results are discussed in terms of the mean field theory.

Transition from Itinerant Electron Magnetism to Localized Spin Magnetism in Ni<sub>3</sub>Al<sub>1-Y</sub>Mn<sub>y</sub> Alloys

Magnetic properties of Ni3Al1-yMny alloys at y≤0.6 were investigated at T≤400 K in magnetic fields H≤4 MA/m. The concentration y dependencies of the spontaneous magnetic moment s, the effective magnetic moment eff, the Curie temperature ТС, the Weiss constant , and the temperature independent part of the magnetic susceptibility 0 were determined. The behavior of the Rhodes-Wohlfarth parameter р(y) in the transition region from the itinerant electron magnetism to the spin localized one is related to the increase in the spontaneous magnetic moment of Ni atoms inversely proportional to the average distance between Mn atoms with the highly localized magnetic moments.

MAGNETIC PROPERTIES Cu DOPED ZnO:Fe SEMICONDUCTORS

Magnetization measurements were performed on a series of Zn 0.9-x Fe 0.1 Cu x O samples (0 ≤ x ≤ 0.10). Small hysteresis losses are seen at low temperatures. The ferromagnetic exchange interaction has been evaluated from the inverse DC magnetic susceptibility versus T and the molecular field theory. We found that Cu -doping greatly enhances the FM exchange interaction, increases the saturation magnetization, hysteresis losses and the magnetic susceptibility. Arrott-Kouvel plot has been used to study the spontaneous magnetic moment at low temperatures. We show that hysteresis losses cannot be taken as the only evidence for the appearance of the ferromagnetic order in these semiconducting semi-magnetic materials.

First-Order Magnetic Phase Transitions in Anisotropic Itinerant Electron Ferromagnets

A spin fluctuation model is proposed for itinerant electron weak ferromagnets with Ising-like magnetic anisotropy. According to our theory of itinerant electron magnets, the temperature dependence of the magnetic susceptility and the spontaneous magnetic moment is studied. In contrast to those in isotropic cases, magnetic transitions in the model become of first order because of the oversuppression of thermal spin fluctuation amplitude around the critical point that hinders the spontaneous moment to diminish continuously.

The interrelation of magnetic and dielectric properties ofCoxMn1 − xS solid solutions

Magnetization of the cation-substitutedCoxMn1 − xS sulfides upon cooling in zero and 100 Oe magnetic fields at the temperatures4–300 K has been measured. Permittivity of these materials at frequencies from 1to 100 kHz in magnetic and dc electric fields in the 100–300 K temperaturerange has been determined. Change in the dielectric permittivity under anexternal magnetic field is found to have a maximum in the temperature ranges ofT1 ∼ (110–120 K) andT2 ∼ (230–250 K). Formation of spontaneous magnetic moment and the rise ofmagnetic susceptibility are revealed at the same temperatures in theCoxMn1 − xS solid solutions. Features of the magnetoelectric properties of the sulfides have beenexplained by orbital ordering.

Interrelation of the magnetic structure and the band insulating state in doped manganites

The interrelation between the magnetic structure and the band insulating state in doped La1 − xCaxMnO3 manganites has been discussed. An analysis of various zigzag chains has revealed that, in the one-dimensional spectrum of eg electrons of these compounds, there always appear a number of band gaps, which at certain electron concentrations x support the formation of an insulating state in the corresponding three-dimensional antiferromagnetic structures. Apart from the well-known spectra of chains of the type (1 × 1) (magnetic E-structure) and (2 × 2) (magnetic CE-structure), we have obtained for the first time the spectrum of a (3 × 3) zigzag chain, whose three-dimensional unit cell contains 24 manganese atoms and provides a qualitatively correct fit to the magnetic structure of the La1/3Ca2/3MnO3 manganite. As follows from our analysis, the formation of a magnetic structure in this manganite should also be accompanied by the generation of a spontaneous magnetic moment.