Configuration Of Magnetic Moments Research Articles

Double stranded antiferromagnetic helix as an efficient spin filter

We report a large degree of spin filtration in a double stranded (ds) antiferromagnetic helix (AFH) system. Generally spin channel separation is not possible when a magnetic system possesses a vanishing net magnetization. But we show that a highly polarized spin current can be obtained through the ds AFH when it is subjected to a transverse electric field. Describing the physical system within a tight-binding framework, spin-dependent transport phenomena are studied using the well known Green’s function formalism. The effects of chirality (left-handed and right-handed), electric field, electronic hopping (short-range and long-range) in each strand, system temperature, and size of the helix on spin filtration are critically investigated. Two different configurations of magnetic moments in the helix are taken into account, for a more general description. Suitably adjusting the physical parameters, almost cent percent spin polarization can be substantiated and that feature persists even for a broad parameter range. Our analysis may open up a new direction for achieving spin-selective electron transmission and designing of controlled spintronic devices using similar kinds of fascinating helical magnetic systems.

Reversible Thermal Hysteresis in Heating‐Cooling Cycles of Magnetic Susceptibility: A Fine Particle Effect of Magnetite

AbstractThermomagnetic curves of magnetic susceptibility (κ) are key to characterizing magnetic properties. We report hump‐shaped κ‐T curves of magnetite‐bearing basalt during heating‐cooling cycles to ∼340°C, with a large thermal hysteresis and similar starting and ending values, even in multiple repeated cycles, ruling out changes in magnetic mineralogy. Based on FORC diagrams and published results of engineered materials, we propose that thermal hysteresis arises from configurations of magnetic moments in clusters of single‐domain particles due to dipolar coupling, with different collective behavior during heating and cooling. This effect modifies the hump‐shaped thermal relaxation behavior of the individual nanoparticles. FORC and κ‐T results indicate an increase in effective particle sizes after 700°C‐heating. Our results are a warning against premature interpretation of a decreasing trend in κ‐T curves by maghemite inversion. Instead, fine particle behavior should be considered when a hump‐shaped κ‐T behavior is detected.

Observation of spin-glass-like characteristics in ferrimagnetic TbCo through energy-level-selective approach

Rare earth (RE)–transition metal (TM) ferrimagnetic alloys are gaining increasing attention because of their potential use in the field of antiferromagnetic spintronics. The moment from RE sub-lattice primarily originates from the 4f-electrons located far below the Fermi level (EF), and the moment from TM sub-lattice arises from the 3d-electrons across the EF. Therefore, the individual magnetic moment configurations at different energy levels must be explored to clarify the microscopic mechanism of antiferromagnetic spin dynamics. Considering these issues, here we investigate the energy-level-selective magnetic moment configuration in ferrimagnetic TbCo alloy. We reveal that magnetic moments at deeper energy levels are more easily altered by the external magnetic field than those near the EF. More importantly, we find that the magnetic moments at deeper energy levels exhibit a spin-glass-like characteristics such as slow dynamics and magnetic moment freezing whereas those at EF do not. These unique energy-level-dependent characteristics of RE-TM ferrimagnet may provide a better understanding of ferrimagnet, which could be useful in spintronic applications as well as in spin-glass studies.

Transition from antiferromagnetic to quadrupole order in a modified square artificial spin ice

The results of a numerical study of an ordered substitution of a double-segment into the unit cell of square artificial spin ice are presented. Each pattern vertex has three magnetic moment configurations that compete to form a magnetic ground state in zero applied magnetic field, including nearest-neighbor and next-nearest-neighbor interaction contributions to the total magnetostatic energy. The ground state depends on the number of lattice sites considered and the spacing between the two film segments that comprise the double segment. Monte Carlo simulations reveal that the double-segment sublattice undergoes long-range antiferromagnetic order that can be supplanted by magnetic quadrupole order by applying an in-plane magnetic field perpendicular to the double-segment easy axis. The quadrupole-ordered state consists of a sublattice of weakly correlated chains of double-segments with antiparallel polarizations, which admits many different ground states that reflect a very high degree of frustration.

Highly Tunable Magnetic Phases in Transition-Metal Dichalcogenide Fe1/3+δNbS2

A change in magnetic moment configurations as a function of iron ratio in Fe${}_{1/3+\ensuremath{\delta}}$NbS${}_{2}$ underlies its current-induced resistance switching, a key insight for using this and similar materials in future spintronic devices.

Electric-field tunable rotation of optical mode ferromagnetic resonance in FeCoB/Ru/FeCoB/PMN-PT multilayers

FeCoB/Ru/FeCoB trilayers with a uniaxial magnetic anisotropy were deposited on (011)-cut lead magnesium niobate-lead titanate (PMN-PT) single crystal ferroelectric substrates using a compositional gradient sputtering (CGS) method. Ultrahigh optical mode resonance frequencies from 11.76 to 18.96 GHz at zero magnetic field were achieved due to the strong interlayer exchange coupling between FeCoB films through Ru spacer. In this study, two orthogonal magnetic anisotropic fields (one is CGS induced anisotropy field HKCGS and the other is the piezoelectric stress-induced anisotropy field HKME) were set to realize electric-field (E-field) controlled switch of magnetic moment configuration through their competition. As a result, the optical mode resonance intensity can make reversible 90° rotation under applied E-field, while the advantages of ultrahigh frequency optical mode resonance in trilayers are still maintained because the interlayer exchange coupling is not destroyed by magnetoelectric coupling. The ultrahigh resonance frequency and E-field tunable and reversible FMR rotation in these trilayers provide a potential route to guide microwave flow in multifunctional microwave and spintronic devices.

Local Spin Ice Order Induced Planar Hall Effect in Nd–Sn Artificial Honeycomb Lattice

AbstractGeometrically frustrated materials, such as spin ice or kagome lattice, are known to exhibit exotic Hall effect phenomena due to spin chirality. For the first time, Hall effect mechanism is explored in an artificial honeycomb spin ice of Nd–Sn element using Hall probe and polarized neutron reflectivity measurements. In an interesting observation, a strong enhancement in Hall signal at relatively higher temperature of T ∼ 20 K is detected. The effect is attributed to the planar Hall effect due to magnetic moment configuration in spin ice state in low field application. In the antiferromagnetic state of neodymium at low temperature, applied field induced coupling between atomic Nd moments and conduction electrons in underlying lattice causes distinct increment in Hall resistivity at very modest field of H ∼ 0.015 T. The experimental findings suggest the development of a new research vista to study the planar and the field induced Hall effects in artificial spin ice.

Magnetic moment configuration: One of decisive factors to enhance the optical mode resonance in interlayer exchange coupled trilayers

The optical mode (OM) ferromagnetic resonance (FMR) pushes the frequency of soft magnetic films from 10 to 20 GHz, showing a great engineering application prospect in monolithic microwave integrated circuits. However, the determinants of OM frequency and intensity remain unclear. In this study, three magnetic moment configurations (MMCs) with uniaxial anisotropy, quasi-isotropy, and isotropy were established respectively to explore the effect of MMCs on the OM FMR performances in FeCoB/Ru/FeCoB trilayers with the same average compositions and geometry. No detectable FMR signal was observed in the isotropic sample, while an ultrahigh OM frequency frO of 15.91 GHz with parentheses-shaped angle distribution of FMR intensity was present in the uniaxial anisotropic sample. In contrast, a high frO of 13.29 GHz also exists in the quasi-isotropic sample, but its angle distribution of FMR intensity likes a circle, indicating an omnidirectional frO distribution. This sample is very beneficial for the OM engineering application due to its omnidirectional frO distribution, which breaks through the limitation of magnetic anisotropy to the shape design of magnetic microwave components. It can be concluded that, although three trilayers have the same compositions and geometry, completely different OM resonance performances result from the difference of MMCs, i.e. the MMC is a decisive factor for OM resonance. This study provides the design basis and optimization method for magnetic material fabrication and their device design.

Transition from Antiferromagnetic to Quadrupole Order in a Modified Square Artificial Spin Ice

The results of a numerical study of an ordered substitution of a double-segment into the unit cell of square artificial spin ice are presented. Each pattern vertex has three magnetic moment configurations that compete to form a magnetic ground state in zero applied magnetic field, including nearest-neighbor and next-nearest-neighbor interaction contributions to the total magnetostatic energy. The ground state depends on the number of lattice sites considered and the spacing between the two film segments that comprise the double segment. Monte Carlo simulations reveal that the doub le-segment sublattice adopts long-range antiferromagnetic order that can be supplanted by magnetic quadrupole order by applying an in-plane magnetic field perpendicular to the double-segment easy axis. The quadrupole-ordered state consists of a sublattice of weakly correlated chains of double-segments with antiparallel polarizations, which admits many different ground states that reflect a very high degree of frustration.

Influence of Pr substitution on the physical properties of the Ce1−xPrxCoGe3 system: Combined experimental and first-principles study

We present the results of our investigations of physical properties for the novel Ce$_{1-x}$Pr$_x$CoGe$_3$ system performed with a number of experimental methods: magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance, and thermoelectric power. Moreover, the electronic structure was studied by means of photoelectron spectroscopy measurements and first-principles calculations. All investigated compositions of the Ce$_{1-x}$Pr$_x$CoGe$_3$ series crystallize in the tetragonal BaNiSn$_3$-type structure. The lattice parameters and unit cell volumes decrease with increasing Pr concentration. On the basis of the measurements taken, a preliminary magnetic phase diagram was created. A continuous suppression of the long-range magnetic ordering was observed with increase of Pr concentration. The critical Pr concentration for magnetic moment ordering was determined from linear extrapolation of the ordering temperature $versus$ $x$ to the lowest temperatures ($T = 0$ K) and is equal to about 0.66. Based on the first-principles calculations we show how the substitution of Pr for Ce affects the electronic structure and magnetic properties of the considered alloys. Within a single model we take into account the magnetic ordering, fully-relativistic effects, and Hubbard U repulsion on Ce and Pr. The impact of Hubbard U on the results of calculations is also discussed. We present the valence-band analysis, Mulliken electronic population analysis, and calculated electronic specific heat coefficients. For CeCoGe$_3$ it is found that the $++--$ configuration of magnetic moments on Ce is slightly more stable than the $+-+-$ one, and also that the calculated value of total magnetic moment on Ce (including spin and orbital parts) is in good agreement with the measurements.

Stable states of vortex-like magnetic formations in inhomogeneous magnetically uniaxial films and their behavior in a longitudinal magnetic field

This paper looks into the magnetization reversal processes of uniaxial ferromagnetic films with spatially modulated material parameters. It has been established that four types of vortex-like inhomogeneities can form on columnar defects of a certain type in such films, with these inhomogeneities having a nontrivial configuration of magnetic moments and differing in their topological parameters. It has been shown that in a magnetic field, their structure transforms into two or three stages, such transformation depending both on the topological charge and on the polarity of their core. A diagram of their stable states has been constructed, and a range of material parameters has been determined within which they can exist only in the presence of a magnetic field. The methods for producing such films have been considered.

Unraveling magneto-structural coupling of Ni2MnGa alloy under the application of stress and magnetic field using in situ polarized neutron diffraction

The magneto-structural evolution of a Ni2MnGa single crystal was investigated by in situ polarized neutron diffraction under both magnetic field and mechanical loading. The ability to separate the nuclear and magnetic scatterings by polarized neutrons enables simultaneous observations of the twin reorientation (through twin boundary motion) and magnetic moment configuration. It is found that under a 1.0 T saturating magnetic field, twin reorientation can be activated by compressive stress and is accompanied by a realignment of the magnetic moment, which follows the easy axis of the twin variant. On the other hand, compressive stress as small as 1.0 MPa can freeze the twin reorientation. The evolution of the magnetic scattering amplitudes suggests that the change in magnetization was mainly achieved through the magnetic domain wall motion, while the twin boundary motion was blocked.

From Atomic Level to Large-Scale Monte Carlo Magnetic Simulations.

This paper refers to Monte Carlo magnetic simulations for large-scale systems. We propose scaling rules to facilitate analysis of mesoscopic objects using a relatively small amount of system nodes. In our model, each node represents a volume defined by an enlargement factor. As a consequence of this approach, the parameters describing magnetic interactions on the atomic level should also be re-scaled, taking into account the detailed thermodynamic balance as well as energetic equivalence between the real and re-scaled systems. Accuracy and efficiency of the model have been depicted through analysis of the size effects of magnetic moment configuration for various characteristic objects. As shown, the proposed scaling rules, applied to the disorder-based cluster Monte Carlo algorithm, can be considered suitable tools for designing new magnetic materials and a way to include low-level or first principle calculations in finite element Monte Carlo magnetic simulations.

Triangular magnetic structure of the Mn3Sb compound

The Mn3Sb metastable compound is formed at high pressure and temperature and it decomposes upon heating above 420 K into Mn2Sb and Mn. It has a cubic crystalline structure describing the Pm-3m (№ 221) space group with a lattice parameter of a = 0.400 nm. In the present work, according to the results of neutron diffraction investigations and taking into account magnetometry data, it is shown that Mn3Sb is an antiferromagnet, and a model of the magnetic structure with a triangular configuration of equal magnetic moments in magnitude is proposed. The magnetic moments of manganese atoms, constituting the basis of a unit magnetic cell, lie in the (111) plane and form an equilateral triangle. According to neutron diffraction data, the magnetic moments of manganese atoms were determined at different temperatures.

Magnetic ground state in FeTe2,VS2 , and NiTe2 monolayers: Antiparallel magnetic moments at chalcogen atoms

Our analysis based on the results of hybrid and semilocal density-functional calculations with and without Hubbard $U$ correction for on-site Coulomb interactions reveals the true magnetic ground states of three transition-metal dichalcogenide monolayers, viz., ${\mathrm{FeTe}}_{2},{\mathrm{VS}}_{2}$, and ${\mathrm{NiTe}}_{2}$, which comprise inhomogeneous magnetic moment configurations. In contrast to earlier studies considering only the magnetic moments of transition-metal atoms, the chalcogen atoms by themselves have significant, antiparallel magnetic moments owing to the spin polarization through $p\text{\ensuremath{-}}d$ hybridization. The latter is found to be true for both $H$ and $T$ phases of ${\mathrm{FeTe}}_{2},{\mathrm{VS}}_{2}$, and ${\mathrm{NiTe}}_{2}$ monolayers. Our predictions show that the ${\mathrm{FeTe}}_{2}$ monolayer in its lowest-energy structure is a half metal, which prevails under both compressive and tensile strains. Half metallicity occurs also in the ${\mathrm{FeTe}}_{2}$ bilayer but disappears in thicker multilayers. The ${\mathrm{VS}}_{2}$ monolayer is a magnetic semiconductor; it has two different band gaps of different character and widths for different spin polarization. The ${\mathrm{NiTe}}_{2}$ monolayer, which used to be known as a nonmagnetic metal, is indeed a magnetic metal with a small magnetic moment. These monolayers with intriguing electronic and magnetic properties can attain new functionalities for spintronic applications.

Magnetic structure of the square cupola compound Ba(TiO) Cu4(PO4)4

The magnetic structure of the antiferromagnetic square cupola compound Ba(TiO)Cu$_4$(PO$_4$)$_4$ with the tetragonal structure is studied with 31P nuclear magnetic resonance techniques. The magnetic hyperfine shift K shows a clear splitting at the N\'eel temperature T$_N$ = 9.5 K, where the resonance splits into two lines when an external magnetic field is oriented along the c axis and into four lines when the field is along the a axis. In the paramagnetic region K(T) follows temperature dependence of the magnetic susceptibility $\chi(T)$. From K vs $\chi$ plot we determined nearly isotropic hyperfine field values Ha_hf = 765 mT/$\mu_B$ and Hc_hf = 740 mT/$\mu_B$ for the magnetic field oriented along a and c, respectively. From the rotation of the single crystal in the external magnetic field we determined eight different orientations of K-tensor in the paramagnetic region. In the antiferromagnetic state at T = 6 K we found that the local field at phosphorus is mainly due to dipolar field of coppers. Here the rotation of the single crystal shows eight different orientations of the local field Bint = 35.6 mT. The orientations correspond to the calculation of dipolar fields at phosphorus assuming magnetic quadrupolar configuration of magnetic moments $\varGamma_3(1)$ described previously [Nat. Commun. 7, 13039 (2016); Phys. Rev. B 96, 214436 (2017)].

Tunable induced magnetic moment and in-plane conductance of graphene in Ni/graphene/Ni nano-spin-valve-like structure: A first principles study

This study theoretically investigated the magnetic properties and electronic structure of a graphene-based nano-spin-valve-like structure. Magnetic nickel layers on both sides of the graphene were considered. A spin-polarized generalized-gradient approximation determined the electronic states. In an energetically stable stacking arrangement of graphene and two nickel layers, the anti-parallel spin configuration of the underlayer and overlayer magnetic moments had the lowest energy, which is in agreement with previous experimental studies. The spin density mapping and obtained band-structure results show that when the upper and lower Ni(111) slabs have an anti-parallel (parallel) magnetic-moment configuration, the carbon atoms of sublattices A and B will have an antiferromagnetic (ferromagnetic) spin configuration. A band gap at the Dirac cone was open when the alignment had an anti-parallel configuration and closed when the alignment had a parallel configuration. Therefore, the in-plane conductance of the graphene layer depends on the magnetic alignment of the two nickel slabs when the Fermi level is adjusted at the Dirac point. Both the magnetic properties and electronic structures of the Ni/graphene/Ni nanostructure cause the system to be a new prospective spintronic device showing controllable in-plane magnetoresistance.

Ferromagnetism induced by Cr, V single and double impurities doped BN from Ab-initio and Monte Carlo study

Using the Ab initio calculations and Monte Carlo (MC) simulations, we investigate the electronic and magnetic properties of cubic BN compound doped and co-doped with Chromium (Cr) and Vanadium (V) atoms. The calculated electronic band structure and density of states (DOS) of doped BN with single and double impurities can induce localized edge states around Fermi level, leading from semiconductor to half-metal transition. Thereafter, the stability of ferromagnetic (FM) ordering and disordered local magnetic moment (DLM) configurations has been explored. The interesting Curie temperature (Tc), magnetization and susceptibility results for the various concentrations of Chromium (Cr) and Vanadium (V) co-doped (doped) BN suggest a vast exploitation attention in spintronic applications.

First-principles Theory of Magnetic Multipoles in Condensed Matter Systems

The multipole concept, which characterizes the spacial distribution of scalar and vector objects by their angular dependence, has already become widely used in various areas of physics. In recent years it has become employed to systematically classify the anisotropic distribution of electrons and magnetization around atoms in solid state materials. This has been fuelled by the discovery of several physical phenomena that exhibit unusual higher rank multipole moments, beyond that of the conventional degrees of freedom as charge and magnetic dipole moment. Moreover, the higher rank electric/magnetic multipole moments have been suggested as promising order parameters in exotic hidden order phases. While the experimental investigations of such anomalous phases have provided encouraging observations of multipolar order, theoretical approaches have developed at a slower pace. In particular, a materials' specific theory has been missing. The multipole concept has furthermore been recognized as the key quantity which characterizes the resultant configuration of magnetic moments in a cluster of atomic moments. This cluster multipole moment has then been introduced as macroscopic order parameter for a noncollinear antiferromagnetic structure in crystals that can explain unusual physical phenomena whose appearance is determined by the magnetic point group symmetry. It is the purpose of this review to discuss the recent developments in the first-principles theory investigating multipolar degrees of freedom in condensed matter systems. These recent developments exemplify that ab initio electronic structure calculations can unveil detailed insight in the mechanism of physical phenomena caused by the unconventional, multipole degree of freedom.

Dynamics of a lattice of magnetic nanoparticles under action of a pulse of a magnetic field

Processes of quasistatic and dynamic magnetization reversal have been studied for the case of planar 6 × 6 lattices of magnetic nanodipoles that possess a cubic crystallographic anisotropy. The response of the total magnetic moment to a magnetic-field pulse of various duration and polarization have been determined for different equilibrium configurations of the lattices. Along with the in-plane configurations of magnetic moments, configurations with one and two dipoles oriented perpendicular to the plane of the lattices have been considered.