Magnetic Moment Distribution Research Articles

Impact of the magnetic proximity effect in Pt on the total magnetic moment of Pt/Co/Ta trilayers studied by x-ray resonant magnetic reflectivity

In this work, we study the influence of the magnetic proximity effect (MPE) in Pt on the total magnetic moment of thin film trilayer systems consisting of the ferromagnet (FM) Co adjacent to the heavy metals (HMs) Pt and Ta. We investigate the trilayer systems HM1/FM/HM2 with different stacking order as well as a reference bilayer without any MPE. X-ray resonant magnetic reflectivity (XRMR) is a powerful tool to probe induced magnetism, especially when buried at interfaces in a multilayer. By using XRMR, we are able to obtain magnetic depth profiles of the structural, optical and magnetic parameters. By fitting the experimental data with a Gaussian-like magnetooptic profile taking the structural roughness at the interface into account, we can extract the magnetic moment of the spin-polarized layer. Comparing the obtained moments to the measured total moment of the sample, we can determine the impact of the MPE on the total magnetic moment of the system. Such information can be critical for analyzing spin transport experiments, including spin-orbit torque and spin Hall angle measurements, where the saturation magnetization Ms has to be taken into account. Therefore, by combining magnetization measurements and XRMR methods we were able to get a complete picture of the magnetic moment distribution in these trilayer systems containing spin-polarized Pt.

Bismuth iron garnet: Ab initio study of electronic properties

Bismuth iron garnet (BIG), i.e. Bi3Fe5O12, is a strong ferrimagnet that also possess outstanding magneto-optical properties such as the largest known Faraday rotation. These properties are related with the distribution of magnetic moments on octahedral and tetrahedral sites, the presence of spin gaps in the density of state and a strong spin-orbit coupling. In this work, first-principles ab initio calculations are performed to study the structural, electronic and magnetic properties of BIG using Density Functional Theory with Hubbard+U (DFT+U) correction including spin-orbit coupling and HSE06 hybrid functional. We found that the presence of spin gaps in the electronic structure results from the interplay between exchange and correlation effects and the crystal field strengths for tetrahedral and octahedral iron sublattices. The DFT+U treatment tends to close the spin-gaps for larger U due to over-localization effects, notably in the octahedral site. On the other hand, the hybrid functional confirms the occurrences of three spin gaps in the iron states of the conduction band as expected from optical measurements. A strong exchange splitting at the top of the valence bands associated with a lone-pair type mixture of O p and Bi s,p states is also obtained. Similar exchange splitting was not previously observed for other iron based garnets, such as for yttrium iron garnet. It follows that hole doping, as obtained by Ca substitution at Bi sites, results in a full spin polarized density at the Fermi energy. This work helps to shed more light on the theoretical comprehension of the properties of BIG and opens the route towards the use of advanced Many Body calculations to predict the magneto-optical coupling effects in BIG in a direct comparison with the experimental measurements.

Scanning Magnetic Microscope Using a Gradiometric Configuration for Characterization of Rock Samples.

Scanning magnetic microscopy is a tool that has been used to map magnetic fields with good spatial resolution and field sensitivity. This technology has great advantages over other instruments; for example, its operation does not require cryogenic technology, which reduces its operational cost and complexity. Here, we presented a spatial domain technique based on an equivalent layer approach for processing the data set produced by magnetic microscopy. This approach estimated a magnetic moment distribution over a fictitious layer composed by a set of dipoles located below the observation plane. For this purpose, we formulated a linear inverse problem for calculating the magnetic vector and its amplitude. Vector field maps are valuable tools for the magnetic interpretation of samples with a high spatial variability of magnetization. These maps could provide comprehensive information regarding the spatial distribution of magnetic carriers. In addition, this approach might be useful for characterizing isolated areas over samples or investigating the spatial magnetization distribution of bulk samples at the micro and millimeter scales. This technique could be useful for many applications that require samples that need to be mapped without a magnetic field at room temperature, including rock magnetism.

Diode effect in the lateral spin valve

We propose a possible experimental setup for nonreciprocal electron transport in a lateral spin valve due to noncoplanar distribution of magnetic moment (and field) in the system. Some metals (Al, Cu) and semiconductors (GaAs, InSb etc) demonstrate spin accumulation even at room temperatures due to large spin flip lengths. The Hanle precession was observed in lateral spin valves based on such materials and two parallel magnetic electrodes. We provide theoretical estimations which show that the nonreciprocal effect in a configuration with non-parallel magnetic electrodes is of the same order of value as the effect that arise due to Hanle precession. This makes it possible to observe the nonreciprocal electron transport as a manifestation of the noncommutativity of spin-1/2 algebra for them in the proposed system. Such property of noncoplanar magnetic system has a potential of application in a noncoplanar type of spintronic devices.

Spatially separated spin carriers in three-ports graphene nanoribbons

Exporting the different spin signals to different ports is of practical importance to graphene-based spintronic devices. In this work, we have designed a three-ports graphene nanoribbon (GNR) device by inserting square-shaped carbon tetragon (CT) into GNR symmetrically, and calculated the magnetic moment distribution and transmission spectrum by using first-principles calculation and quantum transport simulation. Our results show that CT can bring non-equivalent path for two spin transport channels resulting in one spin is easier to transport than the other in each output port. Overall whole model, the spin states would be separated in real space but degenerated in energy. After correcting the device with asymmetric edge hydrogenation, we can achieve spatially separated spin carriers in real space and stable spin transporting. Our results suggest this model can serve as the most basic logic device for applying in future spintronics.

A micro-statistical constructive model for magnetization and magnetostriction under applied stress and magnetic fields

Magnetization and magnetostriction are of critical importance to understand the magnetic behavior of ferromagnetic materials under stress and magnetic fields. The micromechanism of magnetization (or magnetostriction) is determined by the probability of angular distribution of magnetic moments and saturation magnetization (or saturation deformation). Thus, the probability of angular distribution of magnetic moments is important to construct the relationship between the magnetization (or magnetostriction) and magnetic moments. In this letter, a new microstatistical model is developed to explain the magnetization and magnetostriction mechanisms for isotropic materials. The probability of angular distribution between magnetic moment and magnetic field is expressed by a modified Boltzmann distribution. The results calculated by the present model are compared with the experimental results. The values of the determination coefficient R2 indicate that the present model can accurately describe the relationship between magnetization and magnetostriction under both stress and magnetic fields.

Structural and Magnetic Properties of Six-Line Ferrihydrite Nanoparticles

Magnetic properties of antiferromagnetic nanoparticles are not as straight forward as for ferromagnetic and ferrimagnetic nanoparticles. We analyzed the data of antiferromagnetic six-line ferrihydrite nanoparticles by considering distribution in particle magnetic moment. The fit of magnetization data, using non-linear least square fit procedure, considering Langevin function with and without distribution in particle magnetic moment, is presented. Magnetization of the system is measured as function of temperature and applied magnetic field.

Multilayered and alloyed Fe-Co and Fe-Ni nanowires physicochemical studies

Anomalous deposition of multi-element nanowires continuously interests scientists to study such a system. In this paper, two types of magnetic nanowires were electrodeposited: multilayered and alloy-like. Fe-Co and Fe-Ni nanowires with various relative molar ratio were prepared by DC electrodeposition in aluminum oxide matrix, with a mean pore diameter of 140 ± 20 nm. The nanostructures were investigated in two states: released and within the matrix, using the following techniques: Scanning Electron Microscopy, Energy Dispersive X-ray spectroscopy, X-ray diffraction, Infrared, and Mössbauer spectroscopy. The Scanning Electron Microscopy showed that the length of Fe-(Co, Ni) nanowires is of the order of 3 µm and the diameter determined by the pores of the anodic aluminum oxide templates. The X-ray diffraction and Mössbauer spectroscopy also showed that the fabrication method allows for the obtainment of both multilayered as well as alloyed nanowires with tunable magnetic properties which depend on both the elements’ relative ratio and its ordering. The magnetic texture observed by Mössbauer measurements demonstrated the almost random distribution of magnetic moments of iron in the studied samples which are rather unusual in layered systems.

The Electronic and Magnetic Properties of Multi-Atom Doped Black Phosphorene.

Recently, substitutional doping is proved to be an effective route to induce magnetism to black phosphorene for its application in spintronics. Herein, we investigate the thermodynamic stability, electronic and magnetic properties of doped black phosphorene with multi Al or Cl atoms using first-principles calculations. We find these doped phosphorenes are thermodynamically stable at 0 K and the stability first improves and then deteriorates with the number of dopant atom increasing. Corresponding to the variety of stability, the amount of electrons transferred between impurity and neighboring phosphorus atoms also first increase and then reduce. However, the band gap of Al-doped phosphorene reduces monotonically from 0.44 eV to 0.13 eV while that of Cl-doped phosphorene first decreases from 0.10 eV to 0 and then becomes flat, which is a result of the impurity levels emerging and splitting. Besides, in doped phosphorenes with an even number of impurity atoms, the antiferromagnetic order is favored by energy. Through computing the magnetic moment and spin distribution, we further confirm the antiferromagnetic order existing only in the doped phosphorenes with two and four Cl atoms. These results may provide some help for future applications of black phosphorene in spintronics.

Effect of Thermal Annealing on the Stoichiometry and Magnetism of Mn–Ga Thin Films

MnxGa thin films (1.64 ≤ x ≤ 2) were grown at room temperature by molecular beam epitaxy on the native SiO2 layer of Si(100) commercial wafers. After growth, MnxGa films were thermally annealed at different temperatures (200, 300, and 400 °C). The X-ray diffraction results reveal D022-Mn2Ga as the main phase and an improvement of the crystalline quality as a function of the annealing temperature. The samples were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy, and vibrating sample magnetometry techniques. The magnetization curves suggest that the magnetic behavior is strongly dependent on the annealing time and temperature and that the saturation magnetization decreases with an increase in the Mn concentration in the alloy. These magnetic properties are related to the morphology and crystallinity of the samples. The magnetic moment distributions of the films were calculated using density functional theory, bringing a better understanding of the origin of the observed mag...

Magnetism in Cu2Si zigzag nanoribbon

The surface states of three dimensional topological nodal line semimetal (TNLSM) form a flat band within the projection of the closed nodal line onto the surface. Such a flat band implies a singular surface density of states which, if close to the Fermi energy, is apt to induce a magnetic phase transition. Similar physics is expected in a two-dimensional (2D) TNLSM. In the framework of density functional theory, we study the edge states of Cu2Si monolayer which is currently an experimentally feasible sample of 2D TNLSM. We find that the flat bands attached to two kinds of zigzag edges of Cu2Si are very close to the Fermi energy. Moreover, we explore the possible magnetism of Cu2Si nanoribbons terminated by these zigzag edges. We find that a narrow ribbon has ferromagnetic ground states with sizable magnetic moments, owing to the interaction between the edge states localized at the opposite edges. In addition, carrier doping in a nanoribbon can induce the transition between the ferromagnetic and nonmagnetic states. More interestingly, the magnetic moment distribution in real space from one to another edges can be readily modulated by the carrier doping. Our study indicates that Cu2Si nanoribbons with controllable magnetism provide a new platform to realize the device functions of spintronics.

Symmetry, spin-texture, and tunable quantum geometry in a WTe2 monolayer

The spin orientation of electronic wavefunctions in crystals is an internal degree of freedom, typically insensitive to electrical knobs. We argue from a general symmetry analysis and a $\vec k \cdot \vec p$ perspective, that monolayer 1T'-WTe$_2$ possesses a gate-activated canted spin texture that produces an electrically tunable bulk band quantum geometry. In particular, we find that due to its out-of-plane asymmetry, an applied out-of-plane electric field breaks inversion symmetry to induce both in-plane and out-of-plane electric dipoles. These in-turn generate spin-orbit coupling to lift the spin degeneracy and enable a bulk band Berry curvature and magnetic moment distribution to develop. Further, due to its low symmetry, Berry curvature and magnetic moment in 1T'-WTe$_2$ possess a dipolar distribution in momentum space, and can lead to unconventional effects such as a current induced magnetization and quantum non-linear anomalous Hall effect. These render 1T'-WTe$_2$ a rich two-dimensional platform for all-electrical control over quantum geometric effects.

Innovative released-active drug for the treatment of neurological diseases: Results of preclinical studies

A numerical inversion method known from the analysis of light scattering by colloidal dispersions is now applied to magnetization curves of ferrofluids. The distribution of magnetic particle sizes or dipole moments is determined without assuming that the distribution is unimodal or of a particular shape. The inversion method enforces positive number densities via a non-negative least squares procedure. It is tested successfully on experimental and simulated data for ferrofluid samples with known multimodal size distributions. The created computer program MINORIM is made available on the web.

Uncovering the magnetic properties of the AgxNiy (x+y=55) nanoalloys in the whole composition range

Nickel and silver are metals with interesting properties of technological relevance: nickel is a well known ferromagnet and silver has antibacterial properties. Both exist in the face centered cubic phase but are immiscible. In the context of alloys at the nanoscale, one can play with the size to fine tune a desired property, or to achieve new properties and functionalities that do not exist at the macroscopic regime. In this work, we explore how the subtle interaction between Ni and Ag triggers the chemical order, the electronic structure, and the magnetic properties of a AgNi nanoalloy of 55 atoms, a size that can accommodate core/shell configurations with sizable parts. Calculations are conducted within the density functional theory at the generalized gradient approximation for exchange and correlation. We determine, in the whole composition range, the chemical order, absolute and relative stabilities by means of binding energy, excess energy and second energy difference, as well as total and part-projected spin-polarized electronic densities of states and local charge and spin magnetic moments distribution. Ni-core/Ag-shell structures are particularly stable, but contrary to what one would expect by simply extrapolating the properties of the pure Ag and Ni clusters or of pure fcc bulks, we find unexpected behaviors along the composition range, such as quenched magnetic moments in Ni, total magnetic moments essentially contributed in some cases by Ag, or electronic charge transfer that changes its sign depending on the stoichiometry. These behaviors lead to magnetic transitions as a function of the composition, and differ, in some cases, from those of the smaller 13-atoms AgNi nanoalloys of the same symmetry with which we compare, a further demonstration of the complex nature of nanostructures. The above trends are robust against ionization and electron capture.

Measurement of the proton Zemach radius from the hyperfine splitting in muonic hydrogen atom

Muonic hydrogen is a bound state of a proton and a negative muon. Its Bohr radius is 200 times smaller than that of an electronic hydrogen atom. Therefore, a spectroscopy of the muonic hydrogen is highly sensitive to the finite size effect of proton. Recent years, the proton charge radius was determined by the laser spectroscopy of the Lamb shifts in muonic hydrogen atom. The experiment determined the proton charge radius significantly smaller than the results of past measurements. This anomaly is called “proton radius puzzle” and it has been an important unsolved problem in subatomic physics. Towards solving the puzzle, a new measurement of the ground-state hyperfine splitting in muonic hydrogen was proposed. The hyperfine splitting of muonic hydrogen derives the proton Zemach radius, which is defined as a convolution of the charge distribution with the magnetic moment distribution. This experiment aims to determine the proton Zemach radius with 1% precision by a measurement of the decay electron angular asymmetry. In order to test the feasibility of the laser spectroscopy, a preliminary experiment to measure the hyperfine quenching rate was proposed.

The Effect of Easy Axis Deviations on the Magnetization Reversal of Co Nanowire

Macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by 3-D model for Co nanowire with various easy axis deviations from applied field. It is found that both the coercivity and the remanence decrease monotonously with the increase of easy axis deviation as well as the maximum magnetic product, indicating the large impact of the easy axis orientation on the magnetic performance. Moreover, the calculated angular distributions and the evolution of magnetic moments have been shown to explain the magnetic reversal process. It is demonstrated that the large demagnetization field in the two ends of the nanowire makes the occurrence of reversal domain nucleation easier, hence the magnetic reversal. In addition, the magnetic reversal was illustrated in terms of the analysis of the energy evolution.

Tuning the magnetic properties of a ferrimagnet

Magnetic properties of manganese ferrite doped with lanthanum and gadolinium having compositional formula MnRExFe2−xO4 (where RE = La3+, Gd3+ and x = 0.02, 0.04, 0.06, 0.08, 0.10) synthesized by co-precipitation method have been investigated. The compositional variation of the magnetic properties for each rare earth ion was studied individually first. Then, the variation of the magnetic properties with the substitution of the two different ion having different magnetic moments was compared. Saturation magnetization of non-magnetic ion (La3+) substituted MnFe2O4 was found to be superior to that of magnetic ion (Gd3+) substituted MnFe2O4. The observed result was explained in terms of Neel’s theory of ferrimagnetism, distribution of cations and magnetic moment of the associated cations. Law of approach to saturation (LAS) was adopted to investigate the dependency of magnetization on the applied field. A strong dependence of magnetic property on the distribution of cations which is specific to the particular rare earth ion was revealed in the present study.

Energy of dendritic avalanches in thin-film superconductors

A method for calculating stored magnetic energy in a thin superconducting film based on quantitative magneto-optical imaging is developed. Energy and magnetic moment are determined with these calculations for full hysteresis loops in a thin film of the superconductor NbN. Huge losses in energy are observed when dendritic avalanches occur. Magnetic energy, magnetic moment, sheet current and magnetic flux distributions, all extracted from the same calibrated magneto-optical images, are analyzed and discussed. Dissipated energy and the loss in moment when dendritic avalanches occur are related to each other. Calculating these losses for specific spatially-resolved flux avalanches is a great advantage, because of their unpredictable and non-reproducible nature. The relative losses in energy are much higher than the relative losses in moment.

Magnetoresistance of epitaxial and polycrystalline Fe3O4 films near Verwey transition

We report investigations of magnetoresistance (MR) in epitaxial and polycrystalline Fe3O4 films. MR in epitaxial Fe3O4 films exhibits a local maximum at TV and a large value of −20% at 60 K. Based on a 1D half infinite spin chain model, the fitting parameter, which depends on the volume fraction of electronic scattering boundaries, sharply increases below TV with the decreased temperature. We suppose that the twin boundaries formed below TV facilitate the increase in MR and can act as antiphase boundaries (APBs) where the magnetic moments across twin boundaries are coupled antiferromagnetically. Similar MR behavior in Fe3O4(100) and (111) epitaxial films manifests the independence of MR on the spatial distribution of APBs. The outline of normalized MR in the epitaxial films shows a distinct temperature dependence. The temperature dependence may result from the different electronic transport mechanisms in Fe3O4 films. In a polycrystalline Fe3O4 film, MR comes from the disordered distribution of magnetic moments at grain boundaries. The effects of APBs, twin boundaries, and grain boundaries on MR are discussed in detail.

Complex Magnetization Harmonics of Polydispersive Magnetic Nanoclusters.

Understanding magnetic interparticle interactions within a single hydrodynamic volume of polydispersed magnetic nanoparticles and the resulting nonlinear magnetization properties is critical for their implementation in magnetic theranostics. However, in general, the field-dependent static and dynamic magnetization measurements may only highlight polydispersity effects including magnetic moment and size distributions. Therefore, as a complement to such typical analysis of hysteretic magnetization curves, we spectroscopically examined the complex magnetization harmonics of magnetic nanoclusters either dispersed in a liquid medium or immobilized by a hydrocolloid polymer, later to emphasize the harmonic characteristics for different core sizes. In the case of superparamagnetic nanoclusters with a 4-nm primary size, particularly, we correlated the negative quadrature components of the third-harmonic susceptibility with an insignificant cluster rotation induced by the oscillatory field. Moreover, the field-dependent in-phase components appear to be frequency-independent, suggesting a weak damping effect on the moment dynamics. The characteristic of the Néel time constant further supports this argument by showing a smaller dependence on the applied dc bias field, in comparison to that of larger cores. These findings show that the complex harmonic components of the magnetization are important attributes to the interacting cores of a magnetic nanocluster.