Direction Of Magnetic Moment Research Articles

Quantitative Analysis of the Measurable Areas of Differential Magnetic Gradient Tensor Systems for Unexploded Ordnance Detection

Achieving effective detection of unexploded ordnance (UXO) is of great significance for ensuring the safety of human lives and regional economic development. Differential magnetic tensor gradient systems have strong application prospects for UXO detection because of their low orientation requirements and exceptional sensitivity to weak magnetic fields. These systems usually have a hollow ring-shaped measurable range, referred to as the “measurable area”. With the rapid advancement of the tensor measurement system, it is necessary to further analyse the measurable area performance. In this paper, a simulation method based on a target magnetic dipole revolving around such a measurement system is designed for evaluating the measurable area. An improved Frobenius norm is adopted to compare the measured tensor data, and the centre distance is used instead of the baseline distance to better describe the scale of the measurement system. The measurable areas of planar cross-shaped, square, and triangular structures are studied, as well as the corresponding influencing factors. Finally, the quantitative relationships between the measurable area performance of the three structures and the magnetic dipole moment direction, the sensor accuracy, and the centre distance of the measurement system are obtained.

Probing magnetic configuration-mediated topological phases via high harmonic generation in MnBi2Te4

Compared to a space group, a magnetic space group is much more complex, as both magnetic structure and magnetic moment direction can change the original symmetries of materials. The interplay between space symmetry and magnetism can generate versatile novel quantum states. However, detecting these topological phases experimentally, achieved through manipulating the magnetic configuration, has been restricted. It is mainly because the intrinsic link between the theory and the available experimental technique remains elusive. Here, we show that high harmonic generation (HHG) can identify these topological quantum states. We use rhombohedral ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ film as an example, and analyze the symmetry-dependent harmonic order and signal by combining first-principles calculations and time-dependent Liouville equation numerical computations. Our results provide a fundamental basis for using HHG to study the topological quantum phases mediated by various magnetic configurations that can be easily realized by applying an external magnetic field.

2.2]Paracyclophane-Based Chiral Platforms for Circularly Polarized Luminescence Fluorophores and Their Chiroptical Properties: Past and Future.

Quality of CPL fluorophore is defined by the vectors of electric dipole transition moment and imaginary magnetic dipole transition moment. The aim of this review is to introduce readers to a chiral moiety applicable to CPL studies focusing on chiral cyclophanes because the rigid cyclophanes are able to hold the vector directions of electric dipole transition moment and imaginary magnetic dipole transition moment.

Magnetic structures, spin-flop transition, and coupling of Eu and Mn magnetism in the Dirac semimetal EuMnBi2

We report here a comprehensive study of the AFM structures of the Eu and Mn magnetic sublattices as well as the interplay between Eu and Mn magnetism in this compound by using both polarized and non-polarized single-crystal neutron diffraction. Magnetic susceptibility, specific heat capacity measurements and the temperature dependence of magnetic diffractions suggest that the AFM ordering temperature of the Eu and Mn moments is at 22 and 337 K, respectively. The magnetic moments of both Eu and Mn ions are oriented along the crystallographic $c$ axis, and the respective magnetic propagation vector is $\textbf{k}_{Eu} = (0,0,1)$ and $\textbf{k}_{Mn}=(0,0,0)$. With proper neutron absorption correction, the ordered moments are refined at 3 K as 7.7(1) $\mu_B$ and 4.1(1) $\mu_B$ for the Eu and Mn ions, respectively. In addition, a spin-flop (SF) phase transition of the Eu moments in an applied magnetic field along the $c$ axis was confirmed to take place at a critical field of B$_c$ $\sim$ 5.3 T. The evolution of the Eu magnetic moment direction as a function of the applied magnetic field in the SF phase was also determined. Clear kinks in both field and temperature dependence of the magnetic reflections ($\pm1$, 0, 1) of Mn were observed at the onset of the SF phase transition and the AFM order of the Eu moments, respectively. This unambiguously indicates the existence of a strong coupling between Eu and Mn magnetism. The interplay between two magnetic sublattices could bring new possibilities to tune Dirac fermions via changing magnetic structures by applied fields in this class of magnetic topological semimetals.

Measurement of Far Field Magnetic Moment Vector of a Moving Ferromagnetic Object

In magnetic anomaly detection, it is a prerequisite to master the far-field magnetic moment vector information of the target. It is important to measure the magnetic moment of the target in target location, recognition and degaussing. In the paper, we proposed a method of measuring the magnetic moment vector of the target based on the total geomagnetic field. In this method, a sensor array with the scalar magnetometers was constructed and the quantitative factors of the magnetometer were analyzed. In order to eliminate the time-varying and uneven spatial distribution of geomagnetic total field, a double gradient algorithm was applied to magnetic moment measurement in this method. And a criterion function of determining the magnitude and direction of the target magnetic moment was defined. The proposed method was validated by the theoretical calculation and real experimental data. The results showed that the measured magnetic field data were qualitatively in good agreement with the theoretical curve. For the magnitude of magnetic moment, the average relative deviation was 5.1%. And the average relative deviation of inclination and declination of the moment were 3.2% and 2.5%, respectively. In addition, we attempted to separate the induced magnetic moment and the intrinsic magnetic moment of the target. The proposed method can be used as a reference for the target magnetic location and demagnetization.

Magnetization reorientation induced by spin–orbit torque in YIG/Pt bilayers* *Project supported by the Natural Science Foundation of Shaanxi Province, China (Grant No. 2020JM-088), the National Natural Science Foundation of China (Grant Nos. 51572222, 51701158, and 51872241), and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 3102017jc01001 and 310201911cx044).

In this work, we report the reorientation of magnetization by spin–orbit torque (SOT) in YIG/Pt bilayers. The SOT is investigated by measuring the spin Hall magnetoresistance (SMR), which is highly sensitive to the direction of magnetic moment of YIG. An external in-plane rotating magnetic field which is applied to the YIG/Pt bilayers, and the evolutions of SMR under different injected currents in the Pt layer, result in deviation of SMR curve from the standard shape. We conclude that the SOT caused by spin accumulation near the interface between YIG and Pt can effectively reorient the in-plane magnetic moment of YIG. This discovery provides an effective way to modulate YIG magnetic moments by electrical methods.

Synthesis and magnetic properties of chromium doped cobalt ferrite nanotubes

Chromium (Cr) doped cobalt ferrite (Co1−xCrxFe2O4:x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.1, denoted as to CCFO) hollow nanotubes were synthesized by electrospinnig method followed by, calcining treatment at 700 °C in air. The samples exhibited a single phase cubic spinel phase. The lattice constant of the samples was found to initially decreased and thereafter increases with increased of Cr content. The morphology analysis indicated that the samples displayed a disordered arrangements of hollow structures and the relevant surfaces were rough and porous. Transmission electron microscopy (TEM) paragraph confirmed that the doped CCFO nanotubes had a polycrystalline nature and exhibited the changes in the corresponding crystal structure. X-ray photoelectron spectroscopy (XPS) confirmed that Cr doping affect the crystal structure and atomic-binding energy. The analysis of magnetic hysteresis loop indicated an obvious reduction in the saturation magnetization (Ms) of cobalt ferrite with increasing in Cr substitution. The remanent magnetization (Mr) and coercivity were increased at first and then decreased with increasing of Cr content, which was elucidated by the surface effect and magnetic moment direction. The switching field distribution analysis indicated the magnetically crystal soft phase and there were multiple-step processes to reach magnetic reversal.

Noncoplanar ferrimagnetism and local crystalline-electric-field anisotropy in the quasicrystal approximant Au70Si17Tb13

Neutron scattering experiments have been performed to elucidate magnetic properties of the quasicrystal approximant Au70Si17Tb13, consisting of icosahedral spin clusters in a body-centered-cubic lattice. Bulk magnetic measurements performed on the single crystalline sample unambiguously confirm long-range ordering at T C = 11.6 ± 1 K. In contrast to the simple ferromagnetic response in the bulk measurements, single crystal neutron diffraction confirms a formation of intriguing non-collinear and non-coplanar magnetic order. The magnetic moment direction was found to be nearly tangential to the icosahedral cluster surface in the local mirror plane, which is quite similar to that recently found in the antiferromagnetic quasicrystal approximant Au72Al14Tb14. Inelastic neutron scattering on the powdered sample exhibits a very broad peak centered at ℏω ≃ 4 meV. The observed inelastic spectrum was explained by the crystalline-electric-field model taking account of the chemical disorder at the fractional Au/Si sites. The resulting averaged anisotropy axis for the crystalline-electric-field ground state is consistent with the ordered moment direction determined in the magnetic structure analysis, confirming that the non-coplanar magnetic order is stabilized by the local uniaxial anisotropy.

Stoner-Wohlfarth switching of the condensate magnetization in a dipolar spinor gas and the metrology of excitation damping

We consider quasi-one-dimensional dipolar spinor Bose-Einstein condensates in the homogeneous-local-spin-orientation approximation, that is with unidirectional local magnetization. By analytically calculating the exact effective dipole-dipole interaction, we derive a Landau-Lifshitz-Gilbert equation for the dissipative condensate magnetization dynamics, and show how it leads to the Stoner-Wohlfarth model of a uni-axial ferro-magnetic particle, where the latter model determines the stable magnetization patterns and hysteresis curves for switching between them. For an external magnetic field pointing along the axial, long direction, we analytically solve the Landau-Lifshitz-Gilbert equation. The solution explicitly demonstrates that the magnetic dipole-dipole interaction {\it accelerates} the dissipative dynamics of the magnetic moment distribution and the associated dephasing of the magnetic moment direction. Under suitable conditions, dephasing of the magnetization direction due to dipole-dipole interactions occurs within time scales up to two orders of magnitude smaller than the lifetime of currently experimentally realized dipolar spinor condensates, e.g., produced with the large magnetic-dipole-moment atoms ${}^{166} \textrm{Er}$. This enables experimental access to the dissipation parameter $\Gamma$ in the Gross-Pitaevski\v\i~mean-field equation, for a system currently lacking a complete quantum kinetic treatment of dissipative processes and, in particular, an experimental check of the commonly used assumption that $\Gamma$ is a single scalar independent of spin indices.

Description of the Colossal Magnetoresistance of La1.2Sr1.8Mn2O7 Based on the Spin-Polaron Conduction Mechanism in the Ferromagnetic Temperature Range

We have analyzed the resistance of La1.2Sr1.8Mn2(1 – z)O7 single crystal in magnetic fields from 0 to 90 kOe in the ferromagnetic temperature range. The observed magnetoresistance of La1.2Sr1.8Mn2O7 is described based on the spin-polaron conduction mechanism. The magnetoresistance is determined by the change in the sizes and magnetic moment directions of magnetic inhomogeneities (polarons). It is shown that the colossal magnetoresistance is ensured by an increase (along the magnetic field) of the polaron linear size. It is found using the method for separating the contributions of different conduction mechanisms to the magnetoresistance that the contribution to the magnetoresistance from the orientation mechanism at 80 K in low magnetic fields is close to 50%. With increasing magnetic field, this contribution decreases and becomes small in fields exceeding 30 kOe. The comparable contributions to the conductivity from the orientational and spin-polaron mechanisms unambiguously necessitate the inclusion of both conduction mechanisms in the magnetoresistance calculations. We have calculated the temperature variation of the polaron size (in relative units) in zero magnetic field and in a magnetic field of 90 kOe.

Reservoir computing with two-bit input task using dipole-coupled nanomagnet array

Reservoir computing (RC), which utilizes physical phenomena, is a candidate for low energy consumption recurrent neural networks. Recently, we proposed RC which uses a dipole-coupled nanomagnet array as a reservoir, which applies the direction of the static magnetic moment of each nanomagnet as a node state in the array. It is possible to learn binary tasks with one-bit input data using this reservoir. Moreover, more complex tasks such as motion detection utilize multi-bit input data. This study simulates a two-bit binary input RC by employing the dipole coupled nanomagnet array as a reservoir. We apply a binary task with two-bit input data, which requires a memory capacity and non-linear computing capability of the reservoir. Due to the simulations with a macrospin model at a temperature of 0 K, this RC was able to learn these binary tasks by utilizing 24 nanomagnets.

Magnetoelastic anisotropy of antiferromagnetic materials

Antiferromagnetic (AFM) materials are of great interest for spintronics. Here, we report the magnetoelastic anisotropy of an AFM IrMn thin film. An exchange-biased CoFeB/IrMn bilayer was used to obtain a single domain of the AFM thin film, and the magnetic moment arrangement of the AFM layer was deduced from the magnetic hysteresis loop of the pinned FM layer. A uniaxial compressive stress is applied on the thin film through changing the temperature due to the anisotropic thermal expansion of the polyvinylidene fluoride (PVDF) substrate. Both experimental results and theoretical calculations show that the direction of IrMn magnetic moment can be changed when a compressive stress is applied and the direction of IrMn AFM moment rotates about 10° under 2.26 GPa compressive stress. These results provide important information for the practical application of flexible spintronics based on AFM spintronic devices.

Band gap control of bilayer zigzag graphene nanoribbon by direction of magnetic moment

We have demonstrated the first-principles calculation to tune the band gap of the bilayer zigzag graphene nanoribbon by arranging the direction of the magnetic moments of carbon atoms at the edges. These directions were specified by the polar angle, as defined in the spherical coordinates. From the ferromagnetic configuration to the antiferromagnetic configuration, as the polar angle increases, the band gap increases. We also showed that the ferromagnetic configuration leads to the metallic system while the others lead to the insulator, in a good agreement with the previous calculations. These results indicated that the bilayer zigzag graphene nanoribbon is potential for the spintronics devices.

Tunable magnetism of a single-carbon vacancy in graphene

Creating a single-carbon vacancy introduces (quasi-)localized states for both σ and π electrons in graphene. Theoretically, interactions between the localized σ electrons and quasilocalized π electrons of a single-carbon vacancy in graphene are predicted to control its magnetism. However, experimentally confirming this prediction through manipulating the interactions remains an outstanding challenge. Here we report the manipulation of magnetism in the vicinity of an individual single-carbon vacancy in graphene by using a scanning tunnelling microscopy (STM) tip. Our spin-polarized STM measurements, complemented by density functional theory calculations, indicate that the interactions between the localized σ and quasilocalized π electrons could split the π electrons into two states with opposite spins even when they are well above the Fermi level. Via the STM tip, we successfully manipulate both the magnitude and direction of magnetic moment of the π electrons with respect to that of the σ electrons. Three different magnetic states of the single-carbon vacancy, exhibiting magnetic moments of about 1.6 μB, 0.5 μB, and 0 μB respectively, are realized in our experiment.

Orbital Magnetic Moments in Strained SrRuO3 Thin Films

We carried out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy and evaluated orbital magnetic moments in compressively strained tetragonal and tensilely strained monoclinic SrRuO3 epitaxial thin films whose magnetic easy axis directions and behavior of the transverse resistivity differ from each other. We found that regardless of the types of the strain, SrRuO3 films have negative orbital magnetic moments arranged antiparallel to the spin magnetic moments along the magnetic easy axis directions. The magnitudes of the orbital moments for both films are similar: ∼−0.17 μB/Ru at 20 K. These observations indicate that the films’ structures tie only to the direction of the orbital magnetic moments and consequently determine the magnetic easy axis direction in SrRuO3 through the strong magnetocrystalline effect. This highlights the significance of the orbital magnetic moment as a factor determining of the magnetic anisotropy of this oxide. Our results provide important physical insight into magnetic and magneto-transport properties of SrRuO3.

A self-biased linear anisotropic magnetoresistance sensor realized by exchange biased bilayers

A ferromagnetic/antiferromagnetic (FM/AFM) bilayers structure was proposed to act as a new structure to meet the demands of anisotropic magnetoresistance (AMR) linear sensor. Through a single domain model, we found that the direction of initial magnetic moment of FM layer could be modulated by the co-effect of the exchange bias (EB) field along vertical direction and the shape anisotropy field induced by limited regular size magnetic thin film. When the length and width of magnetic thin film are fixed, if a proper magnitude of EB field is adopted, the 45-degree self-biased AMR sensor can be achieved, and vice versa. Following the model, a series of Ta/NiFe/FeMn/Ta samples were grown by changing the EB field and shape anisotropy field, the self-biased sensor cell with high linearity and sensitivity was achieved.

Magnetic property and cation distributions in boron-doped MFe2O4(M = Ni, Mn) spinel ferrites

(A)[B]2O4 spinel ferrites with initial compositions, BxM1−xFe2O4 (M = Ni or Mn), were prepared using the solid state reaction technique. X-ray photoelectron spectra indicate that there were only 25% of boron ions in the end samples while the remaining boron ions were lost in the thermal treatment process. Therefore, the end samples have a composition of Bx1Mx2Fe3−x1−x2O4 (M = Ni or Mn). X-ray diffraction patterns showed that the end samples possess a single-phase cubic spinel structure. For the two series of samples, the observed dependencies on the boron content, x1, of the sample magnetic moments at 10 K were fitted successfully by using the quantum mechanical potential barrier model. The cation distributions were obtained in the fitting process, during which the magnetic moment direction of the Mn3+ cations was assumed to anti-ferromagnetically couple with those of other cations whenever they are at the (A) or [B] sites in the samples, according to the O 2p itinerant electron model.

Study of Magnetic Properties of Fe100-xNix Nanostructures Using the Mössbauer Spectroscopy Method.

Hyperfine interactions of 57Fe nuclei in Fe100-xNix nanostructures synthesized in polymer ion-track membranes were studied by Mössbauer spectroscopy. The main part of obtained nanostructures was Fe100-xNix nanotubes with bcc structure for 0 ≤ x ≤ 40, and with fcc structure for 50 ≤ x ≤ 90. The length, outside diameter and wall thickness of nanotubes were 12 μm, 400 ± 10 nm and 120 ± 5 nm respectively. For the studied nanotubes a magnetic texture is observedalong their axis. The average value of the angle between the direction of the Fe atom magnetic moment and the nanotubes axis decreases with increasing of Ni concentration for nanotubes with bcc structure from ~50° to ~40°, and with fcc structure from ~55° to ~46°. The concentration dependences of the hyperfine parameters of nanotubes Mössbauer spectra are qualitatively consistent with the data for bulk polycrystalline samples. With Ni concentration increasing the average value of the hyperfine magnetic field increases from ~328 kOe to ~335 kOe for the bcc structure and drops to ~303 kOe in the transition to the fcc structure and then decreases to ~290 kOe at x = 90. Replacing the Fe atom with the Ni atom in the nearest environment of Fe atom within nanotubes with bcc structure lead to an increase in the hyperfine magnetic field by “6–9 kOe”, and in tubes with fcc structure—to a decrease in the hyperfine magnetic field by “11–16 kOe”. The changes of the quadrupole shift and hyperfine magnetic field are linearly correlated with the coefficient −(15 ± 5)·10−4 mm/s/kOe.

Nanocrystallization and Recoilless Fraction Determination of Fe68.5Co5Nb3Cu1Si15.5B7 Ferromagnetic Alloy

Amorphous alloy Fe68.5Co5Nb3Cu1Si15.5B7 was obtained by melt spinning. Samples cut from the foil were annealed at 450, 550, 650 and 750°C in a vacuum furnace. 57Fe Mossbauer spectroscopy was used to identify the crystalline phases formed and the orientation of the magnetic moments based on the refined values of the hyperfine parameters. The spectra of the samples annealed at 550, 650 and 750°C were indicative of nanocrystallization, with the magnetic moments reoriented out-of-plane for the last sample. This behavior is in contradistinction to that of the Co-rich system, which was totally crystallized at these annealing temperatures. Our results show that small Co additions can lead to the formation of nanostructures over a whole range of annealing temperatures. A new series of Mossbauer spectra was obtained by recording simultaneously the intensity transmitted by a superposition of the sample with the stainless steel etalon, based on the dual absorber method previously introduced by us. The values of the recoilless fraction could be derived from the relative spectral areas. The f factor maintained values close to 0.7 for all samples measured, but dropped to 0.37 for the sample annealed at 750°C. This behavior could be related to the presence of elastic stresses in the system, which caused the out-of-plane reorientation of the magnetic moment directions.

Magnetism in α-RuCl3: Dependence on Coulomb Interaction and Hund’s Coupling

Employing the density functional theory, we have investigated the roles of Coulomb and Hund’s interactions in the electronic and magnetic properties of newly discovered α-RuCl3 having the R $$\overline 3 $$ symmetry, which is in close proximity of the Kitaev system. We show that both the size and the direction of local magnetic moment are highly dependent on Coulomb and Hund’s interactions, and the spin and orbital parts show different behaviors. The validity of the so-called jeff picture is accessed upon interaction parameters, and the explicit roles of Hund’s interaction in the local electronic structures and magnetic properties are discussed.