Local Magnetic Properties Research Articles

Monitoring the Local Structure and Magnetic Properties of the Dinuclear Cu2-Paddle Wheel Nodes in the Mesoporous Metal–Organic Framework, DUT-49(Cu), upon Adsorption-Induced Breathing Transitions

DUT-49(Cu) is a well-studied representative of flexible mesoporous frameworks, in particular, famous for long-lived overloaded metastable states in the presence of a variety of gases at defined temperatures, leading to “negative gas adsorption” transitions. Important mechanistic insights into these transitions in DUT-49 were obtained via in situ powder X-ray diffraction (PXRD) studies conducted in parallel to gas physisorption. However, for strongly X-ray absorbing probe molecules, such as xenon, such studies are not feasible, even if synchrotron radiation is used. Here we employ in situ electron paramagnetic resonance spectroscopy (EPR), PXRD, and adsorption isotherm measurements to explore the phase transformations in DUT-49(Cu) in the presence of xenon and compare its properties with the corresponding adsorption/desorption behavior of ethylene for this material. The antiferromagnetically coupled CuII–CuII dimers in the paddle-wheel (PW) units of this pillared layer MOF serve as local magnetic probes in the in situ EPR measurement. These experiments allowed us to monitor the op ↔ cp phase transformations during the xenon physisorption through the structural changes at the PW units encoded in the zero-field splitting parameters of the S = 1 state of the CuII dimers. The EPR data indicates an expansion of the unit cell for the cp phase in the presence of xenon. This novel EPR-derived insight into the phase transformation phenomena of the xenon-loaded DUT-49(Cu) could be validated by combined in situ EPR, PRXD, and adsorption isotherm measurements for ethylene adsorption over the same MOF material in a comparable temperature range.

Novel Insights of Enhanced Magnetization and Magnetoelectric Coupling in the Nanocomposite of BiFeO3 with Lanthanum Strontium Manganite

AbstractNovel insights on the magnetic, ferroelectric and magnetoelectric coupling of the nano composites of BiFeO3 (BFO) and La0.7Sr0.3Mn0.95Fe0.05O3 (LSMFO) with the latter exhibiting colossal magnetoresistance (CMR) behavior are provided in this study for the first time. Appreciable magnetoelectric coupling is observed in the composite and is seen to be significantly varying at temperatures below the blocking temperature of LSMFO. The local structure and magnetic properties of both the BFO and LSMFO particles in the composite are investigated in a detailed manner using Mössbauer spectroscopy studies specially devised to address the problem concerned. Enhanced values of the effective magnetic fields are observed at the Fe sites associated with BFO particles which are in contact with LSMFO particles. Interestingly, an appreciable increase in the magnetic hyperfine fields at Fe sites corresponding to LSMFO is also observed in the nanocomposites. New insights are derived based on the results of Mössbauer studies toward comprehending the magnetic and magnetoelectric coupling effects as deduced in these composites.

Density functional theory study of energetics, local chemical environment and magnetic properties in a high-entropic MnNiSi0.2Ge0.2Sn0.2Al0.2Ga0.2 intermetallic magnet

Rare-earth-free magnetostructural MnNiSi-based solid solutions are considered as promising candidates for solid-state cooling applications. In this paper, we use density functional theory calculations to study the energetics, variations in atomic displacements and bond length, and magnetic properties of high-entropic, intermetallic MnNi-X (X = Si0.2Ge0.2Sn0.2Al0.2Ga0.2) magnet in both the low-symmetry Pnma and high-symmetry structures, where we confine the large configurational entropy to the non-magnetic X-site of the compound. Our calculations reveal that the high-entropic chemical substitution of Si0.2Ge0.2Sn0.2Al0.2Ga0.2 in the X-site carry fingerprints that favor a reduction in magnetostructural transition temperature with minimal impact of total magnetization. These results motivate a promising path of high-entropic X-site substitutions to tune the magnetostructural properties of MnNiSi-based solid solutions.

Magnetic detection under high pressures using designed silicon vacancy centres in silicon carbide.

Pressure-induced magnetic phase transitions are attracting interest as a means to detect superconducting behaviour at high pressures in diamond anvil cells, but determining the local magnetic properties of samples is a challenge due to the small volumes of sample chambers. Optically detected magnetic resonance of nitrogen vacancy centres in diamond has recently been used for the in situ detection of pressure-induced phase transitions. However, owing to their four orientation axes and temperature-dependent zero-field splitting, interpreting these optically detected magnetic resonance spectra remains challenging. Here we study the optical and spin properties of implanted silicon vacancy defects in 4H-silicon carbide that exhibit single-axis and temperature-independent zero-field splitting. Using this technique, we observe the magnetic phase transition of Nd2Fe14B at about 7 GPa and map the critical temperature-pressure phase diagram of the superconductor YBa2Cu3O6.6. These results highlight the potential of silicon vacancy-based quantum sensors for in situ magnetic detection at high pressures.

Emergence of bond-dependent highly anisotropic magnetic interactions in Sr4RhO6 : A theoretical study

The quantum spin liquid states as a natural ground state of the Kitaev model has led to a quest for new materials candidates hosting Kitaev physics. Yet, there are very few material candidates in this category. Using a combination of $ab$ $initio$ and model Hamiltonian methods, we propose that Ruddlesden-Popper compound Sr$_4$RhO$_6$ belongs to this category. With a tight-binding model and exact diagonalization approach, we show that despite substantial trigonal-like distortion, the electronic and magnetic properties of Sr$_4$RhO$_6$ can be well described in terms of pseudo-spin = 1/2 states. Magnetic interactions among pseudo-spins, estimated using the second-order perturbation method are highly bond-dependent anisotropic in nature with two particularly noticeable features, antiferromagnetic Kitaev and Dzyaloshinskii-Moriya interactions. The gaped spin-wave spectra of Sr$_4$RhO$_6$ obtained with linear spin-wave theory is consistent with the underlying magnetic frustration. Additional analysis of the role of individual or a particular combination of magnetic interactions reveals that the spin-wave spectra of Sr$_4$RhO$_6$ is a combined effect of the highly anisotropic interactions and a relatively simpler minimal model may not be plausible in the current case. The crucial insights about coupling between the local structural features and magnetic properties of Sr$_4$RhO$_6$ obtained in this study may be helpful for future studies belonging to this class.

Thermally induced all-optical ferromagnetic resonance in thin YIG films

All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for the local detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert damping or spin stiffness. In this work we demonstrate that the AO-FMR method can be used in thin films of yttrium iron garnet (YIG) if a metallic capping layer (Au, Pt) is deposited on top of the film. Magnetization precession is triggered by heating of the metallic layer with femtosecond laser pulses. The heat pulse modifies the magneto-crystalline anisotropy of the YIG film and shifts the quasi-equilibrium orientation of the magnetization, which results in precessional magnetization dynamics. The laser-induced magnetization precession corresponds to a uniform (Kittel) magnon mode, with the precession frequency determined by the magnetic anisotropy of the material as well as the external magnetic field, and the damping time set by a Gilbert damping parameter. The AO-FMR method thus enables measuring local magnetic properties, with a resolution given by the laser spot size.

Local structure and magnetic properties of a nanocrystalline Mn-rich Cantor alloy thin film down to the atomic scale

The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multi-functionality. Herein, we apply multi-edge X-ray absorption spectroscopy (extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), and X-ray magnetic circular dichroism (XMCD)) to probe the structural, electronic, and magnetic properties of all individual constituents in the single-phase face-centered cubic (fcc)-structured nanocrystalline thin film of Cr20Mn26Fe18Co19Ni17 (at.%) high-entropy alloy on the local scale. The local crystallographic ordering and component-dependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature. A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances (2.54–2.55 Å) to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed. XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states, the changes in the electronic structure, and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film. The spin and orbital magnetic moments of Fe, Co, and Ni components were quantitatively evaluated. The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.

Magnetic properties deterioration of non-oriented steel due to laser cutting

In the manufacturing process of electrical machines, laser cutting is widely used to produce the laminations of cores. The internal stresses introduced by the high-energy laser beam will lead to deterioration in the magnetic properties of the non-oriented silicon steels. To accurately predict the core losses of the electrical machines, it is important to analyze the deterioration degree and the deterioration mechanism of the non-oriented steel sheets caused by laser cutting. In this paper, first, the local magnetic properties of the non-oriented steel 35WW250 at different positions are measured under the alternating sinusoidal excitation, in which the degradation degree is evaluated based on the core loss from the macroscopic perspective. Second, from the microscopic perspective, the observed magnetic domain patterns at the edge and those evolutions under the excitation of the magnetic field are investigated. The experimental results demonstrate that laser cutting can lead to the magnetic degradation of the non-oriented steels with a transverse depth of 18 mm from the edge. Moreover, the laser cutting process leads to significant variations in the patterns of the magnetic domains at different positions. The magneto-optical observation and local magnetic measurement verified the effectiveness of the analytical method, which is of great significance for the evaluation and improvement of the processing technique of the silicon steels.

Voltage control of frequency, effective damping, and threshold current in nano-constriction-based spin Hall nano-oscillators

Using micromagnetic simulations, we study the interplay between strongly voltage-controlled magnetic anisotropy (VCMA), ΔK=±200 kJ/m3, and gate width, w= 10–400 nm, in voltage-gated W/CoFeB/MgO based nano-constriction spin Hall nano-oscillators. The VCMA modifies the local magnetic properties such that the magnetodynamics transitions between regimes of (i) confinement, (ii) tuning, and (iii) separation with qualitatively different behaviors. We find that the strongest tuning is achieved for gate widths of the same size as the constriction width, for which the effective damping can be increased an order of magnitude compared to its intrinsic value. As a consequence, voltage control remains efficient over a very large frequency range, and subsequent manufacturing advances could allow spin Hall nano-oscillators to be easily integrated into next-generation electronics for further fundamental studies and industrial applications.

Probing the effect of Zn2+ on the local structure, dielectric and magnetic properties of La2CuMnO6 by solid state synthesis

The comparable ionic-radius cation substitution provides a route to investigate the origin of the physical properties of ceramics on the local structure and electronic charge state background. In analogy to our previous work [19] of La2CuMnO6 (LCM) prepared via solid-state route, here we are reporting the effect of Zn substitution at the Cu site of LCM. The detailed structural analysis confirmed the Jahn-Teller (JT) distortion in LCM and Zn2+ substituted LCM (i.e., LCZM) ceramics. Raman analysis further confirmed the JT distortion in these oxides. O K-edge and Mn K-edge XANES spectra confirmed the mixed hybridization states for Mn. A frequency-dependent relaxor state was observed in the dielectric study of LCM and LCZM. The dielectric responses of these systems are prominently driven by electron-phonon coupling. Their magnetic studies showed positive-Curie temperature (TC) and non-zero coercivity, indicating the ceramics' canted-antiferromagnetic nature.

Search for Magnetoelectric Coupling at the 57Fe/Hf0.5Zr0.5O2 Interface Using Operando Synchrotron Mössbauer Spectroscopy

AbstractMultiferroic materials with coexisting ferroelectric and ferromagnetic orders have attracted much attention due to the magnetoelectric coupling opening alternative prospects for electronic devices. Composite multiferroics containing separate ferroelectric and ferromagnetic components are a promising alternative to the single‐phase counterparts. Composite multiferroic structures comprising HfO2‐based ferroelectrics are potentially feasible for technological applications. Here, this study reports on the experiments aiming at the manifestation of magnetoelectric coupling at Fe/Hf0.5Zr0.5O2 (HZO) interface. Using synchrotron based 57Fe Mössbauer spectroscopy technique in operando, this study probes element‐selectively the local magnetic properties of a nanometer‐thick enriched 57Fe marker layer in functional Pt/57Fe/HZO/TiN capacitors and demonstrates the evidence of the ferroelectric polarization effect on the α‐Fe magnetic response. Besides α‐Fe exhibiting a magnetoelectric coupling, both ferromagnetic and superparamagnetic Fe3O4 components are found in the Mössbauer spectra, apparently originating from the oxygen or OH− ions penetrating ultrathin Pt overlayer during crystallization annealing of HZO. The observed effect as well as the electronic band lineup of the Fe/HZO interface elucidated from synchrotron based hard X‐ray photoemission spectroscopy measurements are interpreted in terms of charge‐mediated magnetoelectric coupling at the Fe/HfO2 interface driven by ferroelectric HZO polarization reversal.

X-ray Absorption Spectroscopy Study of Iron Site Manganese Substituted Yttrium Orthoferrite.

In this work, manganese (Mn)-doped YFeO3, i.e., YFMxO powders with 0 ≤ x ≤ 0.1, was synthesized by a hydrothermal method to study the influences of doping on its structural, morphological, optical, magnetic, and local electrical properties. The experimental results show that all the samples exhibit an orthorhombic structure with space group Pnma. Refined structure parameters are presented. Morphology images show the shape evolution from layered to multilayered with increasing Mn content. Infrared spectra reveal the characteristic vibrations of the obtained YFMxO samples. From the magnetic study, an increased magnetic moment in the range of 0 ≤ x ≤ 0.075 is observed. The Fe and Y K-edge local structure studies indicate that the valency of Fe and Y is mainly found in the trivalent state, which also indicates that the substitution of Mn ions not only affects the nearest neighbor atomic shell of Fe but also affects the nearest neighbor's local structure of Y atoms. Our results show that the addition of Mn exhibits an evident influence on the local structural and magnetic properties.

The Helicity Sign of Flux Transfer Event Flux Ropes and Its Relationship to the Guide Field and Hall Physics in Magnetic Reconnection at the Magnetopause

AbstractFlux Transfer Events (FTEs) are transient magnetic flux ropes typically found at the Earth's magnetopause on the dayside. While it is known that FTEs are generated by magnetic reconnection, it remains unclear how the details of magnetic reconnection controls their properties. A recent study showed that the helicity sign of FTEs positively correlates with the east‐west (By) component of the Interplanetary Magnetic Field (IMF). With data from the Cluster and Magnetospheric Multiscale missions, we performed a statistical study of 166 quasi force‐free FTEs. We focus on their helicity sign and possible association with upstream solar wind conditions and local magnetic reconnection properties. Using both in situ data and magnetic shear modeling, we find that FTEs whose helicity sign corresponds to the IMF By are associated with moderate magnetic shears while those that do not correspond to the IMF By are associated with higher magnetic shears. While uncertainty in IMF propagation to the magnetopause may lead to randomness in the determination of the flux rope core field and helicity, we rather propose that for small IMF By, which corresponds to high shear and low guide field, the Hall pattern of magnetic reconnection determines the FTE core field and helicity sign. In that context we explain how the temporal sequence of multiple X‐line formation and the reconnection rate are important in determining the flux rope helicity sign. This work highlights a fundamental connection between kinetic processes at work in magnetic reconnection and the macroscale structure of FTEs.

A deep learning model to discern indoor from outdoor environments based on data recorded by a tri-axial digital magnetic sensor

The increased use of wearable devices (WDs) for monitoring daily-life activities has led to the development of different location-driven applications. The first fundamental distinction is between indoor and outdoor environments. The most intuitive approach is the analysis of GPS coordinates or Wi-Fi signals [1] but both solutions are power consuming. In this study, we proposed and tested the use of deep learning techniques for indoor/outdoor discrimination based on local magnetic field properties of the specific environment during free-living activities. Eight participants were recruited in four different centres (Turin, Italy; Sheffield, UK; Newcastle upon Tyne, UK; Tel Aviv, Israel) and were equipped with the INDIP system [2] (including four magneto-inertial units attached to each foot, lower back, and non-dominant wrist), a smartphone (running the Aeqora mobile application) and were monitored during 2.5-hours of daily free-living activities. Magnetometer data was used to train a deep learning model, while indoor/outdoor probability based on GPS coordinates was provided by the Aeqora app and used as a reference. For each WD, the following features were extracted: x, y, z components and norm of the magnetometer and the 10-sample moving average (0.1 s window) of the latter features as a “contextual” rating. A bi-layer long short-term memory structure with a linear layer as a tail and with a gaussian error linear unit as activation unit has been implemented [3]. To achieve a lower-bias training and a more robust model, the network has been validated by exploiting a leave one subject out validation approach. In addition, the classification is based on two different observation timeframes: windows of length equal to the magnetometer data acquisition period (0.01 s) and 1 s windows. The average accuracy of the model, across participants, in the classification of indoor/outdoor environments while using as input one WD at a time and all WDs together is reported in Table 1. Based on this preliminary analysis, the model seems suitable for discerning indoor from outdoor environments with an average accuracy score higher than 88.3% in participants spread through three countries (different morphology of the territory, culture, lifestyle, etc.). With this respect, considering a longer observation time (1 s vs. 0.01 s) has resulted in increasing of the accuracy for all conditions. Overall, the best performances were obtained by using the whole INDIP system, with a 94.1% score. However, very similar performances were obtained when only one WD is considered. The effect of the experimental setup (e.g., the number and position of the WDs) and the input of the model (e.g., the length of the time-observation window) on the performance metrics require further investigations.

Wide field imaging of van der Waals ferromagnet Fe3GeTe2 by spin defects in hexagonal boron nitride

Emergent color centers with accessible spins hosted by van der Waals materials have attracted substantial interest in recent years due to their significant potential for implementing transformative quantum sensing technologies. Hexagonal boron nitride (hBN) is naturally relevant in this context due to its remarkable ease of integration into devices consisting of low-dimensional materials. Taking advantage of boron vacancy spin defects in hBN, we report nanoscale quantum imaging of low-dimensional ferromagnetism sustained in Fe3GeTe2/hBN van der Waals heterostructures. Exploiting spin relaxometry methods, we have further observed spatially varying magnetic fluctuations in the exfoliated Fe3GeTe2 flake, whose magnitude reaches a peak value around the Curie temperature. Our results demonstrate the capability of spin defects in hBN of investigating local magnetic properties of layered materials in an accessible and precise way, which can be extended readily to a broad range of miniaturized van der Waals heterostructure systems.

Localized magnetic properties measurement of interlocking core laminations

PurposeIn rotational alternating current machines, interlocking is a commonly used manufacturing method to fix laminated silicon steel cores. The purpose of this study is to measure the localized magnetic properties more comprehensively and to analyze the deteriorated magnetic properties caused by interlocking more accurately.Design/methodology/approachA movable B–H sensor is designed in this paper. The localized magnetic properties measurement was performed to investigate the magnetic properties around the interlocks with various sizes, various orientations and various numbers of laminations. Then, the damaged area caused by the interlocking was quantified, and the magnetic degradation of different degrees is layered.FindingsThe measurement results have shown that the interlocks with larger sizes, along the transverse direction and on 10-layer laminate, will lead to more serious magnetic degradation, and the maximum loss increment can reach up to 70%.Originality/valueThis work is an improvement and optimization based on the previous overall magnetic measurement of the interlock. The quantitative results of the localized magnetic measurement will have a certain significance for the accurate modeling and simulation of the electrical machines and provide valuable guidance for the optimization of the actual production process of the motor.

Punching effects on local magnetic properties near the edge of nonoriented electrical steels

PurposeThe purpose of this study is to investigate the effect of punching on the local magnetic properties of the nonoriented electrical steel sheet.Design/methodology/approachA microcomposite B–H sensor consisting of a pair of B probes with a spacing of 2 mm and a 1.8 × 1.8 mm2 H coil is designed. The region and degree of local magnetic properties degradation caused by punching can be quantitatively analyzed by flexibly moving the composite B–H sensor. The influence and physical mechanism of punching on the hysteresis loss, eddy current loss and excess loss are analyzed based on the Bertotti loss separation theory.FindingsThis study investigates the deterioration effect of the punched nonoriented electrical steel. The permeability near the edge decreases, and the core loss as well as the microhardness increases. The region of magnetic property deterioration is dependent on the area of work hardening.Originality/valueThe microcomposite B–H sensor can be used to measure the magnetic properties near the edge of electrical steel sheets under different processing conditions. This study provides the possibility of precise magnetic property model of the motor core after punching, especially valuable for motors without annealing process.

Local imaging of diamagnetism in proximity-coupled niobium nanoisland arrays on gold thin films

In this work we study the effect of engineered disorder on the local magnetic response of proximity coupled superconducting island arrays by comparing scanning Superconducting Quantum Interference Device (SQUID) susceptibility measurements to a model in which we treat the system as a network of one-dimensional (1D) superconductor-normal metal-superconductor (SNS) Josephson junctions, each with a Josephson coupling energy $E_J$ determined by the junction length or distance between islands. We find that the disordered arrays exhibit a spatially inhomogeneous diamagnetic response which, for low local applied magnetic fields, is well described by this junction network model, and we discuss these results as they relate to inhomogeneous two-dimensional (2D) superconductors. Our model of the static magnetic response of the arrays does not fully capture the onset of nonlinearity and dissipation with increasing applied field, as these effects are associated with vortex motion due to the dynamic nature of the scanning SQUID susceptometry measurement. This work demonstrates a model 2D superconducting system with engineered disorder and highlights the impact of dissipation on the local magnetic properties of 2D superconductors and Josephson junction arrays.

Growth of Fe-doped and V-doped MoS2 and their magnetic-electrical effects

Magnetism in two-dimensional (2D) materials has attracted much attention recently. However, intrinsic magnetic 2D materials are rare and mostly unstable in ambient. Although heteroatom doping can introduce magnetism, the basic property especially the electrical-magnetic coupling property has been rarely revealed. Herein, both iron (Fe)-doped and vanadium (V)-doped MoS2 films were grown by chemical vapor deposition. Through studying the structure and electrical property of Fe-doped and V-doped MoS2, it was found that both Fe and V doping would decrease the electron concentration, exhibiting a p-type doping effect. Significantly, V-doped MoS2 displays a p-type conduction behavior. Although the carrier mobility decreases after heteroatom doping, both Fe and V doping could endow MoS2 with magnetism, in which the transfer curves of both MoS2 transistors exhibit a strong magnetic-dependent behavior. It is found that the magnetic response of Fe-doped MoS2 can be tuned from ~0.2 ​nA/T to ~1.3 ​nA/T, with the tunability much larger than that of V-doped MoS2. At last, the magnetic mechanism is discussed with the local magnetic property performed by magnetic force microscopy. The typical morphology-independent magnetic signal demonstrates the formed magnetic domain structure in Fe-doped MoS2. This study opens new potential to design novel magnetic-electrical devices.

Quantum Imaging of Magnetic Phase Transitions and Spin Fluctuations in Intrinsic Magnetic Topological Nanoflakes.

Topological materials featuring exotic band structures, unconventional current flow patterns, and emergent organizing principles offer attractive platforms for the development of next-generation transformative quantum electronic technologies. The family of MnBi2Te4 (Bi2Te3)n materials is naturally relevant in this context due to their nontrivial band topology, tunable magnetism, and recently discovered extraordinary quantum transport behaviors. Despite numerous pioneering studies to date, the local magnetic properties of MnBi2Te4 (Bi2Te3)n remain an open question, hindering a comprehensive understanding of their fundamental material properties. Exploiting nitrogen-vacancy (NV) centers in diamond, we report nanoscale quantum imaging of the magnetic phase transitions and spin fluctuations in exfoliated MnBi4Te7 flakes, revealing the underlying spin transport physics and magnetic domains at the nanoscale. Our results highlight the unique advantage of NV centers in exploring the magnetic properties of emergent quantum materials, opening new opportunities for investigating the interplay between topology and magnetism.