Types Of Magnetic Structures Research Articles

Tailoring the Magnetic, Structural and Shielding Characteristics of Nano Er2O3 via Ni Doping

We investigated the effects of Ni-doping amount on the structural, magnetic, and shielding properties of nano Er2O3. Nano Er2−xNixO3 (x = 0, 0.05, 0.1, 0.15) samples were fabricated by a pechini scheme and characterized via X-ray diffraction. Rietveld refinement was used to discover the distribution of cations on the two crystallographic sites. Cation ordering in the two nonequivalent sites of the structure and the variation of the oxygen bond lengths of octahedra with the composition x were also investigated. A consistent reduction in the average bond lengths of (Er/Ni)O6 octahedra around 8b and 24d as x progresses was observed. Average crystallite size reduced while average lattice micro-strain increased with increasing Ni doping. The correlation between magnetization and temperature for all samples under a magnetic field of 200 Oe was studied. Curie-Weiss law was applied to find the magnetic moments and the types of magnetic structure. The μ eff in the Er2−xNixO3 samples dropped from 9.7 to 9.36 μB as the nickel doping level rose from 0 to 0.15. Calculated magnetic moments, μ cal, were found to drop from 9.4 to 9.02 μB as the nickel doping level changed from x = 0 to x = 0.15 in Er2−xNixO3 samples. Curie paramagnetic temperature (θ) for all samples has been observed to rise from −10.6 to −19.34. The theoretical gamma-ray attenuation parameters for nano Er2−xNixO3 samples were acquired through the Phy-X/PSD software. The nano Er2−xNixO3 samples have been proven to possess remarkable magnetic and neutron shielding applications.

Large off-diagonal magnetoelectricity in a triangular Co2+-based collinear antiferromagnet

Magnetic toroidicity is an uncommon type of magnetic structure in solid-state materials. Here, we experimentally demonstrate that collinear spins in a material with R-3 lattice symmetry can host a significant magnetic toroidicity, even parallel to the ordered spins. Taking advantage of a single crystal sample of CoTe6O13 with an R-3 space group and a Co2+ triangular sublattice, temperature-dependent magnetic, thermodynamic, and neutron diffraction results reveal A-type antiferromagnetic order below 19.5 K, with magnetic point group -3′ and k = (0,0,0). Our symmetry analysis suggests that the missing mirror symmetry in the lattice could lead to the local spin canting for a toroidal moment along the c axis. Experimentally, we observe a large off-diagonal magnetoelectric coefficient of 41.2 ps/m that evidences the magnetic toroidicity. In addition, the paramagnetic state exhibits a large effective moment per Co2+, indicating that the magnetic moment in CoTe6O13 has a significant orbital contribution. CoTe6O13 embodies an excellent opportunity for the study of next-generation functional magnetoelectric materials.

Statistical Characteristics of Electron Vortexes in the Terrestrial Magnetosheath

Utilizing the unprecedented high-resolution Magnetospheric Multiscale mission data from 2015 September to 2017 December, we perform a statistical study of electron vortexes in the turbulent terrestrial magnetosheath. On the whole, 506 electron vortex events are successfully selected. Electron vortexes can occur at four known types of magnetic structures, including 78, 42, 26, and 39 electron vortexes observed during the crossings of the current sheets, magnetic holes, magnetic peaks, and flux ropes, respectively. Except for the four types of structures, the rest of the electron vortexes are in the “Others” category, defined as unknown structures. The electron vortexes mainly occur in the subsolar region, with only a few in the flank region. The total occurrence rate of all electron vortexes is 4.86 hr–1, with, on average, 3.65 events hr−1 in the X-Y plane and 3.26 events hr−1 in the X-Z plane. The durations of most of the electron vortexes concentrate within 0.5–1.5 s and are 1.09 s on average. The electron vortexes are ion-scale structures owing to the average scale of 2.05 ion gyroradius. In addition, the means, medians, and maxima of the energy dissipation J · E′ in the electron vortexes are almost positive, implying that the electron vortex may be a potential coherent structure or channel for turbulent energy dissipation. All these results reveal the statistical characteristics of electron vortexes in the magnetosheath and improve our understanding of energy dissipation in astrophysical and space plasmas.

Magnetite @ Zinc Cobalt Ferrite Nanoparticles: Synthesis, Magnetic Behavior, and Optical Properties

One of the main challenges is using an effective photocatalyst that responds to a broad range of visible light for hydrogen production during water splitting. Series types of photocatalysts based on magnetic ferrite nanostructure were fabricated via a two-step co-precipitation technique. Precisely, four types of magnetic structures: magnetite nanoparticles (MNPs), zinc cobalt ferrite nanoparticles (ZCFNPs), hybrid magnetite/zinc cobalt ferrite nanoparticles (MNPs @ ZCFNPs), and hybrid zinc cobalt ferrite/magnetite nanoparticles (ZCFNPs @ MNPs) were used to fabricate magnetic photocatalysts. The characterizations of the fabricated magnetic photocatalysts were investigated via TEM, zeta potential, XRD, VSM, and UV–VIS spectroscopy. ZCFNPs @ MNPs showed the smallest particle with size ≈11 nm. The magnetization value of ZCFNPs @ MNPs (59.3 emu/g) was improved compared to the MNPs (41.93 emu/g). The produced hydrogen levels via photocatalyst were 60, 10, 24, and 1.4 mmole min−1 g−1 for MNPs, ZCFNPs, MNPs @ ZCFNPs, and ZCFNPs @ MNPs, respectively, under visible light with magnetic force. MNPs displayed outstanding performance as magnetic photocatalysts for the water-splitting process.

Complete X-ray census of M dwarfs in the solar neighborhood

Context. X-ray emission is the most sensitive diagnostic of magnetic activity in M dwarfs and, hence, of the dynamo in low-mass stars. Moreover it is crucial for quantifying the influence of the stellar irradiation on the evolution of planet atmospheres. Aims. We have embarked in a systematic study of the X-ray emission in a volume-limited sample of M dwarf stars to explore the full range of activity levels present in their coronae. We look to obtain a better understanding of the conditions in their outer atmospheres and their possible impact on the circumstellar environment. Methods. Based on a recent catalog of Gaia objects within 10 pc from the Sun, we identified all its stars with spectral types between M0 and M4 and we carried out a systematic search for X-ray measurements of this sample. To this end, we used both archival data from ROSAT, XMM-Newton, and the ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission, as well as our own dedicated XMM-Newton observations. To make inferences on the properties of the M dwarf corona, we compared the range of their observed X-ray emission levels to the flux radiated by the Sun from different types of magnetic structures: coronal holes, background corona, active regions, and cores of active regions. In this work, we focus on the properties of stars with the faintest X-ray emission. Results. At the current state of our project, with more than 90% of the 10 pc M dwarf sample observed in the X-ray, there is only one star that has had no detections: GJ 745 A. With an upper limit luminosity of log Lx (erg s−1) < 25.4 and an X-ray surface flux of log FX,SURF (erg cm−2 s−1) < 3.6, GJ 745 A defines the lower boundary of the X-ray emission level for M dwarfs. Together with its proper motion companion (GJ 745 B), it is the only star in this volume-complete sample located in the range of X-ray surface flux that corresponds to the faintest solar coronal structures, namely: coronal holes. The fact that the ultra-low X-ray emission level of GJ 745 B (log Lx (erg s−1) = 25.6 and log FX,SURF (erg cm−2 s−1) = 3.8) is entirely attributed to flaring activity indicates that while its corona is dominated by “holes,” at least one magnetically active structure is present. This structure determines the total X-ray brightness and the coronal temperature of the star.

Magnetic ordering and chirality in multiferroic Dy1-xHoxMnO3 (x = 0.2)

Effect of substitution Dy by Ho on the magneto-electric behavior of the compound Dy0.8Ho0.2MnO3 was investigated by the different methods of polarized and classical neutron diffraction and macroscopic methods. It is shown that substitution by Ho of 20% on the position of Dy do not change overall crystal symmetry of compound. It remains of Pbnm type down to the very low temperatures. Magnetic ordering, its temperature and field evolution was determined by the use of single crystal neutron diffraction and magnetization measurements. Chiral type of magnetic structure on Mn subsystem is confirmed below Tc ≈ 16 K. Using polarized neutron diffraction the 3-component character of rare earth magnetic ordering in Dy0.8Ho0.2MnO3 in contrast to DyMnO3 could be revealed. It was shown that doping by 20% Ho suppresses the spontaneous rare-earth ordering with its own propagation vector and provides the situation when two magnetic subsystems, manganese and rare earth ones have a coherent incommensurate spatial propagation. The influence of the external electric field on the magnetic chirality could be directly evidenced, proving strong magneto-electric coupling in multiferroic phase. The study of the electric polarization under similar temperatures and fields on the same samples provides the direct correlation between the results of the microscopic and macroscopic investigations.

Brillouin Light Scattering from Magnetic Excitations.

Brillouin light scattering (BLS) has been established as a standard technique to study thermally excited sound waves with frequencies up to ~100 GHz in transparent materials. In BLS experiments, one usually uses a Fabry-Pérot interferometer (FPI) as a spectrometer. The drastic improvement of the FPI contrast factor over 1010 by the development of the multipass type and the tandem multipass type FPIs opened a gateway to investigate low energy excitations (ħω ≤ 1 meV) in various research fields of condensed matter physics, including surface acoustic waves and spin waves from opaque surfaces. Over the last four decades, the BLS technique has been successfully applied to study collective spin waves (SWs) in various types of magnetic structures including thin films, ultrathin films, multilayers, superlattices, and artificially arranged dots and wires using high-contrast FPIs. Now, the BLS technique has been fully established as a unique and powerful technique not only for determination of the basic magnetic constants, including the gyromagnetic ratio, the magnetic anisotropy constants, the magnetization, the SW stiffness constant, and other features of various magnetic materials and structures, but also for investigations into coupling phenomena and surface and interface phenomena in artificial magnetic structures. BLS investigations on the Fe/Cr multilayers, which exhibit ferromagnetic-antiferromagnetic arrangements of the adjacent Fe layer's magnetizations depending on the Cr layer's thickness, played an important role to open the new field known as "spintronics" through the discovery of the giant magnetoresistance (GMR) effect. In this review, I briefly surveyed the historical development of SW studies using the BLS technique and theoretical background, and I concentrated our BLS SW studies performed at Tohoku University and Ishinomaki Senshu University over the last thirty five years. In addition to the ferromagnetic SW studies, the BLS technique can be also applied to investigations of high-frequency magnetization dynamics in superparamagnetic (SPM) nanogranular films in the frequency domain above 10 GHz. One can excite dipole-coupled SPM excitations under external magnetic fields and observe them via the BLS technique. The external field strength determines the SPM excitations' frequencies. By performing a numerical analysis of the BLS spectrum as a function of the external magnetic field and temperature, one can investigate the high-frequency magnetization dynamics in the SPM state and determine the magnetization relaxation parameters.

Prominence fine structures in weakly twisted and highly twisted magnetic flux ropes

Context. Many prominences are supported by magnetic flux ropes. One important question is how we can determine whether the flux rope is weakly twisted or highly twisted. Aims. In this paper, we attempt to decipher whether prominences supported by weakly twisted and highly twisted flux ropes can manifest different features so that we might distinguish the two types of magnetic structures based on their appearance. Methods. We performed pseudo three-dimensional simulations of two magnetic flux ropes with different twists. Results. We find that the resulting two prominences differ in many aspects. The prominence supported by a weakly twisted flux rope is composed mainly of transient threads (∼82.8%), forming high-speed flows inside the prominence, and its horns are evident. Conversely, the prominence supported by a highly twisted flux rope consists mainly of stable quasi-stationary threads (∼60.6%), including longer independently trapped threads and shorter magnetically connected threads. Our simulations also reveal that the prominence spine deviates from the flux rope axis in the vertical direction and from the photospheric polarity inversion line projected on the solar surface, especially for the weakly twisted magnetic flux rope. Conclusions. The two types of prominences differ significantly in appearance. Our results also suggest that a piling-up of short threads in highly twisted flux ropes might account for the vertical-like threads in some prominences.

Slow spin dynamics and quantum tunneling of magnetization in the dipolar antiferromagnet DyScO3

We present a comprehensive study of static and dynamic magnetic properties in the Ising-like dipolar antiferromagnet (AFM) DyScO$_3$\ by means of DC and AC magnetization measurements supported by classical Monte-Carlo calculations. Our AC-susceptibility data show that the magnetic dynamics exhibit a clear crossover from an Arrhenius-like regime to quantum tunneling of magnetization (QTM) at $T^* = 10$ K. Below $T_{\mathrm{N}} = 3.2$ K DyScO$_3$ orders in an antiferromagnetic $GxAy$-type magnetic structure and the magnetization dynamics slow down to the minute timescale. The low-temperature magnetization curves exhibit complex hysteretic behavior, which depends strongly on the magnetic field sweep rate. We demonstrate that the low-field anomalies on the magnetization curve are related to the metamagnetic transition, while the hysteresis at higher fields is induced by a strong magnetocaloric effect. Our theoretical calculations, which take into account dipolar interaction between Dy$^{3+}$ moments, reproduce essential features of the magnetic behavior of DyScO$_3$. We demonstrate that DyScO$_3$ represents a rare example of inorganic compound, which exhibits QTM at a single-ion level and magnetic order due to classical dipolar interaction.

Electron-scale Magnetic Peaks Upstream of the Terrestrial Bow Shock Observed by the Magnetospheric Multiscale Mission

Abstract The solar wind has rich wave activity and various magnetic structures. Here we report on a new type of magnetic structure in the solar wind using the unprecedented high temporal resolution data from the Magnetospheric Multiscale Mission. We find that a train of magnetic peaks with a size less than 1 ion inertial length exists upstream of the terrestrial bow shock. The electron number density and the perpendicular electron temperature have a slight decrease inside the magnetic peaks, leading to a decrease of the electron thermal pressure in the structure. These structures are pressure-balanced, and they are approximately stationary in the ambient electron flow. These electron-scale magnetic peaks are identified as magnetic bottle–like, and their cross sections are roughly circular. The electron velocity has a bipolar feature relative to the ambient flow in the cross section, indicating the existence of an electron vortex. The current density is mainly contributed by electrons. The peaks occur in a marginally mirror-stable environment; thus they are not locally generated by mirror instabilities. We suggest that the origin of the electron vortex might help to shed light on the formation of electron-scale magnetic peaks in the solar wind.

Magnetic and magneto-thermal properties of ferrimagnetic alloys (Er1−x Y x )(Co0.84Fe0.16)2 and their dependence on the orientations of resultant and sublattice magnetizations

In this paper structure, magnetic and magneto-thermal properties: magnetic entropy change (ΔS m) and refrigeration capacity (q) of Er1–x Y x (Co0.84Fe0.16)2 alloys (x = 0, 0.2, 0.4, 0.6, 0.8, 1) in magnetic fields up to 90 kOe in a temperature range of 5–360 K are investigated. An analysis of temperature dependences of magnetization (σ) and high-field susceptibility (χ hf) showed that in these compounds, three different ferri- and a one ferromagnetic structures are consequently realized. Concentration dependences of magnetic moment at 5 K (μ f.u.), Curie temperature (T C), residual magnetization (σ r) and coercivity (H c) have been shown to have an extreme at intermediate Y concentration. The character of temperature dependence of magnetic entropy change (ΔS m(T)) depends on the composition and originates from the type of magnetic structure of the compound and the mutual orientation of R- and 3d- element sublattices magnetization with respect to the resulting one. In compounds with x = 0.6 and x = 0.8 temperature regions with different signs of ΔS m are observed, reflecting the change of dominating R- or 3d- sublattice in the resulting magnetization.

Magnetic ordering of Ho and its role in the magnetization reversal and coercivity double peaks in the Ho3Fe5O12 garnet

Rare-earth based garnet system, Ho3Fe5O12 shows magnetization compensation phenomenon at Tcomp = 138 K and a magnetic transition at 50 K. In the present work, we reveal the physics of these low temperature magnetic transitions by carrying out detailed dc magnetization, ac susceptibility, neutron depolarization, and neutron diffraction studies. Interestingly, our dc magnetization study under low (≲ 50 Oe) magnetic fields has shown a previously unknown sign reversal of magnetization (below the Tcomp) that persists down to 5 K, the lowest measured temperature. Magnetic measurements under moderate fields between 50 Oe and 1 kOe reveal two compensation temperatures (in the range of 105 – 150 K depending upon the applied field value) leading to double magnetization reversals. Interestingly, for magnetic fields ≥ 1 kOe, these two compensation temperatures merge to a single Tcomp (=138 K). A modified Stoner-Wohlfarth model has been used to explain the asymmetrical nature of double peak around the Tcomp in the temperature dependent coercivity data. The ac susceptibility study supports the existence of both the transitions with an evidence of deep minimum at the Tcomp (138 K) and a broad peak at 50 K. Mesoscopic neutron depolarization study has revealed a zero domain-magnetization state at the Tcomp. Temperature dependent neutron diffraction study has revealed that Ho carries an induced moment above the Tcomp due to polarizing effect under the internal magnetic field of the two magnetically ordered Fe sublattices at 567 K, whereas a single umbrella type ordering of Ho sublattice moments appears below the Tcomp, resulting in the distortion of magnetic unit cell from cubic to rhombohedral symmetry. However, below 50 K, Ho3+ sites are divided into two inequivalent magnetic sublattices, having different moments and canting angles, and it leads to double umbrella type magnetic structure. Neutron diffraction study has revealed an asymmetric variation of the tetrahedral, octahedral, and dodecahedral sublattice moments resulting in a magnetization reversal at ~ 138 K which is very well supported by the mean field theory calculations. In the present study, we have resolved the ambiguity of magnetic ordering of the rare-earth (Ho3+) sublattice and its role in multiple magnetic transitions. The utility of such compensated ferrimagnetic materials in spin polarizers/analyzers and fast switching memory devices has been emphasized.

Resonances of the Faraday Effect in Nanostructured Iron Garnet Films

Magnetic nanostructures make it possible to enhance magneto-optical effects by many times owing to the excitation of optical resonances. A new type of magnetic structure is proposed, which is a two-dimensional all-dielectric bismuth-substituted iron garnet grating. Enhancement of the Faraday effect in such a structure caused by the excitation of waveguide modes is described analytically, and the conditions for the resonant enhancement are revealed. The resonant enhancement of the Faraday effect in all-dielectric magnetic nanostructures has been experimentally demonstrated for the first time.

Magnetism and its coexistence with superconductivity in CaK(Fe0.949Ni0.051)4As4 : Muon spin rotation/relaxation studies

The magnetic response of CaK(Fe$_{0.949}$Ni$_{0.051}$)$_4$As$_4$ was investigated by means of the muon-spin rotation/relaxation. The long-range commensurate magnetic order sets in below the N\'{e}el temperature $T_{\rm N}= 50.0(5)$~K. The density-functional theory calculations have identified three possible muon stopping sites. The experimental data were found to be consistent with only one type of magnetic structure, namely, the long-range magnetic spin-vortex-crystal order with the hedgehog motif within the $ab-$plane and the antiferromagnetic stacking along the $c-$direction. The value of the ordered magnetic moment at $T\approx3$ K was estimated to be $m_{\rm Fe}=0.38(11)$ $\mu_{\rm B}$ ($\mu_{\rm B}$ is the Bohr magneton). A microscopic coexistence of magnetic and superconducting phases accompanied by a reduction of the magnetic order parameter below the superconducting transition temperature $T_{\rm c}\simeq 9$ K is observed. Comparison with 11, 122, and 1144 families of Fe-based pnictides points to existence of correlation between the reduction of the magnetic order parameter at $T\rightarrow 0$ and the ratio of the transition temperatures $T_{\rm c}/T_{\rm N}$. Such correlations were found to be described by Machida's model for coexistence of itinerant spin-density wave magnetism and superconductivity [Machida, J. Phys. Soc. Jpn. 50, 2195 (1981) and Bud'ko et al., Phys. Rev. B 98, 144520 (2018)].

New type of magnetic structure in the R2T2X group: Tb2Pd2In

Anisotropy of bulk magnetic properties and magnetic structure studies of a Tb2Pd2In single crystal by means of bulk magnetization methods and neutron diffraction techniques confirmed the antiferromagnetic order below the Néel temperature 29.5 K. The collinear magnetic structure of Tb magnetic moments aligned along the tetragonal c-axis is characterized by a propagation vector k = (1/4, 1/4, 1/2), yielding an equal-moment structure with alternating coupling between nearest as well as next-nearest Tb neighbors within the basal plane and antiferromagnetic coupling between the c-axis neighbors. In the context of magnetism of R2T2X compounds, where R stands for rare-earth or actinide element, such collinear structure with long-wavelength periodicity represents a new type of magnetic structure.

An X-ray activity cycle on the young solar-like star ɛ Eridani

Chromospheric Ca II activity cycles are frequently found in late-type stars, but no systematic programs have been created to search for their coronal X-ray counterparts. The typical time scale of Ca II activity cycles ranges from years to decades. Therefore, long-lasting missions are needed to detect the coronal counterparts. The XMM-Newton satellite has so far detected X-ray cycles in five stars. A particularly intriguing question is at what age (and at what activity level) X-ray cycles set in. To this end, in 2015 we started the X-ray monitoring of the young solar-like star ɛ Eridani, previously observed on two occasions: in 2003 and in early 2015, both by XMM-Newton. With an age of 440 Myr, it is one of the youngest solar-like stars with a known chromospheric Ca II cycle. We collected the most recent Mount Wilson S-index data available for ɛ Eridani, starting from 2002, including previously unpublished data. We found that the Ca II cycle lasts 2.92 ± 0.02 yr, in agreement with past results. From the long-term XMM-Newton lightcurve, we find clear and systematic X-ray variability of our target, consistent with the chromospheric Ca II cycle. The average X-ray luminosity is 2 × 1028erg s−1, with an amplitude that is only a factor of 2 throughout the cycle. We apply a new method to describe the evolution of the coronal emission measure distribution of ɛ Eridani in terms of solar magnetic structures: active regions, cores of active regions, and flares covering the stellar surface at varying filling fractions. Combinations of these three types of magnetic structures can only describe the observed X-ray emission measure of ɛ Eridani if the solar flare emission measure distribution is restricted to events in the decay phase. The interpretation is that flares in the corona of ɛ Eridani last longer than their solar counterparts. We ascribe this to the lower metallicity of ɛ Eridani. Our analysis also revealed that the X-ray cycle of ɛ Eridani is strongly dominated by cores of active regions. The coverage fraction of cores throughout the cycle changes by the same factor as the X-ray luminosity. The maxima of the cycle are characterized by a high percentage of covering fraction of the flares, consistent with the fact that flaring events are seen in the corresponding short-term X-ray lightcurves predominately at the cycle maxima. The high X-ray emission throughout the cycle of ɛ Eridani is thus explained by the high percentage of magnetic structures on its surface.

Direct control of magnetic chirality in NdMn2O5 by external electric field

Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroic NdMn2O5 has been performed using both non-polarized and polarized neutron diffraction techniques. Below TN = 30.5 K magnetic Bragg reflections corresponding to the non-chiral type magnetic structure with propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted magnetic modulation with a similar vector kz2 occurs, which is attributed to the magnetization of the Nd3+ ions by the Mn-sub-lattice. Strong temperature hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5 was observed depending on the cooling or heating history of the sample. Below about 20 K the magnetic structure became of a chiral type. From spherical neutron polarimetry measurements, the resulting low-temperature magnetic structure kz3 was approximated by the general elliptic helix. The parameters of the magnetic helix-like ellipticity and helical plane orientation in regard to the crystal structure were determined. A reorientation of the helix occurs at an intermediate temperature between 4 K and 18 K. A difference between the population of right- and left-handed chiral domains of about 0.2 was observed in the as-grown crystal when cooling without an external electric field. The magnetic chiral ratio can be changed by the application of an external electric field of a few kV/cm, revealing strong magnetoelectric coupling. A linear dependence of the magnetic chirality on the applied electric field in NdMn2O5 was found. The results are discussed within the frame of the antisymmetric super-exchange model for Dzyaloshinsky-Moria interaction.

Особенности импульсного перемагничивания высококоэрцитивного материала на основе наночастиц ε-Fe-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

The magnetic structure of the polymorphic modification of iron oxide ε-Fe2O3 is collinear ferrimagnetic in the range from room temperature to ~ 150 K. Further, with decreasing a temperature in ε-Fe2O3, a magnetic transition occurs, accompanied by a significant decrease in the coercive force HC, and in the low temperature range ε-Fe2O3 is characterized by a complex incommensurate magnetic structure. In this work, we experimentally investigated the processes of dynamic magnetization reversal of ε-Fe2O3 nanoparticles of an average size of 8 nm in the temperature range of 80–300 K, comprising various types of magnetic structure of this iron oxide. A bulk material was studied - xerogel SiO2 with ε Fe2O3 nanoparticles embedded in pores. To measure the magnetic hysteresis loops under dynamic magnetization reversal, a pulsed magnetic field technique of Hmax up to 130 kOe was used, using the method of discharging a capacitor bank through a solenoid. The coercive force of HC during dynamic magnetization reversal noticeably exceeds HC for quasi-static conditions. This is caused by processes of superparamagnetic relaxation of the magnetic moments of particles during pulsed magnetization reversal. In the range from room temperature to ~ 150 K, the rate of change of the external field dH / dt is the main parameter determining the behavior of the coercive force under the conditions of dynamic magnetization reversal. This behavior is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K), when the magnetic structure of ε Fe2O3 is incommensurate, the coercive force during pulsed magnetization reversal already depends on the parameter dH / dt, and is largely determined by the maximum applied field Hmax. Such a behavior, atypical for systems of ferrimagnetic particles, is already caused by dynamic spin processes inside ε-Fe2O3 particles during fast magnetization reversal.

Formation of an Antiferromagnetic Metal Phase in the Electron-Doped Sr0.98La0.02MnO3 Oxide According to 17O NMR Data

The spin density distribution of itinerant electrons, neg, and their effect on pairwise correlations of localized spins S(t2g) of Mn4+ ions in cubic Sr1 − xLaxMnO3 antiferromagnet (x = 0.02, TN = 230 K, G type magnetic structure) is studied experimentally by nuclear magnetic resonance on 17O nuclei. The regions with neg > x, in which the local spin susceptibility of pairs of Mn atoms follows the dependence χ ∼ (T − Θ)−1 with Θ = 20(5) K, indicating the growth of ferromagnetic spin correlations of neighboring magnetic ions in these domains, are found in the paramagnetic phase. The fraction of Mn-O-Mn bonds (neg > x) increases with the decrease in the temperature. The interpenetrating meshes of Mn-O-Mn bonds with different densities of itinerant eg electrons form an antiferromagnetic metal phase below TN. The role of weak localization effects is discussed as the main origin of the magnetic inhomogeneity of the antiferromagnetic metal phase in Sr0.98La0.02MnO3.

Magnetic Field MEMS-Sensor: Functional Characteristics Control during the Formation of Magnetosensitive Structures

In this work the results of substrate temperature effects on coercivity and magnetoresistance in ferromagnetic structures are shown. It was found that with an increase of the substrate temperature from 270 to 390 °C the magnetoresistance increases from 1.2 to 2.3% and the coercive force from 1.6 to 5.3 Oe. A new topology of anisotropic magnetoresistive structures is proposed. In these structures the shape of ferromagnetic elements repeats the shape of nonmagnetic conducting shunts. Sensitivity values obtained for both types of magnetic structures are compared.