Dependence Of Hysteresis Loops Research Articles

Tuning of magnetic bistability and domain wall dynamics in magnetic microwires

A unique combination of unusual magnetic properties, such as magnetic bistability associated with ultrafast domain wall propagation or ultrasoft magnetic properties, together with excellent mechanical and corrosion properties can be obtained in amorphous microwires. Such ferromagnetic microwires coated with insulating and flexible glass-coating with diameters ranging from 0.1 to 100 can be prepared using the Taylor-Ulitovsky method. Magnetic properties of glass-coated microwires are affected by chemical compositions of the metallic nucleus and can be substantially modified by post-processing. We provide an overview of the routes allowing tuning of hysteresis loops and domain wall dynamics in amorphous microwires and new experimental results on the dependence of hysteresis loops on external stimuli, such as applied stress and temperature.

Exchange Bias Effect of Ni@(NiO,Ni(OH)2) Core/Shell Nanowires Synthesized by Electrochemical Deposition in Nanoporous Alumina Membranes.

Tuning and controlling the magnetic properties of nanomaterials is crucial to implement new and reliable technologies based on magnetic hyperthermia, spintronics, or sensors, among others. Despite variations in the alloy composition as well as the realization of several post material fabrication treatments, magnetic heterostructures as ferromagnetic/antiferromagnetic coupled layers have been widely used to modify or generate unidirectional magnetic anisotropies. In this work, a pure electrochemical approach has been used to fabricate core (FM)/shell (AFM) Ni@(NiO,Ni(OH)2) nanowire arrays, avoiding thermal oxidation procedures incompatible with integrative semiconductor technologies. Besides the morphology and compositional characterization of these core/shell nanowires, their peculiar magnetic properties have been studied by temperature dependent (isothermal) hysteresis loops, thermomagnetic curves and FORC analysis, revealing the existence of two different effects derived from Ni nanowires' surface oxidation over the magnetic performance of the array. First of all, a magnetic hardening of the nanowires along the parallel direction of the applied magnetic field with respect their long axis (easy magnetization axis) has been found. The increase in coercivity, as an effect of surface oxidation, has been observed to be around 17% (43%) at 300 K (50 K). On the other hand, an increasing exchange bias effect on decreasing temperature has been encountered when field cooling (3T) the oxidized Ni@(NiO,Ni(OH)2) nanowires below 100 K along their parallel lengths.

Magnetic Behavior of Ising Nanowire with Mixed Integer Spins: A Monte Carlo Study

The magnetic and thermal properties of a ferrimagnetic mixed spin-1 and spin-2 cubic Ising nanowire are studied by using the Monte Carlo simulation. The influences of the nearest (JAB) and next-nearest neighbor (JA and JB) exchange interactions and the single-ion anisotropies (DA and DB) on the critical and compensation temperatures are illustrated. Moreover, the phase diagrams on the (temperature, anisotropy) plane are plotted for several values of JA/|JAB|. The system shows very rich and interesting behaviors, namely first and second order phase transitions, tricritical points and compensation phenomenon. Finally, the dependence of hysteresis loops on the anisotropies, the exchange interactions and the temperature is also investigated.

Temperature Dependent Electrical and Electrocaloric Properties of Textured 0.72PMN - 0.28PT Ceramics*

Lead magnesium niobate (PMN) - lead titanate (PT) solid solution ceramics in the ratio of 0.72PMN-0.28PT was produced by a combination of tape-casting in ⟨001⟩pc textured and random forms. The Lotgering factor, f, of textured ceramics was approximately calculated as 80%. Modified Curie-Weiss analysis indicated relaxor dominant behavior for both the random and textured ceramics. Development of texture led to an enhancement in the electromechanical properties with converse piezoelectric charge coefficient (d33*) under 20 kV/cm electric field reaching 545 pm/V for the textured ceramic. Electrocaloric (EC) behavior of random and textured ceramics were obtained from indirect measurements using temperature dependent polarization vs. electric field hysteresis loops. An EC temperature change (ΔTEC) of ∼0.5 K was calculated from the PMN-28PT ceramics at around 80 °C under an electric field of 60 kV/cm. Development of texture was demonstrated to have led to an anisotropy in the EC response.

INFLUENCE OF SURFACE ROUGHNESS ON THE DYNAMIC STALL OF A ROTARY WING SECTION IN SUBSONIC FLOW

Wear involves the losses of some material from the surface and leads to the surface roughness. In the present work, the influence of surface roughness on the dynamic stall of a rotary wing section in subsonic flow has been investigated with different degree of surface roughness. The airfoil surface roughness was estimated using arithmetic mean roughness value (ISO-4287/1). For this purpose an indicial response method for unsteady, two dimensional flow is used to calculating the unsteady lift and pitching moment of NACA 0012 airfoil undergoing a pitching oscillation in the deep dynamic stall regime. Using the ANSYS-5.8 software as a source for the preliminary static data that required by the indicial method. The investigation is done through a number of test cases with different mean angles of attack, amplitude and reduced frequencies for airfoil oscillating around its quarter chord axis. The results include the time dependent behaviour and hysteresis loops of the lift and pitching moment for the airfoil with different degree of surface roughness. For rough airfoil an aerodynamic characteristic showed a reduction in the lift coefficient, separation point moved forward to the leading edge, the boundary layer reattachment take place at smaller angle of attack, the stall angle decrease and the pitching moment coefficient decrease as compared with smoother airfoil. So the periodic test must be done and re-coating the rotary wing if the surface roughness increased.

Front Cover: An Iron(II) Spin Crossover Complex with a Maleonitrile Schiff base‐like Ligand and Scan Rate‐dependent Hysteresis above Room Temperature (Z. Anorg. Allg. Chem. 8/2021)

The cover picture shows a scan-rate dependent thermal hysteresis loop for an iron(II) spin crossover complex. Intermolecular interactions between the iron centres, illustrated as dashed lines in the packing diagram, are responsible for the observation of bistability of the high spin and the low spin state, but also for kinetic effects. A faster scan rate leads to an apparent wider hysteresis loop, thus very slow measurements are necessary to correctly determine the spin crossover properties of the material. More details can be found in the Article by Birgit Weber et al.

All chemical solution deposition of epitaxial porous BiFe0.93Mn0.07O3 thin films

BiFeO3 as a type of single-phase room temperature multiferroic materials has aroused intensive investigations in recent years. Construction of porous BiFeO3 thin films is helpful for integration of other materials with desirable functionalities. Here, epitaxial BiFe0.93Mn0.07O3 (001) thin films were prepared on SrRuO3-buffered LaAlO3 (001) single crystal substrates by an all-solution chemical solution deposition, which is beneficial for large area thin film fabrication with low cost. Through addition of F-127 copolymer into the precursor solution, pores can be effectively introduced in BiFe0.93Mn0.07O3 (001) thin films while the epitaxy can be maintained. The amount of pores is gradually increased with increasing of the F-127 addition. The leakage current density is not obviously changed and the conduction mechanism can be well fitted through Ohmic behavior. Electric field dependent polarization hysteresis loops can be effectively maintained and the room temperature magnetic moment is obviously improved with the introduction of pores in epitaxial BiFe0.93Mn0.07O3 (001) thin films. The results will provide a facile route to fabricate large area epitaxial porous BiFeO3 thin films as an effective template for integration of other materials to realize desirable functionalities.

A new universal mutator circuit for memcapacitor and meminductor elements

In this work, a CBTA-based universal mutator circuit is proposed for the realization of memcapacitor and meminductor elements. Proposed mutator circuit contains only one CBTA element, one memristor and one capacitor. It is suitable to transform a grounded memristor to a floating memcapacitor or meminductor. SPICE simulation by using a CBTA designed with 0.18 μm level-7 TSMC CMOS transistors was performed to show the accuracy of the proposed circuit and as a result, frequency dependent hysteresis loops are obtained.

Composition dependent ferro-piezo hysteresis loops and energy density properties of mechanically activated (Pb1−xLax)(Zr0.60Ti0.40)O3 ceramics

In the present study, ferroelectric and piezoelectric nature of La substituted lead zirconate titanate was investigated to decide the optimum La content. (Pb1−xLax)(Zr0.60Ti0.40)O3 (hereinafter PLZT x/60/40) ceramics were synthesized using novel processing approach of high energy ball milling and cold isostatic pressing (CIP). This study deals with two types of hysteresis loops, polarization (P–E) and strain vs. electric field (S–E) loops. Energy density properties, remanent polarization (Pr), coercive field (Ec), piezoelectric charge coefficient (d33), internal macroscopic electric field (Ein), domain switching current (Imax) and strain hysteresis, normalized strain coefficient (Smax/Emax) were also calculated to study the behaviour of PLZT x/60/40 ferroelectrics. In addition, current vs. electric field (I–E) curves were traced not only to support P–E studies and determination of the Ec but also to confirm the ferroelectricity and domain switching characteristics studies. The PLZT 8/60/40 electro-ceramics not only show the highest Pr ~ 29.1 μC/cm2, Imax ~ 2 mA, unipolar strain ~ 0.25% and average d33 ~ 632 pm/V but also the lowest Ec ~ 9.4 kV/cm and strain hysteresis loss ~ 4%.

Energy storage properties in SrTiO3–Bi3.25La0.75Ti3O12 thin films

Ferroelectric thin films with slim electric field dependent polarization hysteresis loops, showing small remnant polarization and large polarization, are desired to obtain high recoverable energy density and efficiency for ferroelectric capacitors in energy storage performance. Here, SrTiO3 alloying effects on Bi3.25La0.75Ti3O12 thin films are prepared by sol-gel method and the energy storage performance have been investigated. With increasing the Bi3.25La0.75Ti3O12 content, the crystalline quality and grain size are increased as well as the improvement in polarization. Slim electric field dependent hysteresis loops can be obtained when the Bi3.25La0.75Ti3O12 content is higher than 0.6. The optimized composition is 0.4SrTiO3-0.6Bi3.25La0.75Ti3O12 thin film with the recoverable energy density and high efficiency of 44.7 J/cm3 and 87.4%, respectively. Moreover, the 0.4SrTiO3-0.6Bi3.25La0.75Ti3O12 thin film shows excellent energy storage performance in wide frequency range, fatigue endurance and thermal stability. The results suggest that energy storage performance in Bi3.25La0.75Ti3O12 thin films can be effectively improved through SrTiO3 alloying, and can be considered as candidates for dielectric energy storage capacitors.

Role of film thickness on magnetic properties of sputter deposited Co2FeGa alloy thin films

We report the role of film thickness on the structure, microstructure and magnetic properties of Co2FeGa thin films. The grain size was observed to increase with increase in film thickness. An in-plane magnetic anisotropy was observed for all the films. A gradual increase in saturation magnetization (Ms) and a nearly constant coercivity (Hc) was observed in the films with thickness >10 nm at room temperature. Curie temperature (TC) was found to increase gradually with increase in film thickness which is attributed to the increase in grain size with the film thickness. Thermal stability of the films was studied from the temperature dependent magnetic hysteresis loops which exhibit nearly a constant value of Ms till 873 K for all the films. This evidences the high temperature stability of Co2FeGa thin films. The increase in Hc at higher temperatures is attributed to the diffusion of Si into the film.

Evidence of compositional fluctuation induced relaxor antiferroelectric to antiferroelectric ordering in Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 based lead free ferroelectric

The high temperature electrical phase transitions of (1 − x) Bi0.5Na0.5TiO3–(x) Bi0.5K0.5TiO3 (x = 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35) relaxor ferroelectrics have been investigated by employing the dielectric spectroscopy technique. The Rietveld refinement of the XRD patterns reveals the increase of the lattice distortion (c/a) from 1.001 to 1.006 in the tetragonal crystal symmetry (P4mm) with the increase of the BKT (x = 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35) mole fraction. The different bonds vibration (Bi3+/Na+/K+–O and Ti4+–O) related to phonon modes have been studied by analyzing the Raman spectra. The relaxor antiferroelectric ordering temperature (Td: depolarization temperature) of Bi0.5Na0.5TiO3 (BNT) reduce from ~ 200 to ~ 91 °C with the increase of the BKT mole fraction. This observation is well correlated to the formation of polar nanoregions (PNRs) due to the compositional fluctuation in the local crystal structure. Also, Td varies with the frequency of the applied electric. It suggests the presence of the PNRs and, subsequently exhibits the relaxor ferroelectric behavior. The activation energy to activate the PNRs reduces from 2.573 to 2.383 meV with the increase of the BKT mole fraction in the solid solutions. Reduction in remanent electrical polarization and the electrical coercive field in temperature dependent ferroelectric hysteresis loops suggest the relaxor antiferroelectric behavior of the solid solutions (x ≥ 0.15) near the depolarization temperature.

Direct Photoluminescence Probing of Ferromagnetism in Monolayer Two-Dimensional CrBr3.

Atomically thin magnets are the key element to build up spintronics based on two-dimensional materials. The surface nature of two-dimensional ferromagnet opens up opportunities to improve the device performance efficiently. Here, we report the intrinsic ferromagnetism in atomically thin monolayer CrBr3, directly probed by polarization resolved magneto-photoluminescence. The spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature of 34 K. The development of magnons by the thermal excitation is in line with the spin-wave theory. We attribute the layer-number-dependent hysteresis loops in thick layers to the magnetic domain structures. As a stable monolayer material in air, CrBr3 provides a convenient platform for fundamental physics and pushes the potential applications of the two-dimensional ferromagnetism.

Dynamical effects of memristive load on peak current mode buck-boost switching converter

Abstract When an output load of switching DC-DC converter exhibits the fingerprints of frequency dependent pinched hysteresis loops, the load can be regarded as a memristive load. By substituting a resistive load with the voltage-controlled memristive load emulator, a peak current mode (PCM) memristive buck-boost converter is presented in this paper. Based on the circuit equations under two kinds of switch states, the switched conditions and normalized system model of the PCM memristive buck-boost converter operating at continuous conduction mode (CCM) are derived. Through MATLAB numerical plots, dynamical behaviors of the PCM memristive buck-boost converter are investigated and dynamical effects of the memristive load on the buck-boost converter are thereby uncovered. The results indicate that such a buck-boost converter exhibits complex dynamical behaviors including chaos, period, period-doubling bifurcation, and border collision bifurcation; the memristive load does not affect the bifurcation structures but can make the normal operation region to broaden and cause the average output voltages to drop. Additionally, the enlargement of the memristive effect of the load, the normal operation regions are further expanded and the average output voltages are further reduced. Finally, PSIM simulation model is constructed, upon which circuit simulations effectively confirm the numerical plots.

Deformation dependencies of sand stiffness

Convention does not provide a solution combining drained and undrained response, loss and recovery of sand stiffness, all in one irregular loading sequence. Alas, such solution is necessary for designing offshore wind turbine foundations and predicting soil behavior during (and after) seismic events. To gain deeper understanding of the fundamental phenomenon governing disturbed sand behavior, unconventional testing procedures were attempted using a frictionless triaxial apparatus. The resulting observations revealed a new physical phenomenon (deformation dependent stiffness hysteresis loops). The new observations were then used to derive an unconventional model (BSM), which uses a strain (deformation) envelope.

Enhanced Electrocaloric Effect and Energy Storage Density of Nd‐Substituted 0.92NBT‐0.08BT Lead Free Ceramic

Eco‐friendly 0.92(Na0.5Bi0.49Nd0.01TiO3)‐0.08(BaTiO3) [denoted as NBNT‐BT 92/8] ceramic is synthesized with the help of conventional solid state reaction route. The structural phase pure studies reveals, the compound stabilizes into mixed phase of Cc + P4 mm and the surface morphology of microstructure shows the uniform distribution of Nd. The temperature dependent dielectric study reveals two typical anomalies with the diffuse phase transition and show the relaxor future estimated with the help of diffusivity (γ). From the temperature dependent polarization and room temperature bipolar strain hysteresis loops over broad electrical field range from (0–73) kV cm−1, the estimated energy storage density, energy storage efficiency, and strain values are Wrec ≈ 1.53J cm−3, η ≈ 93(%), and S(%) ≈ 0.4, respectively, which is the best obtained value among available various reported lead‐free piezoelectric ceramics. The adiabatic or electrocaloric temperature change (ΔT) is calculated to be ΔT ≈ 0.95 K at 50 kV cm−1. The obtained valued of ΔT, strain and energy storage density for NBNT‐BT 92/8 is tremendous enhancement compared with absence of Nd in NBT‐BT 92/8.

Amorphous InGaZnO4 Neuron Transistors with Temporal and Spatial Summation Function**Supported by the National Science Foundation for Distinguished Young Scholars of China under Grant No 61425020, the Zhejiang Provincial Natural Science Foundation of China under Grant No LR13F040001, and the National Natural Science Foundation of China under Grant No 51502131.

Amorphous InGaZnO4 neuron transistors based on multi-gate electric-double-layer modulation are fabricated by photolithography processes. The sweeping rate dependent output current and hysteresis loop are observed due to the proton dynamic process in the SiO2 nanogranular electrolyte. Temporal summation such as paired-pulse facilitation is mimicked in the neuron transistor with one presynaptic input. At the same time, supralinear spatial summation of two presynaptic inputs is also successfully mimicked in the neuron transistor with two presynaptic inputs. Our InGaZnO4 neuron transistors with temporal and spatial summation function are interesting for the brain-inspired neuromorphic system.

Size and density controlled Ag nanocluster embedded MOS structure for memory applications

Metal-nanoclusters (NC), deposited by magnetron-based nanocluster source coupled with quadrupole mass filter (QMF) assembly having independent control over their size and density, are used in fabricating NC-based non-volatile memory (NVM) devices. The effect of diameter and density on the NVM charge storage characteristics are presented where Ag is used as the metal NC. The Ag-NC, sandwiched between HfO2 tunnel and control oxides, is deposited by using the combination of the above two instruments. No annealing is performed at any stage of the device fabrication. The largest hysteresis loop area in the capacitance-voltage (C−V) characteristics of metal-oxide-semiconductor (MOS) characteristics is observed for a cluster density of 1×1011cm−2. Further, an NC size dependent hysteresis loop area is observed with the MOS devices where the NC diameter is varied from 3 to 1.5nm keeping the NC density at 1×1011cm−2. The device performance is found to be improved with a reduction of the NC size and shows its best with the NC diameter of 1.5nm. The storage time of the NVM devices also increases with the decrease in the NC diameter and exhibits their best performances for the NCs with a diameter of 1.5nm.

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Segmented magnetic nanowires are a promising route for the development of three dimensional data storage techniques. Such devices require a control of the coercive field and the coupling mechanisms between individual magnetic elements. In our study, we investigate electrodeposited nanomagnets within host templates using vibrating sample magnetometry and observe a strong dependence between nanowire length and coercive field (25 nm–5 μm) and diameter (25–45 nm). A transition from a magnetization reversal through coherent rotation to domain wall propagation is observed at an aspect ratio of approximately 2. Our results are further reinforced via micromagnetic simulations and angle dependent hysteresis loops. The found behavior is exploited to create nanowires consisting of a fixed and a free segment in a spin-valve like structure. The wires are released from the membrane and electrically contacted, displaying a giant magnetoresistance effect that is attributed to individual switching of the coupled nanomagnets. We develop a simple analytical model to describe the observed switching phenomena and to predict stable and unstable regimes in coupled nanomagnets of certain geometries.

Azimuthal angular dependent hysteresis loops of Fe50Mn50/Ni81Fe19 bilayers grown under a magnetic field

The azimuthal angular dependence of the vectorial hysteresis loops in the Fe50Mn50(AF)/Ni81Fe19(F) bilayer grown under a magnetic field was investigated using a combination of vectorial magneto-optic Kerr effect and model calculation. From a comparison of the experimental and calculation results, it is found that the AF easy axis is not parallel with but rotated by about 20° away from the applied magnetic field during the sample growth. Moreover, the transverse loop at the AF easy axis does not vanish but displays an open full circle (i.e., magnetization changes sign between decreasing and increasing field branches for the full hysteresis measurement). Our model calculation reveals that they are reminiscent of the non-collinear uniaxial and unidirectional anisotropies. Specifically, the angular dependence of the transverse hysteresis is well reproduced with our model calculation taking non-collinear magnetic anisotropies into account. Coercivity determined from the longitudinal loops, on the other hand, is found to be nonzero and comparatively large at all azimuthal angles. This is in stark contrast with previous results regarding FeMn/NiFe bilayers field-cooled after sample growth. Neither domain wall nor incoherent magnetic rotation in the F layer is likely to be responsible for this coercivity discrepancy between theory and experiments. Apart from the uniaxial F and unidirectional AF-F anisotropies, we suggest that the F rotatable anisotropy equivalent of 40% to 60% of the interfacial coupling energy should be taken into account to properly address the coercivity enhancement in the FeMn/NiFe bilayer grown under a magnetic field.