Minor Loop Behavior Research Articles

Giant exchange bias induced by spin-glass and antiferromagnetic coupling in Fe2−xGaxTeO6 single crystals

It is known that the utilization of exchange bias (EB) effect for data storage underscores its importance. However, achieving a giant EB effect with a small cooling field (HCF) in single-phase materials remains a challenge. This study unveils a giant EB value within a single-phase material, Fe2−xGaxTeO6 (FGTO), originating from the anchoring of spin-glass phase by antiferromagnetic order. Manipulating the relative strengths of the spin-glass and antiferromagnetic order parameters by Ga3+-substitution of Fe3+ ions in the Fe2TeO6 lattice governs the magnitude of the EB effect. It is found that FGTO single crystals synthesized via the chemical vapor transport do exhibit a remarkably large EB value as large as 1.5 T at x = 0.50 and a quite small cooling field HCF = 50 Oe. Investigations on the training effect, minor loop, and relaxation behavior unravel the intricate dynamics inherent to the spin-glass state. This study not only establishes a platform for exploring the EB effect in single-phase materials but also illuminates potential applications of FGTO in the realm of spintronics.

Magnetic hysteresis model using chained plays

A magnetic vector hysteresis model is presented using play hysterons as building blocks. The main difference compared to earlier play based magnetic hysteresis models is that instead of forming a superposition of plays with different coercivities, this work uses a set of identical plays which are connected in a chain so that the output of one play acts as input to the next. Like models using a superposition, this yields far more complex minor loop behavior than a single play is capable of. Comparisons are made with measurements on a nonoriented electric steel for BH curves and alternating and rotational losses, showing satisfactory agreement. The approach is found to have both advantages and disadvantages compared to models using superpositions of plays. The problem of determining model parameters becomes simpler and the model can be reversed so either magnetic field or magnetization may be used as known variable. On the other hand, there is no apparent connection to underlying physical processes.

An Alternative Way for Reconfigurable Logic-in-Memory With Ferroelectric FET

Single ferroelectric-FET (FeFET) reconfigurable logic-in-memory is an attractive beyond-von-Neumann scheme for data-centric computing. Different from using body-to-source voltage to tune the operating point of the FeFET for reconfigurability, this brief presents an alternative approach based on the unique ferroelectric minor-loop behavior (which results from the partial switching of domains). Through simulation, we show that the NAND/ NOR reconfigurability can theoretically be achieved by adequately modulating the reference and writing pulses for the FeFET nonvolatile memory (NVM). Our approach may serve as an option when the body-effect capability is lacking for nonplanar FeFETs or 3-D stacked FeFETs which can be crucial to future high-density integration.

Viscous magnetization decrease in first-order reversal curves induced by rotatable magnetic anisotropy in polycrystalline exchange-biased bilayers

A prototypical polycrystalline in-plane exchange bias system exhibited a viscous decrease of the ferromagnetic magnetization upon increasing external magnetic field when measuring first-order reversal curves. The phenomenon is investigated by means of angular-resolved vectorial magneto-optical Kerr magnetometry complemented by fits of model calculations and by Kerr microscopy. It is found that the viscous magnetization decrease is mediated by a rotatable magnetic anisotropy arising from thermally unstable antiferromagnetic grains coupled to the probed ferromagnet. This additionally manifests itself by a creeping domain wall motion in the ferromagnet due to thermally activated processes in the antiferromagnet. The investigations are in agreement with a generalized description of polycrystalline exchange bias systems and emphasize the relevance of understanding minor loop behavior addressing nonsaturated magnetic states for systems susceptible to dynamic changes on the hysteresis loop timescale.

An Analysis of Minor Hysteresis Loops Behavior under PWM Voltage - Electromagnetic Device at No-Load and Loaded Conditions

This paper addresses the influence of the primary and secondary resistances on the behavior of minor hysteresis loops when the electromagnetic device is fed by three-level PWM (pulse width modulation) voltage. To study the device transferring energy to a load, the experimental approaches are different of traditional procedures to material characterization, where problems inherent to the process are added. Analytical, FEM and experimental analysis are performed on a toroidal transformer equipped with a flux sensing coil. The leakage fluxes related to the primary and secondary currents are shown to cause errors in the measurement of the core magnetization current. A solution to mitigate this problem is employed, consisting in twisting and winding together primary and secondary conductors. Experimental methodologies for obtaining the value of the iron losses when the device is transferring energy to a load are also performed. The study shown showed that supply voltage with three-level PWM waveform causes minor hysteresis loops and the greater the resistance value of the excitation winding, the larger the areas of the minor hysteresis loops. On the other hand, by increasing the energy transferring to a load the minor loops areas tend to decrease.

Minor hysteresis patterns with a rounded/sharpened reversing behavior in ferromagnetic multilayer

Hysteresis of ferromagnetic system exhibits a fundamental stimulus-response behavior, thereby casting all the important macromagnetic system parameters such as coercivity, nucleation field, saturation magnetization, and hysteresis loss. Recently, increasing attention has been paid to exploration of relatively less understood minor loop behavior, since faster operation of magnetic devices is inevitably accompanied by minor hysteresis behavior from cycling among unsaturated ferromagnetic states. Here, we report our microscopic investigation of unusual minor hysteresis loop behavior, represented by rounded or sharpened response of minor hysteresis loop of (CoFeB/Pd)4 multilayer film. It is observed that rounded and sharpened response in the minor hysteresis response could be manifested under proper conditions. The minor loop behavior has been systematically investigated by direct microscopic magnetic domain observation using magneto-optical Kerr microscopy. The rounded response of magnetization at the reversing external field along the minor hysteresis curve, so far neglected or considered as one of ‘unusual’ behaviors, has been found to be elaborately controllable by tuning the reversing field strength and the field sweep rate for multilayers with low repeat numbers. Variable roundedness of the minor hysteresis loop is understandable based on the analysis of magnetic domain dynamics such as domain nucleation and the domain wall velocity.

Solution combustion synthesis method and magnetic properties of synthesized polycrystalline calcium manganite CaMnO3−δ powder

We present a modified solution combustion synthesis method and measured magnetic properties of CaMnO3-δ (calcium manganite). The structure, morphology and magnetic properties of CaMnO3-δ were investigated by XRPD (X-ray powder diffraction), TEM (transmission electron microscopy), HRTEM (high-resolution transmission electron microscopy) and SQUID (superconducting quantum interference device). The XRPD study revealed that the prepared sample is composed of pure calcium manganite phase. The TEM and HRTEM images showed well-crystallized particles with a rough surface and particle size of about 100nm. Magnetization measurements revealed magnetic transition at TN=120K, which corresponds to the Neel temperature of calcium manganite. Paramagnetic behavior was measured above the TN temperature. High irreversibility between the ZFC (zero-field cooled) and the FC (field cooled) curves below TN were observed. In addition, the separation between ZFC and FC curves increased with increasing magnetic field. We also show that the temperature values at the maxima of the ZFC curves are insensitive to the value of the applied DC magnetic field and to the frequency of the AC magnetic field. Magnetic measurements also indicate the presence of a strong antiferromagnetic exchange coupling with a Curie-Weiss temperature θ=−436K. Magnetic moment of 4.33 μB per Mn ion is determined from the Curie constant. This value of the magnetic moment suggests that Mn3+ and Mn4+ ions exist in the sample. Measurements of the magnetic hysteresis properties indicate a contribution of a ferromagnetic-like component in the sample. This is revealed by large coercivity and high remanence magnetization below TN. In this work we also studied field-cooled (up to 5T) hysteresis properties of the sample. The detailed analysis of these results suggests a minor hysteresis loop behavior and no exchange bias.

Specific features of magnetic properties of ferrihydrite nanoparticles of bacterial origin: A shift of the hysteresis loop

The results of the experimental investigation into the magnetic hysteresis of systems of superparamagnetic ferrihydrite nanoparticles of bacterial origin have been presented. The hysteresis properties of these objects are determined by the presence of an uncompensated magnetic moment in antiferromagnetic nanoparticles. It has been revealed that, under the conditions of cooling in an external magnetic field, there is a shift of the hysteresis loop with respect to the origin of the coordinates. These features are associated with the exchange coupling of the uncompensated magnetic moment and the antiferromagnetic “core” of the particles, as well as with processes similar to those responsible for the behavior of minor hysteresis loops due to strong local anisotropy fields of the ferrihydrite nanoparticles.

The Minor Hysteresis Loop Under Rotating Magnetic Fields in Machine Laminations

In rotating ac machines, the saturated flux density waveforms contain harmonics, which create minor hysteresis loops. The minor hysteresis loops in machine laminations constitute an additional loss which requires modifications in traditional core loss formulas. This causes a serious challenge in core loss estimation. The task becomes more competitive under rotating magnetic fields, where the minor loop behavior has not been investigated yet. This paper highlights the problem of harmonics in rotating fields and its effect on the core loss estimation. In addition, the behavior of minor loops under rotating fields is compared with the minor loops under pulsating fields. Measurements were carried out on a nonoriented silicon steel sample of M36G29 with different fundamental frequencies of interest to the industry, 60 Hz and 400 Hz, with consideration of the third harmonic at each frequency. A design of magnetizing test fixture based on an electromagnetic Halbach array is used to perform these measurements. Results are presented and discussed.

Effect of Carrier Frequency and Circuit Resistance on Iron Loss of Electrical Steel Sheet Under Single-Phase Full-Bridge PWM Inverter Excitation

The pulse width modulation (PWM) inverter has been used for the control of a motor since the rotating speed can be changed efficiently and easily. In order to estimate the iron loss in an iron core with sufficient accuracy under a PWM inverter excitation, it is necessary to understand correctly the influence of operating condition and circuit parameter on iron losses. In this paper, we measured magnetic properties of the nonoriented electrical steel sheet excited by a single-phase full-bridge PWM inverter using a ring specimen that corresponds to a magnetic circuit of an actual motor core. The effect of the carrier frequency and circuit resistance on the iron loss and the behavior of minor loops was examined. It is shown that the iron loss is increased when the circuit resistance is increased due to the generation of minor loops. Therefore, the circuit resistance should be decreased in an actual motor system.

Nonlinear magnetoelectric behavior of Terfenol-D/PZT-5A laminate composites

In this paper, a comprehensive experimental study and modeling of the nonlinearbehavior of Terfenol-D/PZT-5A magnetoelectric laminate composites is reported.Magnetostriction versus magnetic field of an individual Terfenol-D sample of dimensionslength = 22 mm,width = 19 mm,thickness = 0.683 mm, and polarization versus electric field as well as strain versuselectric field of an individual PZT-5A sample of dimensionslength = 22 mm,width = 19 mm,thickness = 0.127 mm were characterized. These samples were bonded to form a symmetricPZT-5A/Terfenol-D/PZT-5A laminate composite to avoid bending–extensioncoupling. Electric response of this composite to magnetic input was comprehensivelycharacterized to include major loop and minor loop behavior. A modeling approach thatstructurally couples the nonlinear magnetostrictive Terfenol-D behavior and linearPZT-5A behavior to predict the magnetoelectric response was developed andvalidated against experimental results. This analysis, with further refinements,could prove to be a useful tool to model and design magnetoelectric sensors.

Cumulative minor loop growth in Co/Pt and Co/Pd multilayers

The behavior of minor hysteresis loops in perpendicular anisotropy [Co/Pt] and [Co/Pd] multilayers has been investigated. Upon applying a succession of identical magnetic field cycles, we observe a very substantial cumulative growth of the minor loop area. For the [Co/Pt] multilayers this effect only saturates near complete magnetization reversal while the behavior is slightly more limited for [Co/Pd] multilayers. We also find this cumulative growth to occur even if the minor loop field cycles are made asymmetric by means of a positive bias field. The cumulative behavior persists up to a sample-dependent threshold value above which this effect disappears. In all samples, the cumulative minor loop growth is correlated with a small reduction in the maximum magnetization value in each cycle. Magneto-optical Kerr microscopy studies correlate the minor loop growth with the memory and cumulative expansion of lateral domain cycling. All experimental observations can be consistently explained as an accumulation of small nucleation domains that aid subsequent reversals and facilitate the cumulative minor loop growth.

Magnetic properties of α′ martensite in austenitic stainless steel studied by a minor-loop scaling law

We study the scaling behavior of magnetic minor hysteresis loops in strain-induced ferromagnetic α′ martensites in an austenitic 316-type stainless steel. A scaling relationship between the hysteresis loss and the remanence, with a power law exponent of approximately 1.35, was found irrespective of the volume fraction of the α′ martensites as well as temperature. The coefficient of the power law largely decreases with volume fraction, whereas it increases with a decrease in temperature and exhibits a kink at around 40 K, close to the Néel temperature of an austenitic γ′ phase. The behavior of the coefficient was interpreted from the viewpoint of the morphology and exchange interaction of α′ martensites.

Characteristics of GaMnAs‐based double‐barrier TMR structures

We have investigated the tunneling magnetoresistance (TMR) in GaMnAs-based double barrier magnetic tunneling junctions (DB-MTJs) to clarify the origin of extremely low threshold current density for current-driven magnetic orientation reversal achieved in the systems. The TMR characteristics including minor loop behavior are well explained by assuming that three magnetic layers in the DB-MTJ have different coercive forces and that the uniaxial magnetic anisotropy in the middle magnetic layer is enhanced with decreasing the layer thickness. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spin-Dependent Scattering in Multilayered Magnetic Rings

Narrow mesoscopic NiFe/Cu/Co elliptical rings exhibit room-temperature giant magnetoresistance with distinct resistance levels corresponding to three different micromagnetic states. The highest and lowest resistance states of the multilayer rings correspond to the Co layer being in a bidomain state, antiparallel or parallel, respectively, to the NiFe, while the intermediate resistance corresponds to the Co layer being in a vortex state. Micromagnetic simulations suggest that the behavior of these rings is dominated by magnetostatic interactions between the domain walls in the Co and NiFe layers. Additional magnetization states in the NiFe at low applied fields can account for the minor loop behavior.

A Free Energy Model for the Inner Loop Behavior of Pseudoelastic Shape Memory Alloys

AbstractThe paper presents a free energy model for the pseudoelastic behavior of shape memory alloys. It is based on a stochastic homogenization process, which uses distributions in energy barriers and internal stresses to represent effects typically encountered in polycrystalline materials. This concept leads to a realistic desription of the rate-dependent inner loop behavior, but is characterized by rather long computation times. This is prohibitive in regard to a potential implementation into other numerical codes, such as finite element or optimal control programs or a Matlab/Simulink environment. For this purpose a parameterization method is introduced, which is derived from the concept of a representative single crystal. The approach preserves the desirable properties of the original formulation, at the same time reducing the numerical effort significantly. Finally, we show that the method can reproduce the experimentally observed behavior accurately over a large range of strain rates including the minor loop behavior.

スパッタ法により作製したＣｏ‐Ｐｔ薄膜の磁気特性およびＭＦＭ探針への応用

CoxPt100-x (33 ≤ x ≤ 97) thin films were fabricated by RF sputtering method with various sputtering Ar gas pressure PAr and film thickness t and applied to hard magnetic tips for Magnetic Force Microscopy (MFM). The coercivity Hc of Co-Pt films, which were fabricated under high PAr, increased in the Co concentration range beyond 60at. % Co. The maximum value of μ0Hc, 0.27T was obtained for the Co79Pt21 films with PAr=10.7Pa and t=40nm. X-ray diffraction analysis revealed that hcp phase exists in the films with high coercivity. The anisotropy field μ0Ha of the hcp phase was estimated about 1.0T by singular point detection technique. The high coercivity of the films is attributed to domain wall pinning from the minor loop behavior. The MFM tips with Co79Pt21 films on Si cantilevers gave finer contrast in MFM images than commercial CoCr MFM tips for magnetic recording media.

Minor loop behavior in classical Preisach hysteretic systems

Minor loop behavior have been investigated experimentally on magnetically uniaxial films of YIG based garnets and MnBi all having the easy direction of the magnetization perpendicular to the film plane and unit squareness. In these films the magnetization changes by domain wall motion. A regular two-dimensional array of small, strongly uniaxial particles, etched from one of the films, is switching by rotation. The wiping out property is observed for each sample, however, the congruence of the minor loops is fulfilled only for the 2D array, for minor loops centered on the H=0 axis. Accommodation of minor loops is observed for MnBi. Depending on the start field of the switching process, the samples can be prepared to display minor loops of very different shape.

Effect of uniaxial stress on the reversible and irreversible permeabilities of 2% Mn pipeline steel

The results of a study of the effects of constant uniaxial stress on the irreversible and reversible differential permeabilities of minor and saturation major hystersis loops are presented, extending an earlier study which studied those permeability components on the initial magnetization curve. Tension was found to increase both the reversible and irreversible components of the saturation major loop differential permeability in the low magnetization region, and to decrease them in the high magnetization region. The opposite effect was found for compression. This effect was explained as the result of changes in the domain structure of the sample when stressed and a resulting change in the ratio of 90/spl deg/ of 180/spl deg/ domain walls. The differences between the upper and lower branches of the saturation major hysteresis loop reversible relative differential permeability were found to increase in tension and decrease in compression, with more complicated behavior occurring in the irreversible component. Minor loop behavior was also found to vary depending on the magnetization of the sample. In the low magnetization region tension was found to produce higher values and larger variations in both components of the relative differential permeability than the unstressed case, while compression produced lower values and smaller variations. The opposite behavior was found to be true in the high magnetization region, while an intermediate behavior with little or no change in both the relative differential permeability components was found to exist between the two extreme cases. The minor loops were measured from set values of the applied field, and tension was found to increase the corresponding values of magnetization, with compression causing a decrease in the magnetization values. The behavior of the minor loops was found to be related to the major loop behavior in the same region. >

Statistical model for ferromagnetic hysteresis (abstract)

An application of the Landau theory of phase transitions to the construction of a thermodynamical equation of state for a uniaxial ferromagnetic crystal is presented. This equation of state is taken as starting point for the construction of a phenomenological constitutive law for bulk ferromagnetic hysteresis. This law describes both alternating and rotational hysteresis, reversible and irreversible magnetization, complex minor and major loop behavior, anhysteretic magnetization, and the Rayleigh relationship for weak fields. A geometrical interpretation, which was discussed briefly earlier (see Ref. 1), is given and it is shown that this law can be understood as an extension of the oft-cited Preisach model to the vectorial case. It is also shown that this law compares favorably with other recent extensions (see Ref. 2). Last, the mathematical problems raised by the solution of the Maxwell field equations in the presence of such constitutive laws are discussed.<ks>