Asymmetry Of Hysteresis Loops Research Articles

Center of mass method for exchange bias measurements

Exchange bias measurement techniques are tested using an Ising model for exchange-coupled bilayer structures. In the presence of hysteresis loop asymmetry, the conventional exchange bias characterization method of measuring the sum of the coercive fields is found to be rather inaccurate if compared to the interface coupling energy. An alternative method based on the analysis of entire hysteresis loops is proposed, tested, and found to be substantially more robust.

Asymmetrically shaped hysteresis loop in exchange-biased FeNi/FeMn film

The magnetization reversal of the bilayer polycrystalline FeNi(50 Å)/FeMn(50 Å) film sputtered in a magnetic field has been studied by magnetic and magneto-optical techniques. The external magnetic fields were applied along the easy or hard magnetization axis of the ferromagnetic permalloy layer. The asymmetry of hysteresis loop has been found. Appreciable asymmetry and the exchange bias were observed only in the field applied along the easy axis. The specific features of magnetization reversal were explained within the phenomenological model that involves high-order exchange anisotropy and misalignment of the easy axes of the antiferromagnetic and ferromagnetic layers. It has been shown that the film can exist in one of three equilibrium magnetic states in the field applied along the easy axis. The transitions between these states occur as first-order phase transitions. The observed hysteresis loop asymmetry is related to the existence of the metastable state.

Time dependence of hysteresis loop displacement in hard–soft magnetic systems

Time dependence of the hysteresis loop asymmetry observed in partially crystallized Co 66 Si 16 B 12 Fe 4 Mo 2 is here analyzed at room temperature. The results are related to a magnetic aftereffect occurring in the hard crystallites embedded in the residual soft matrix. The coercive field is found to be constant with time, which is explained in terms of the dipolar interaction theory.

Ferroelectric Thin Film Properties: Peculiarities Related to Mismatch-Induced Polarization

The ferroelectric thin film properties were calculated in phenomenological theory framework. Surface energy that defined boundary conditions for Euler-Lagrange differential equation was written as surface tension energy. The latter was expressed via surface polarization and tension tensor related to mismatch of a substrate and a film lattice constants and thermal expansion coefficients. The calculations of the film polarization distribution, temperature, thickness and external electric field dependence and hysteresis loops as well as average dielectric susceptibility dependence on temperature and film thickness have been performed allowing for mismatch-induced polarization Pm. The obtained asymmetry of hysteresis loop makes it possible to suppose that the self-polarization phenomenon recently observed in some films is related to mismatch effect. The large enough mismatch effect (|Pm|/PS > 1) could be the physical reason of ferroelectric phase conservation in ultrathin film. The possibility to observe the peculiarities of the films properties temperature and thickness dependencies related to mismatch effect is discussed.

Imprint and oxygen deficiency in (Pb,La)(Zr,Ti)O3 thin-film capacitors with La-Sr-Co-O electrodes

La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O thin-film capacitors have been grown in various oxygen ambients by pulsed laser deposition. As the oxygen ambient became more reducing, the capacitors developed more voltage asymmetry in hysteresis loops and a more preferred polarization state directed towards the top electrode. PLZT capacitors cooled in a fully oxidizing atmosphere (i.e., 1 atm oxygen pressure) exhibited nominally symmetric hysteresis loops and also showed little imprint both with and without fully saturating bias fields. We find that ambient oxygen pressure is an important process parameter and the imprint behavior is closely related with ambient oxygen induced effects such as oxygen vacancies, its related defect-dipole complexes and trapping of free charges. The different imprint behavior under negative and positive bias also suggests that the dipolar-defect complexes tend to cause imprint in PLZT capacitors.

Growth and electrical properties of Pb(Zr,Ti)O3 thin films by sputtering using an alloy target

Abstract Pb(Zrx,Ti1−x)O3 thin films were deposited on Pt/SiO2/Si substrates by the rf magnetron sputtering using an alloy target consisting of Zr-Ti alloy and Pb metal. The dependence of electrical properties on film thickness and sputtering gas pressure was investigated. The dielectric constant and the remanent polarization decreased and the coercive field increased with the decrease of the film thickness. In the dependence of gas pressure, the relative dielectric constant of the film with only a perovskite phase were in the range of 235–280, which were higher than those of the film with only a pyrochlore phase, 20. The asymmetry of hysteresis loops increased with the decrease of the gas pressure.

Depolarization and hysteresis loop asymmetry in PZT thin films with self polarization

Abstract In the present paper, we have investigated ferroelectric polarization switching, self polarization, (Pself), rapid depolarization, which we call AP, and the asymmetry of hysteresis loops in thin lead-zirconate-titanate (PZT) films prepared by a solution technique. For comparison we have used bulk PZT ceramics, whose ferroelectric switching behavior is well understood, to demonstrate the measurement principal.

Imprint of La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O Heterostructures Grown by Pulsed Laser Deposition

ABSTRACTLa-Sr-Co-O(LSCO)/Pb-La-Zr-Ti-O(PLZT)/La-Sr-Co-O heterostructures with different crystalline quality have been grown on LaAlO3 and Si with a bismuth titanate template layer. Imprint of the heterostructures are investigated in comparison with fatigue and retention. Oxygen ambient during cooling the heterostructures was also varied to investigate the imprint. With consideration of the switching behavior caused by imprint, imprint behavior was deconvoluted from fatigue and retention. In epitaxial PLZT capacitors grown on LaAlO3, imprint behavior was found to be significantly dependent on the oxygen ambient. As the oxygen ambient became more reducing, the capacitors developed more voltage asymmetry in hysteresis loops and a more preferred polarization state directed towards the top electrode. On the other hand, oriented PLZT capacitors exhibited less pronounced effect of the oxygen ambient on the imprint behavior.

A Model of The Metal-Ferroelectric-Metal Capacitor

AbstractFerroelectric (FE) films, especially PZT films, have received increasing attention for microelectronic applications such as ferroelectric memory and high density DRAM. There has been significant progress in the preparation of high quality PZT films involving wet chemical and physical vapor deposition techniques. Metal-FE-metal structures, typified by Pt-PZT-Pt capacitors, are the basic building blocks for the ferroelectric devices. The leakage currents of the capacitors are known to be non-ohmic and exhibit an exponential dependence on applied voltage.The present paper presents a model based on totally depleted back-to-back Shottky barriers. Predictions based on the model can provide significant new understanding of the FE behavior of thin films. For example, the assumption of total depletion leads to the presence of a built-in field within the film which can explain the ubiquitously higher values of coercive field in FE films than found in bulk ceramics. It will be shown that the agreement between model predictions and actual device I-V characteristics of Pt-PZT-Pt capacitors is very close. Further, the model can also explain the observed hysteresis loop asymmetry and low dielectric constants of films of relaxor FE's, whose dielectric constants are much smaller than those of bulk materials.

A re-evaluation of fatigue threshold test procedures and the simulation and prediction of fatigue crack growth under conditions of low crack closure. (Dissertation): Herman, W.A. Diss. Abstr. Int.50, (2), 188 pp, Aug. 1989

Anisotropic fatigue and cyclic behaviour of AM30 Mg alloy extrusion is investigated by performing fully-reversed strain-controlled tension-compression cyclic tests at strain amplitudes between 0.3% and 2.3%, along extrusion (ED) and transverse (TD) directions. The shapes of half-life hysteresis loops suggest the predominance of slip and twinning/de-twinning mechanisms below and above the strain amplitude of 0.5%, respectively. The twinning/de-twinning occurrence is found to be more extensive during straining along ED, which results in higher asymmetry of hysteresis loops, and thereby, higher induced mean stress. This adversely affects the fatigue resistance and yields to less number of cycles before failure in ED. Optical microscopy and texture analysis are employed to validate the findings. In addition, fracture surfaces are studied by scanning electron microscopy to identify the sources of fatigue crack initiation. Persistent slip bands (PSBs) and twin lamellae interfaces are evidenced as crack initiation sites at low and high strain amplitudes, respectively. Cracks emanated from debonded inclusion interface are also observed. Lastly, estimated fatigue life by Smith-Watson-Topper (SWT) and Jahed-Varvani (JV) fatigue models are compared with experimental life obtained through this study as well as the ones reported in the literature. The JV energy model is proven to yield better life predictions.

A data acquisition and control program for axial-torsional fatigue testing. (Report): Kalluri, S. and Bonacuse, P.J. NASA Lewis Research Center Report No TM-102041 1989, 21 pp

Anisotropic fatigue and cyclic behaviour of AM30 Mg alloy extrusion is investigated by performing fully-reversed strain-controlled tension-compression cyclic tests at strain amplitudes between 0.3% and 2.3%, along extrusion (ED) and transverse (TD) directions. The shapes of half-life hysteresis loops suggest the predominance of slip and twinning/de-twinning mechanisms below and above the strain amplitude of 0.5%, respectively. The twinning/de-twinning occurrence is found to be more extensive during straining along ED, which results in higher asymmetry of hysteresis loops, and thereby, higher induced mean stress. This adversely affects the fatigue resistance and yields to less number of cycles before failure in ED. Optical microscopy and texture analysis are employed to validate the findings. In addition, fracture surfaces are studied by scanning electron microscopy to identify the sources of fatigue crack initiation. Persistent slip bands (PSBs) and twin lamellae interfaces are evidenced as crack initiation sites at low and high strain amplitudes, respectively. Cracks emanated from debonded inclusion interface are also observed. Lastly, estimated fatigue life by Smith-Watson-Topper (SWT) and Jahed-Varvani (JV) fatigue models are compared with experimental life obtained through this study as well as the ones reported in the literature. The JV energy model is proven to yield better life predictions.

Hysteresis loop asymmetry induced by magnetic annealing in Fe-Al alloy

It is experimentally shown, by means of convenient magnetic annealing treatments, that the hysteresis loop of an Fe-Al alloy can be modified in a strongly asymmetric way. A zero differential permeability can be obtained along magnetic field intervals at any given point of the loop. This phenomenon, besides producing ferromagnetic materials having very peculiar characteristics, provides fundamental information about the effects of mutual interactions among Bloch walls during their movement towards a given configuration, stabilized by annealing. Moreover, the experimental results show that stabilization of a given wall configuration, performed under pressure exerted by an external magnetic field, has unidirectional features, limiting more effectively wall movements in the same direction as the pressure applied during the heat treatment. This proves that potential energy wells of asymmetric shape can be created within the alloy by means of convenient annealing techniques.