Papers by Keyword: Magnetic Hysteresis

Abstract: A model of the rearrangement of the domain structure of the Tb_0.2Y_2.8Fe₅O₁₂ garnet ferrite in the temperature region of the spontaneous reorientation of the easy magnetization axis is proposed, which makes it possible to consistently describe (at a qualitative level) the entire set of experimental results obtained. The latter makes it possible to make a choice in favor of the fluctuation mechanism of nucleation of domains of a new magnetic phase in the process of reorientation of the direction of the easy magnetization axis.

Abstract: The results of studies of magnetic and thermoelectric properties of pearlite, martensitic and austenitic steels, as well as cobalt and nickel based alloys are presented. The magnetization curves for materials from among the studied ones, as well as dependences of absolute thermoelectric power on the material temperature, are obtained. It was found that for ferromagnetic substances in weak magnetic fields the dependence of magnetic induction on the magnetic field strength is non-linear. This allows to conclude that magnetic permeability of such medium is not a constant, but can be described, for example, by a third-order polynomial.

Abstract: Magnetism of reduced graphene oxide/rGO prepared by a green synthesis method from coconut shells (rGO-s) and the commercial product (rGO-c, ®Graphenea) have been investigated. Similar magnetic feature of a weak ferromagnetism concomitant with diamagnetic nature was observed in both samples. At 300 K, the saturation magnetization (M_S) of rGO-s is approximately 14×10^-3 emu/g, which is about 3 times of that observed in rGO-c (~5×10^-3 emu/g). The noticeable difference in the M_S is suggested due to the different concentration of oxygen-functional groups and other defects presented in the rGO sheets. The samples have similar structure and contains similar functional groups, yet rGO-s contains higher concentration of oxygen-functional groups and defects than rGO-c. A paramagnetic behavior was also indicated at low temperature. This study supports an indication of the defect-induced-magnetism in rGO and confirms that various magnetic features, such as ferromagnetic, diamagnetic and paramagnetic, can coexist in rGO.

Abstract: Magnetic hysteresis properties of nanostructured industrially manufactured Nd-Fe-B and Pr-Fe-B alloys on the base of a tetragonal Nd₂Fe₁₄B (2-14-1) hard magnetic phase (MQP-B, MQP-B+ and MQP-16-7 brands) have been investigated at 4.2 K in magnetic fields up to 58 T. The chemical composition of the alloys given in the certificates was defined more precisely. The grain sizes of the main 2-14-1 phase were determined. The average grain size is much smaller than a critical single domain diameter. Coercivity, remanence magnetization, saturation magnetization and maximal magnetic energy product were determined at 4.2 K and compared with those obtained at room temperature.

Abstract: One of the main characteristics of Terfenol-d is the magnetic hysteresis, which leads to nonlinearity in mechanical-magnetic behavior. In this paper, magnetic hysteresis of Terfenol-d at different frequencies has been studied experimentally and theoretically. For experimental study, a setup has been fabricated and major hysteresis and first order reversal loops were obtained at different frequencies. Mathematical modeling of magnetic hysteresis has been done by introducing a new hybrid model which is developed by combination of Preisach and Tangent Hyperbolic models. The hybrid model can reduce the number of experiments and can be used for both frequency-independent and frequency-dependent hysteresis states.

Abstract: In this paper the magnetostrictive material considered is Terfenol-D. Its hysteresis is modeled by applying the DPM whose identification procedure is performed by using a neural network procedure previously publised [. The neural network used is a multiplayer perceptron trained with the Levenberg-Marquadt training algorithm. This allows to obtain the Preisach distribution function, without any special conditioning of the measured data, owing to the filtering capabilities of the neural network interpolators. The model is able to reconstruct both the magnetization relation and the Field-strain relation. The model is validated through comparison and prediction of data collected from a typical Terfenol-D transducer.

Abstract: Magnetic hysteresis effects, present in the force of an E-core reluctance actuator, are examined by simulations and measurements. Simulations have been performed with a 3d finite element method (3d-FEM) and a Preisach model, which is extended with a dynamic magnetic equivalent circuit (MEC) model. Both simulation methods are first examined on the prediction of the magnetic flux density in a closed-and open toroid for dc-and ac excitations. Finally, both methods are used to predict the force of the E-core reluctance actuator, which is compared to ac force measurementsperformed with a piezoelectric load cell.

Abstract: This work used Artificial Neural Network (ANN) to investigate the hysteresis behavior of the Ising spins in structures ranging from one-to two-and three-dimensions. The equation of magnetization motion under the mean-field picture was solved using the Runge-Kutta method to extract the Ising hysteresis loops with varying the temperature, the external magnetic field parameters and the system structure (via the variation of number of nearest neighboring spins). The ANN was then used to establish relationship among parameters via Back Propagation technique in ANN training. With the trained networks, the ANN was used to predict hysteresis data, with an emphasis on the dynamic critical point, and compared with the actual target data. The predicted and the target data were found to agree well which indicates that the ANN functions well in modeling hysteresis behavior and its critical phase diagram across systems with different structures.

Abstract: We investigated the magnetization switching process in a bilayered exchange spring system through micromagnetic simulations. A typical exchange coupled magnetic hysteresis loop was observed in this work. The influence of magnetocrystalline anisotropy constant on the magnetization of the exchange spring structure was also studied. It is demonstrated that the film thickness of hard layer play a more important role than that of soft layer to the influence on coercive field and shape of the hysteresis loop.

Abstract: Magnetoelectric effect in multiferroic materials is widely studied for its fundamental interest and practical applications. The magnetoelectric effect observed for single phase materials like Cr₂O₃, BiFeO₃, Pb(Fe_0.5Nb_0.5)O₃ is usually small. A much larger effect can be obtained in composites consisting of magnetostrictive and piezoelectric phases. This paper investigates the magnetostrictive and magnetoelectric properties of nickel ferrite Ni_0.3Zn_0.62Cu_0.08Fe₂O₄ - relaxor Pb(Fe_0.5Nb_0.5)O₃ bulk composites. The magnetic properties of composites shows a dependence typical of such composite materials, i.e. it consists of a dominating signal from ferrimagnetic phase (ferrite) and a weak signal from paramagnetic (antiferromagnetic) phase (relaxors). Magnetoelectric effect at room temperature was investigated as a function of static magnetic field (300-7200 Oe) and frequency (10 Hz-10 kHz) of sinusoidal modulation magnetic field. The magnetoelectric effect increase slightly before reaching a maximum at H_DC = 750 Oe and then decrease. The magnetoelectric coefficient increases continuously as frequency is raised, although this increase is less pronounced in the 1-10 kHz range.