Study of magnetic after-effect in magnesium manganese ferrites

The magnetic after-effect caused by the diffusion of electrons was studied in detail in MnMg ferrites of the series Mg _x Mn_1.15–x Fe_1.85O₄₊ ; the comparative measurements were also carried out on a sample of MgFe₂O₄₊₍<0). By combining the two methods, (a) investigation of the disaccommodation of initial permeability at different temperatures and (b) measurement of the displacement of the maximum of the temperature dependence tan with the frequency, it was possible to study the relaxation processes whose time constants lay between 0.5 sec and several hours, or between 10^–4 to 10^–7 sec. It was found that the processes taking place at low temperatures and studied by method (a) differ from those observed at high temperatures by method (b), particularly in the lower activation energies and greater dispersion of the time constants. In addition to these two main relaxation processes a weak relaxation superposed over the main disaccommodation was found in ferrites with non-zero content of manganese. An analysis of the intensity of different relaxation effects showed the participation of Mn ions in these relaxation effects and it was found that both main relaxations are probably equivalent as regards the final steady state, to the creation of which they lead; they differ however in the mechanism of electron diffusion by which this state is realized. The main features of the different diffusion mechanisms are discussed.

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, , MnMg Mg _x Mn_1.15–x Fe_1.85O₄₊ . MgFe₂O_{4+ (}<0). ()- , () tg , , 0,5 sec , 10^–4–10^–7 sec. , , () , , (), , , . , . Mn , , , , , ; , , , . .

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In conclusion the author thanks Dr. J. Bro and K. Závta for valuable discussion and F. Vilím for carefully carrying out the measurements.     

Origin of the constricted hysteresis loop in cobalt ferrites revisited

A series of Co ferrites (Co_xFe_3−xO₄ (x=0−1)) were prepared using solid-state method in this work. The aging effect of their structures and constrictions of hysteresis loops under low magnetic field were investigated. It was found that during the aging process, the migration of trivalent (bivalent) ions between tetrahedral (A-site) and octahedral (B-site) coordination induced a shrinking of the lattice, which would expand again due to the precipitation of Fe³⁺ after a much longer aging time. The first process caused a pronounced constriction of the loops, due to the uniaxial anisotropy led by this migration. The depression of constriction could attribute to both the expansion of lattice and the change of ionic ratios as a result of the second-phase-precipitation. The impacts of Co content, aging time and temperature upon the constriction were also discussed.     

The dependence of the rectangular hysteresis loop on the external stress in manganese-magnesium and manganese ferrites

The dependence of the shape of the hysteresis loop on the external stress was studied on samples of manganese-magnesium and manganese ferrites. A high value was assumed for the energy of the magnetocrystallic anisotropy of manganese-magnesium ferrites of different composition. The sign of the magnetostriction was determined from the character of the changes inB _r/B_m of the samples.The work was done in 1960 at the Institute of Solid State Physics, Prague.The above results are taken from work on the author's graduate thesis which was done in 1960 in the Institute of Solid State Physics. The author thanks Professor J. Bro, Dr. S. Krupika and other members of the magnetic department of the above institute for valuable remarks.     

磁滞回线和交流电路实验

改进磁滞回线实验,使之能观察包括工频交流电路中的一些基本现象。通过介绍微分回线的概念,使学生了解更我铁实验数据处理方法及其意义。     

Mössbauer-effect study of Mg-Al ferrites having a rectangular hysteresis loop

A Mössbauer-effect study was made of Mg-Al ferrites having a rectangular hysteresis loop. The replacement of Fe³⁺ ions by A1³⁺ ions produces an additional component in the Mössbauer spectra, due to second-phase inclusions. The phase composition of the Mg-Al ferrite has a marked effect on the shape of the hysteresis loop. As the second-phase inclusions increase in relative importance, rectangularity coefficient D decreases. Local lattice distortion has a lesser effect on D. At high Al₂O₃ concentrations (above 15 mole%) in the Mg ferrite there is a sharp increase in the coercive force with increasing Al₂O₃ content. This increase is also due to second-phase inclusions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 105–109, February, 1971.In conclusion the authors thank I. I. Sil'vestrovich and B. A. Pavel'ev for furnishing the samples.     

交换弹簧磁性多层膜的磁矩取向及磁滞回线的解析研究

本文以界面交换耦合常数Jⁱ和软磁相厚度L^s为主要参变量,研究了易轴与膜面平行情况下的Nd₂Fe₁₄B/α-Fe磁性多层膜的磁矩随外场变化的取向及磁滞回线,并得到了成核场的解析公式.分析发现,Jⁱ对磁矩取向、钉扎场和矫顽力机理有着较大的影响.当L^s较小时,钉扎场等于成核场,随着Jⁱ的减小 关键词： 成核场 钉扎场 矫顽力 磁滞回线     

Minor hysteresis loop effects in magnetic materials

In this report we discuss the nature of minor hysteresis in ferromagnets. In particular we have examined the formation of minor loops in which the magnetisation in the second quadrant is at a higher positive value, as the magnitude of H is increasing in a negative sense, than it is during a reverse sweep back to zero field. This behaviour produces the well known elliptical minor loops, or the ‘eye effect’. We have examined in some detail changes in magnetisation on these minor loops and we infer that these are changes in the irreversible component of magnetisation. Such changes are anomalous as the sample is maintained in a negative field at all times. We have also observed time dependent changes in magnetisation in which M increases in a positive sense in a negative field. Analysis of this effect shows that it alone is insufficient to account for the eye effect. We discuss the origins of the eye effect in terms of interaction effects in materials and show that this phenomenon can occur in dipolar and exchange coupled materials and may provide a technique for probing local interaction effects.     

Photo-induced bias of the hysteresis loop in ferrites at room temperature with long-time memory

New photo-magnetic effects with an indefinitely long-time memory are found at room temperature in the epitaxial Mg_0.75Mn_0.21Co_0.04Fe₂O₄ ferrite film. Illumination of the ferrimagnetic material with low-intensity (0.4 W cm⁻²) circularly polarized light with or without a static magnetic field in the Faraday effect geometry results in a number of nonlinear effects in both space and time. In a uniform crystal with cubic symmetry, the long-lived photo-induced magnetization (PIM) with a unidirectional anisotropy appears along the direction of the incoming light. The effects depend on a combination of magnetic field H and the helicity of circularly polarized light σ. Two combinations H⁺,σ⁺ and H⁻,σ⁻ lead to a photo-induced unidirectional anisotropy with a shift of the hysteresis loop along an applied field and a change in loop parameters. The loop contracts by a factor of two, the shift of the mid-point H_sh increases by factor of five surpassing the coercivity H_c, the coercivity H_c1 and remanence M_r1 (for decreasing applied field) reverse the sign, increasing by 9 Oe and reducing by a factor of 4.5, respectively. The effects cannot be erased by a conventional demagnetization (using an AC current that is reduced to zero amplitude), but can be removed using an illumination with two other combinations (H⁺,σ⁻ and H⁻,σ⁺) as well as by heating at temperatures higher than the Curie temperature. This long-lived room-temperature memory effect may arise from the formation of complex photo-induced defects including photo-induced magnetic polarons. The possible mechanisms responsible for the appearance of a room-temperature photo-induced unidirectional anisotropy with a long-lived memory are discussed. These new photo-magnetic effects may find an application in magneto-optical memory devices.     

The hysteresis loop of two-phase particulate magnetic composite with non-linear hard magnetic components

The method of calculating the B - H curve of two-phase ferromagnetic composite materials whose components have B - H relations of the form B = mH + Br is extended to include materials whose components have non-linear B - H relations. The functional form of the non-linear B - H curve of the components materials is simulated by hyperbolic tangent functions with adjustable parameters. The result of theoretical calculations are compared to experimental data on Mn-Al-C and Fe-Cr-Co particulate composites. Good agreement are obtained.     

高阶多项式在拟合铁磁物质磁滞回线中的应用

探讨用不小于三阶的多项式去拟合磁滞回线,完成只用2个多项式拟合整个回线.区别于其他人提出的实际上是利用二次多项式达到的一条曲线分2段、整个回线分4段的拟合.     

从磁滞回线了解铁磁性材料的性能

从磁滞回线简要讨论了铁磁性材料的性能及特点,并指出一些大学物理教材在这方面讨论的不妥之处.     

On the question of the influence of magnetic after-effect on the frequency dependence of the complex permeability

It is shown that the relations generally used for interpreting the frequency dependence of complex susceptibility caused by magnetic after-effect differ from those obtained by consistent application of the Néel theory. These more exact expressions are derived and it is shown that they represent the measured dependence better.     

On the influence of the magnetic diffusion after-effect on the complex susceptibility. — The logarithmic distribution of time constants

The general formula for complex initial susceptibility has been derived from the Néel theory of the magnetic diffusion after-effect in the case of the continuous distribution of time constants. The influence of the logarithmic distribution on the frequency dependence of the complex susceptibility and the temperature dependence of the loss-factor is examined in detail. The theoretical and experimental curves, tanδ vs.T, of three ferrite samples are compared.