Wall Jumps Research Articles

Space-time correlation properties of the magnetization process and eddy current losses: Applications. I. Fine wall spacing

The physical origin of eddy current losses in materials characterized by a very fine and complex domain structure is discussed, on the basis of a general statistical theory of losses developed in preceding papers. It is shown that the same process which is at the basis of the Barkhausen effect, namely the space-time clustering of elementary domain wall jumps, also gives rise to a detectable dynamic loss contribution in excess to the classical one, in spite of the fact that the ratio between the average wall spacing and the sample thickness is much smaller than unity. A quantitative evaluation of this effect is carried out, obtaining a loss equation which is then compared with some experimental data. Since, according to this interpretation, the same microscopic mechanism is responsible for both the Barkhausen effect and the loss anomaly, it is found that a quantitative relation exists between the parameters of the obtained loss expression and the Barkhausen noise statistical properties. Through this relation, a comparison of loss and Barkhausen noise measurements can provide a valuable test of the consistency of the proposed loss model.

Magnetic aftereffects in amorphous Co- and CoNi-based alloys after field annealing

The magnetic aftereffects and their dependence on annealing have been investigated for Fe 5Co 75B 20 and Co 55Ni 15Fe 5B 10Si 1 6. Relaxation effects of both periodic wall motion and wall jumps are observed. Stress-relief annealing with or without transverse or longitudinal fields decreases the relaxation, while annealing in a rotating field does not. In the first case, a frozen-induced magnetic anisotropy is observed by which the shape of the loops can be altered.

Barkhausen effect in magnetic thin films: General behaviour and stationarity along the hysteresis loop

Several aspects of the Barkhausen effect can be investigated by using a measurement equipment that records the Barkhausen signal as a function of time in digital form on computer tape. Measurements on thin magnetic films containing a small number of domain walls are presented. The behaviour of the wall jumps during a reversal is investigated. During the steep part of the loop the stationarity of the signal is measured with the magnetic field as a parameter. The influence of the coercive fieldH c and the thicknessd m is considered and compared with results obtained by others on bulk samples.

Barkhausen noise in amorphous ferromagnetic materials

Abstract Preliminary results on the Barkhausen noise spectra in amorphous magnetic ribbons as a function of sample shape and of temperature provide information on the clustering of Bloch wall jumps in these materials. A relation is found between noise intensity and core losses, which also suggests some hints for a new approach to the problem of anomalous excess losses in magnetic materials.

Influence of coercive force on low-frequency creep in bloch-wall permalloy films

A very high resolution Bitter pattern technique is used to observe the motion of Bloch walls in Permalloy films excited by slowly rising and slowly falling hard-axis fields. For low coercive force films, the basic motion consists of approximately equal and opposite jumps induced by simultaneous wall structure changes at two transition fields. Net motion begins with the application of small easy-axis bias fields. For high coercive force films, although the wall structure changes continue to occur, the wall jumps and a net displacement do net occur until the easy-axis bias field exceeds a certain critical value which is a function of the wall coercive force.