Coercivity global model and magnetization reversal in fine hexaferrites

Abstract

In this work, the so‐called global model for magnetization reversal is applied to describe the coercive field temperature dependence in fine barium and strontium M‐hexaferrites (75–300 K range). Using magnetic viscosity measurements, the temperature dependence of the activation volume for magnetization reversal was obtained. In this temperature range, the coercive field (as the anisotropy field) increases with increasing temperature. However, it is found experimentally that the activation volume also increases with temperature and then the physical interpretation of the model is partially not clear.

Coercivity, Activation Volumes, and Interactions in BaFe12O19

“…It is, however, different from the premise of the Givord model that assumes that the moment configuration within the initial nucleus must have necessarily similarities with a magnetic domain wall. [15,[31][32][33][34] Then, further studies are necessary to analyze if true nucleation is the determinant mechanism in these samples and the physical interpretation of the Givord model.…”

“…For remanence curves measurements and ΔM technique, the method due to by Kelly et al [36][37][38] was used, see refs. [14,15] for more details. The magnetic viscosity measurements were carried out with the procedure that can be seen detailed in ref.…”

“…[8][9][10][11][12][13] Despite these novel properties, in M hexaferrites there are open issues associated to mechanisms of magnetization reversal and magnetic relaxation. [14][15][16] As the grain size is reduced and multidomain state becomes unfavorable, magnetization reversal must occur by coherent or incoherent processes and therefore aspects such as interparticle interactions come to be more important. In relation to that, a study on SrFe 12 O 19 (Sr-M) samples prepared using different methods was previously reported.…”

Coercivity and Interactions in Sr–M Thin Films with Nonperpendicular Orientation

“…Lately, magnetoelectric effects have also been encountered in thin films of substituted M‐type hexaferrites, adding more interest in this particular topic . Even though these novel magnetoelectric effects were published recently, in M hexaferrites films and also in bulk samples, there is not yet an exhaustive description on other important phenomena such as mechanisms of reversal magnetization in fine particle samples and magnetic viscosity . This sample constituted interesting systems for the study of particle interactions because they are formed mainly by hexagonal platelets with their easy axis of magnetization perpendicular to the hexagonal plane.…”

“…[13][14][15] Even though these novel magnetoelectric effects were published recently, in M hexaferrites films and also in bulk samples, there is not yet an exhaustive description on other important phenomena such as mechanisms of reversal magnetization in fine particle samples and magnetic viscosity. [16] This sample constituted interesting systems for the study of particle interactions because they are formed mainly by hexagonal platelets with their easy axis of magnetization perpendicular to the hexagonal plane. A preview report on these topics has already been published but in bulk samples obtained by the ceramic and chemical coprecipitation methods.…”