Coercivity extrema in melt-spun CuCo ribbons: Effects of the magnetic moment distribution

Abstract

Measurements of magnetization loops on melt-spun CuCo ribbons revealed a minimum in the temperature dependence of the coercivity. A coherent interpretation was given through Monte Carlo simulations of a dispersed system of noninteracting, uniaxial magnetic granules embedded in a nonmagnetic matrix. The coercivity is implicitly defined by the balance between the negative magnetization of superparamagnetic granules and the remaining magnetization of blocked granules after saturation in the positive field direction. When the temperature rises in a system made of a large amount of small granules and a small amount of big granules, unblocking predominates over thermal fluctuations and the coercivity decreases until a certain temperature at which most of the small granules are superparamagnetic; above this temperature, thermal fluctuations predominate, and the coercivity increases almost linearly with the temperature until the final unblocking of the big granules.

Magnetism and Transport Properties of Sr2Ru1−xCoxO4 with x ≤ 0.25

“…Similar unusual H C – T relation is also found in the studies of M. A Novak's group on CoCu alloys where the H C ( T ) has a sharp decrease at first followed by an increase and a maximum around 100–200 K . According to their studies, this behavior is attributed to particle interactions, size distribution and a temperature‐dependent average blocking temperature . As the coercive fields of our samples are quite small, the superparamagnetism may indeed exist in them.…”

“…We attribute the new blocking temperature to the superparamagnetism in Sr 2 Ru 1 −x Co x O 4 , which coexists with the ferrimagnetism embedded in incommensurate AFM fluctuation. In the size distribution model, the unusual behavior of H C ( T ) is explained as follows: H C first decreases with the arising temperature, for numerous small granules are gradually unblocked; then, on account of the larger thermal fluctuations of the superparamagnetic moments, H C increases with temperature; at last, H C fades away for the granules are also unblocked . Similarly, we construct a phase separated state picture for Sr 2 Ru 1 −x Co x O 4 when x = 0.10–0.25 like this to interpret the corresponding abnormal H C – T relation: initially, the coercive field gradually decreases when we rise temperature from 5 K to around (10 K for Sr 2 Ru 0.85 Co 0.15 O 4 ), in which the superparamagnetic granules are gradually unblocked and ferrimagnetism is gradually weakened; then, coercive field increases due to the lager thermal fluctuations of the superparamagnetic moments, which covers the decrease in H C caused by weakening ferrimagnetism, and at 50 K H C becomes larger than that at 5 K; finally, the coercive field gradually vanishes above T B (75 K for Sr 2 Ru 0.85 Co 0.15 O 4 ) where the incommensurate fluctuations are also unblocked.…”

Thermal effects in a Stoner–Wohlfarth model and their influence on magnetic anisotropy determination

“…There have been numerous approaches to this problem using Monte Carlo simulation techniques [18][19][20][21][22]. An alternative way of tackling this problem has been to introduce the Neel relaxation approach inside the SW model.…”

“…Thermal activation effects on single domain fine magnetic particles has been studied by Monte Carlo simulations [18][19][20][21][22], and also some micromagnetic models exist for the study of their dynamical properties [23][24][25][26][27]. For a review on the subject see Ref.…”

Microstructure Evolution of Discontinuous Precipitation and Coarsening of Co Rod-like Precipitates in Supersaturated Cu-Co alloys

“…It is known that in diluted Cu-Co alloys, DP takes place at relatively low temperatures, ranging from 450 to 700°C with Co rod-like precipitates coherent with the matrix [1]. However, interesting magnetic properties have been reported in supersaturated Cu-Co alloys in condition in which DP is the dominant mode of precipitation after isothermal aging treatments [2,3]. For this reason, it is of fundamental importance to understand the development of DP and coarsening in CuCo alloys.…”