REVERSIBLE AND IRREVERSIBLE MAGNETIZATION IN SOFT IRON-BASED POLYCRYSTALLINE MATERIALS

The magnetization process has been investigated in nonoriented SiFe alloys over a wide induction range, from about 10(-4) T to technical saturation. Special attention has been devoted to the role of grain size <s>. The low-field behavior of the initial magnetization curve is characterized by a number of remarkable features: (1) the permeability mu-r tends, in the limit of vanishing applied field H, to a constant value, independent of <s>; (2) the increase of mu-r with H exhibits a nonlinear behavior, in contrast with the Rayleigh law; and (3) the larger the grain size, the steeper the rise of mu-r with H. This effect is attributed to an increased ease of propagation of locally induced magnetization reversals at larger <s> values. Experiments put in evidence a correlation between mu-r and the length of propagation lambda, which is found to vary as mu-r1/2. However, at high inductions (above about 1 T), larger grains imply a reduction of permeability, due to the growth of unfavorable crystallographic textures. Grain size also affects power losses to a large extent. Measurements performed at 1 and 1.5 T show that the hysteresis component P(h) and the excess eddy component P(e), respectively, vary as 1/ square-root <s> and square-root <s> in the investigated range 45-mu-m less-than-or-equal-to <s> less-than-or-equal-to 360-mu-m.