FIGURE 36.5 Ferro- and ferrimagnetic materials lose their spontaneous magnetic moment at temperatures above the Curie temperature, e saturation ment bie movement FIGURE 36.6 In soft magnetic materials domains form such that the total magnetization is zero. By applying small magnetic fields, domain walls move and the magnetization changes. magnetization with respect to the crystal lattice is determined by the electron orbits which are large enough to interact with the atomic structure of the film Extrinsic Magnetic Properties Extrinsic magnetic properties are those properties that depend not only on the shape and size of the sample, but also on the shape and size of the magnetic constituents of the sample. For example, if we measure the hysteresis loop like the one shown in Fig. 36.6 on a disk-shaped sample punched from a magnetic recording tape, the result will depend not only on the diameter and thickness of the disk coating but also on the distribution of shapes and sizes of the magnetic particles within the disk. They display hysteresis individually and collectively For a soft magnetic material, i e, one that might be used to make the laminations of a transformer, the dependence of magnetization, M, on the applied magnetic field, H, is also complex. Having once left a point described by the coordinates(H,, M), it is not immediately clear how one might return to that point. Alloys of nickel and iron, in which the nickel content is the greater, can be capable of a reversal of magne- tization by the application of a magnetic field, H, which is weaker than the earth's magnetic field(0.5 Oe, 40 A/m)by a factor of five. To avoid confusion caused by the geomagnetic field it would be necessary to screen the sample, for example, by surrounding it by a shield of equally soft material or by measuring the earths field e 2000 by CRC Press LLC© 2000 by CRC Press LLC magnetization with respect to the crystal lattice is determined by the electron orbits which are large enough to interact with the atomic structure of the film. Extrinsic Magnetic Properties Extrinsic magnetic properties are those properties that depend not only on the shape and size of the sample, but also on the shape and size of the magnetic constituents of the sample. For example, if we measure the hysteresis loop like the one shown in Fig. 36.6 on a disk-shaped sample punched from a magnetic recording tape, the result will depend not only on the diameter and thickness of the disk coating but also on the distribution of shapes and sizes of the magnetic particles within the disk. They display hysteresis individually and collectively. For a soft magnetic material, i.e., one that might be used to make the laminations of a transformer, the dependence of magnetization, M, on the applied magnetic field, H, is also complex. Having once left a point described by the coordinates (H1, M1), it is not immediately clear how one might return to that point. Alloys of nickel and iron, in which the nickel content is the greater, can be capable of a reversal of magne￾tization by the application of a magnetic field, H, which is weaker than the earth’s magnetic field (0.5 Oe, 40 A/m) by a factor of five. (To avoid confusion caused by the geomagnetic field it would be necessary to screen the sample, for example, by surrounding it by a shield of equally soft material or by measuring the earth’s field FIGURE 36.5 Ferro- and ferrimagnetic materials lose their spontaneous magnetic moment at temperatures above the Curie temperature, Qc. FIGURE 36.6 In soft magnetic materials domains form such that the total magnetization is zero. By applying small magnetic fields, domain walls move and the magnetization changes