FIGURE 36.4 Quantum mechanical exchang es cause a parallel arrar of materials for which the ratio of atomic separation, D, is at least 1.5 x d, the diamter of the 3d orbita Intrinsic Magnetic Properties Intrinsic magnetic properties are those properties that depend on the type of atoms and their composition and rystal structure, but not on the previous history of a particular sample. Examples of intrinsic magneti properties are the saturation magnetization, Curie temperature, magnetocrystallic anisotropy, and magneto- striction Extrinsic magnetic properties depend on type, composition, and structure, but they also depend on the previous history of the sample, e.g., heat treatment. Examples of extrinsic magnetic properties include the technologically important properties of remanent magnetization, coercivity, and permeability. These properties can be substantially altered by heat treatment, quenching, cold-working the sample, or otherwise changing the ze of the magnetic particle A ferromagnetic or ferrimagnetic material, on being heated, suffers a reduction of its magnetization(per unit mass, i. e, O, and per unit volume, M). The slope of the curve of M, vS. T increases with increasing temperature as shown in Fig. 36.5. This figure represents the conflict between the ordering tendency of the exchange interaction and the disordering effect of increasing temperature. At the Curie temperature, the order no longer exists and we have a paramagnetic material. The change from ferromagnetic or ferrimagnetic materials to paramagnetic is completely reversible on reducing the temperature to its initial value. Curie temperatures are always lower than melting points le crystal of iron has the body-centered structure at room temperature. If the magnetization as a function of applied magnetic field is measured, the shape of the curve is found to depend on the direction of ature, and the"easy" directions of magnetization are those directions parallel to the cube edges [100],[010 and [001] or, collectively, <100>. The hard direction of magnetization for iron is the body diagonal [111].At higher temperatures, the anisotropy becomes smaller and disappears above 300C 3. Nickel crystals(face-centered cubic) have an easy direction of [111] and a hard direction of [100]. Cobalt has the hexagonal close-packed (HCP)structure and the hexagonal axis is the easy direction at room temperature Magnetocrystalline anisotropy plays a very important part in determining the coercivity of ferro- or ferri- magnetic materials, i.e., the field value at which the direction of magnetization is reversed. Many magnetic materials change dimensions on becoming magnetized: the phenomenon is known a magnetostriction and can be positive, i. e, length increases, or negative. Magnetostriction plays an important role in determining the preferred direction of magnetization of soft, i. e, low H, films such as those of alloys of nickel and iron, known as Permalloy The origin of both magnetocrystalline anisotropy and magnetostriction is spin-orbit coupling. The magnitude of the magnetization of the film is controlled by the electron spin as usual, but the preferred direction of that e 2000 by CRC Press LLC© 2000 by CRC Press LLC Intrinsic Magnetic Properties Intrinsic magnetic properties are those properties that depend on the type of atoms and their composition and crystal structure, but not on the previous history of a particular sample. Examples of intrinsic magnetic properties are the saturation magnetization, Curie temperature, magnetocrystallic anisotropy, and magneto￾striction. Extrinsic magnetic properties depend on type, composition, and structure, but they also depend on the previous history of the sample, e.g., heat treatment. Examples of extrinsic magnetic properties include the technologically important properties of remanent magnetization, coercivity, and permeability. These properties can be substantially altered by heat treatment, quenching, cold-working the sample, or otherwise changing the size of the magnetic particle. A ferromagnetic or ferrimagnetic material, on being heated, suffers a reduction of its magnetization (per unit mass, i.e., s, and per unit volume, M). The slope of the curve of Ms vs. T increases with increasing temperature as shown in Fig. 36.5. This figure represents the conflict between the ordering tendency of the exchange interaction and the disordering effect of increasing temperature. At the Curie temperature, the order no longer exists and we have a paramagnetic material. The change from ferromagnetic or ferrimagnetic materials to paramagnetic is completely reversible on reducing the temperature to its initial value. Curie temperatures are always lower than melting points. A single crystal of iron has the body-centered structure at room temperature. If the magnetization as a function of applied magnetic field is measured, the shape of the curve is found to depend on the direction of the field. This phenomenon is magnetocrystalline anisotropy. Iron has body-centered structure at room temper￾ature, and the “easy” directions of magnetization are those directions parallel to the cube edges [100], [010], and [001] or, collectively, <100>. The hard direction of magnetization for iron is the body diagonal [111]. At higher temperatures, the anisotropy becomes smaller and disappears above 300°C. Nickel crystals (face-centered cubic) have an easy direction of [111] and a hard direction of [100]. Cobalt has the hexagonal close-packed (HCP) structure and the hexagonal axis is the easy direction at room temperature. Magnetocrystalline anisotropy plays a very important part in determining the coercivity of ferro- or ferri￾magnetic materials, i.e., the field value at which the direction of magnetization is reversed. Many magnetic materials change dimensions on becoming magnetized: the phenomenon is known as magnetostriction and can be positive, i.e., length increases, or negative. Magnetostriction plays an important role in determining the preferred direction of magnetization of soft, i.e., low Hc, films such as those of alloys of nickel and iron, known as Permalloy. The origin of both magnetocrystalline anisotropy and magnetostriction is spin-orbit coupling. The magnitude of the magnetization of the film is controlled by the electron spin as usual, but the preferred direction of that FIGURE 36.4 Quantum mechanical exchange forces cause a parallel arrangement of the spins of materials for which the ratio of atomic separation, D, is at least 1.5 ¥ d, the diamter of the 3d orbital