Due to shape anisotropy, magnetization prefers to be along the long axis as in (a). Its microstructure consists of fine elongated Fe-Co rich particles, called the «’-phase, dispersed in a matrix that is Ni-Al rich and called the a-phase. Ferromagnetic materials include iron, nickel, cobalt and (most of) their alloys (an alloy is a mixture of a metal and another element), such as steel. The particles are magnetically hard because they are sufficiently small for each to be of single domain or they possess substantial shape anisotropy (elongated particles may be ferromagnetic alloys, e. g., Fe-Co, or various hard ferrites). Thus the coercivity is high. mercury, lead, sulfur, copper, silver, bismuth, wood etc., are known as diamagnetic materials. This energy density (J m-3) in the external field depends on the maximum value of the product BH in the second quadrant of the B-H characteristics and is denoted as (BH)m3iX. Diamagnetism is a fundamental property of all matter, although it is usually very … Magnetically hard materials are used to create permanent magnets made from alloys generally consisting of varying amounts of iron, aluminium, nickel, cobalt and rare earth elements samarium, dysprosium and neodymium. It corresponds to the largest rectangular area that fits the B-H curve in the second quadrant, as shown in Figure 8.39. Figure 8.41 A single domain elongated particle. Ferromagnetism: Ferromagnetic materials can form permanent magnets and are attracted to magnets. The magnetic susceptibility χ is small and +ve. These materials have low retentivity. To reverse the magnetization from +z to — z by an applied field, we have to rotate the spins around past the hard direction, as shown in Figure 8.40, since we cannot generate reverse domains (or move domain walls). A magnetic field is the invisible area around a magnet where magnetism occurs. The tetragonal crystal struc­ture has the easy direction along the long axis and possesses high magnetocrystalline anisotropic energy. Soft Magnetic Materials 2. Those materials which when placed in a magnetic field become weakly magnetized in a direction opposite to that of the applied field, are called as diamagnetic materials. Soft-magnetic materials are mainly used in magnetic cores of transformers, motors, inductors, and generators. Materials which have magnetic moments arising from spin and orbital angular momentum of electrons are magnetic materials.The magnetic moment per unit volume is called magnetization or magnetic polarization, denoted by J.The magnetization is a vector quantity and its unit is Wb/m 2 or T (tesla). The critical size below which a particle becomes a single domain therefore increases with the crystalline anisotropy. If the magnetization M is along the long axis (along z), then the potential energy in the external magnetic field is less than if M were along the minor axis (along y), as com­pared in Figure 8.41a and b. The first known magnets are hard block stones called lodestone. Ampere’s law for H involves integrating H along a closed path or around the mean path length im + ig. exmaples of magnetic materials are iron,nickel,cobalt,paper clips,nails and some pins....:-). FREE Physics revision notes on Magnetic Materials. document.write(",

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