Ferromagnetic, diamagnetic and paramagnetic properties. Magnetic hysteresis. Domain structure. скачать в хорошем качестве

Ferromagnetic, diamagnetic and paramagnetic properties. Magnetic hysteresis. Domain structure.

Paramagnets and diamagnets Any substance is a magnet, that is, it is capable of acquiring a magnetic moment (be magnetized) under the action of a magnetic field. An orbiting electron, like a closed current, is affected by a torque in a magnetic field. As a result, the electron receives an additional uniform rotation, in which the angular momentum vector L large will describe a cone around the direction of induction B with some angular velocity omega. This movement is called precession. Substances that are magnetized in an external magnetic field against the direction of the field are called diamagnets (for example, Ag Argentum Silver, Au Aurum gold, Cu Cuprum copper). Diamagnetism is inherent in all substances. Since under the action of an external magnetic field on the electrons of atoms of a substance, an own magnetic field of the substance is formed, which weakens the external magnetic field Paramagnetic substances - substances that are magnetized in an external magnetic field in the direction of the field (example: rare earth metals, Pt Platinum platinum, Al Aluminum aluminum). Magnetization. Magnetic field in matter For a quantitative description of the magnetization of magnets, a vector quantity is introduced - the magnetization, determined by the magnetic moment per unit volume of the magnet: The magnetization vector J is equal to the ratio of the vector of the magnetic moment of the magnet p with index m to the volume V or is equal to the ratio of the sum of individual magnetic moments p with index a to volume V, where p with index m is equal to the sum of individual magnetic moments p with index a is the magnetic moment of the magnet, equal to the vector sum of the magnetic moments of individual molecules. In weak fields, the magnetization J is proportional to the strength H of the field causing the magnetization. CI is the magnetic susceptibility of a substance: a dimensionless quantity. For diamagnets, CI is negative (Xi is less than zero, the field of molecular currents is opposite to the external field), and for paramagnets CI is positive (Xi is greater than zero, the field of molecular currents coincides with the external one). The absolute value of the magnetic susceptibility for diamagnets and paramagnets is very small, on the order of 10–4 – 10–6. 10 minus 4 - 10 minus 6 The magnetic permeability of the substance MU is equal to unity plus the susceptibility Xi and is equal to the ratio of the magnetic induction in the substance to the magnetic field in vacuum. The dimensionless quantity is called the magnetic permeability of a substance. The magnetic field B is equal to the product of the zero magnetic constant mu, the magnetic permeability mu and the magnetic field strength H. For diamagnets, mu is less than one, for paramagnets, mu is greater than one. Ferromagnets and their properties In addition to weakly magnetic substances - diamagnets and paramagnets, there are strongly magnetic substances - ferromagnets - substances that have spontaneous magnetization, that is, they retain magnetization in the absence of an external magnetic field. Unlike weakly magnetic substances, in which the magnetization J changes linearly with increasing H, in ferromagnets, with increasing H, the magnetization grows rapidly at first, and then reaches saturation of us J. Magnetic Hysteresis The dependence of the magnetization J on the magnetic field strength H in a ferromagnet is determined by the prehistory of magnetization. This phenomenon is called magnetic hysteresis. If a ferromagnet is magnetized to saturation (curve 0–1), and then H is reduced (curve 1–2), then at H=0, the residual magnetization J remains in the ferromagnet. This phenomenon is used in the manufacture of permanent magnets. In order to reduce the magnetization to zero, it is necessary to apply an oppositely directed field (point 3), with a strength H with index c, which is called the coercive force. With a further increase in the opposite field, the ferromagnet remagnetizes (curve 3–4), reaching saturation (point 4). Then it can be again demagnetized (curve 4–5–6) and again remagnetized to saturation (curve 6–1). Thus, the change in magnetization is described by a 1-2-3-4-5-6-1 curve, which is called a hysteresis loop. Domain structure. For each ferromagnet, there is a certain temperature, called the Curie point, at which it loses its magnetic properties. When heated above the Curie point, a ferromagnet transforms into an ordinary paramagnet. A ferromagnet is divided into a large number of microscopic regions - domains, spontaneously magnetized to saturation. The external field orients the magnetic moments of entire regions of spontaneous magnetization along the field, and the domains turn abruptly along the field.