Materials have ease {permeability, magnetism}| {magnetic permeability} {mu, permeability} {µ, permeability} by which magnetic fields can go through. Permeability depends on ease with which magnetic dipoles form. Magnetic force constant k' directly depends on permeability.
types
Ferromagnetic materials have molecular magnetic fields that can align with outside magnetic field to enhance it. Non-magnetic materials and empty space have no magnetic fields and allow magnetic field. Diamagnetic materials have magnetic fields that oppose outside magnetic field. Paramagnetic materials have magnetic fields that slightly enhance outside magnetic field.
Crystals with impurities have greatly increased magnetization after crystal imperfections are overwhelmed by pressure {Barkhausen effect}.
Magnets cannot hold magnetism at high temperature {Curie temperature}, because random motions become great enough to cancel net magnetism.
In materials, all molecules in microscopic regions {domain, magnetism}| can have same magnetic-field alignment.
magnetization
After removing magnetization, domains return to original orientations {magnetic memory, domain}.
anistropy
Crystals magnetize differently on different axes {magnetocrystalline energy} {magnetocrystalline anisotropy}.
energy
Unaligned domains minimize magnetic-field potential energy {magnetostatic energy}. Boundaries between domains add potential energy {domain wall energy}. Domain-wall width increases by exchange energy but decreases by magnetocrystalline energy.
length
Crystals change length when magnetized, because domains shift {magnetostrictive energy}. Iron gets longer. Nickel gets shorter.
Electrical resistance can increase with increased magnetic field strength {extraordinary magnetoresistance} (EMR). Non-magnetic indium antimonide is a narrow gap semiconductor with high carrier mobility. Indium antimonide and gold lattice at room temperature has high EMR and so can be a magnetic-field sensor. Magnetic fields can change manganese oxide {manganite} from non-magnetic to ferromagnetic and metallic {colossal magnetoresistance} (CMR). Ferromagnetic layers with non-magnetic material between them {giant magnetoresistance} (GMR) are in disk-drive read heads.
External magnetic-field change changes material magnetization, after a time delay {hysteresis, magnetism}|. In motors and generators, external magnetic-field changes cycle, and material changes have time-delayed cycles {hysteresis loop}, with heat losses. Magnetic memory devices {twistor, memory} can use hysteresis loops.
Magnets can align all domains and have maximum magnetization {saturation, magnetism}|.
Magnetic materials {spin-glass} can have disordered magnetic domains that couple and make long-range effects.
5-Physics-Electromagnetism-Magnetism
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Date Modified: 2022.0225