3.024 Electrical, Optical, and Magnetic Properties of Materials Spring 2012 Recitation 14 Outline:
... To get the full picture, we must use quantum mechanics, which means using operators. ...
... To get the full picture, we must use quantum mechanics, which means using operators. ...
Lecture 29
... Curie law, which is χ = ρ μ2/kT, where μ is the effective moment of the electrons. (This sometimes differs somewhat from μB.) The temperature dependence comes from the fact that temperature tends to randomize the spins. This effect competes with the aligning effect of the field. The result is the Cu ...
... Curie law, which is χ = ρ μ2/kT, where μ is the effective moment of the electrons. (This sometimes differs somewhat from μB.) The temperature dependence comes from the fact that temperature tends to randomize the spins. This effect competes with the aligning effect of the field. The result is the Cu ...
12/06/05
... Recall why we have FM in metals: • Band structure leads to enhanced exchange interactions between (relatively) localized spins (d- or f-shell electrons). • Conduction electrons can play a very important role. In semiconductors, • Carriers present are only there because of doping, and at much lower c ...
... Recall why we have FM in metals: • Band structure leads to enhanced exchange interactions between (relatively) localized spins (d- or f-shell electrons). • Conduction electrons can play a very important role. In semiconductors, • Carriers present are only there because of doping, and at much lower c ...
Curie temperature
Curie point, also called Curie Temperature, temperature at which certain magnetic materials undergo a sharp change in their magnetic properties. In the case of rocks and minerals, remanent magnetism appears below the Curie point—about 570° C (1,060° F) for the common magnetic mineral magnetite. This temperature is named for the French physicist Pierre Curie, who in 1895 discovered the laws that relate some magnetic properties to change in temperatureIn physics and materials science, the Curie temperature (Tc), or Curie point, is the temperature where a material's permanent magnetism changes to induced magnetism. The force of magnetism is determined by magnetic moments.The Curie temperature is the critical point where a material's intrinsic magnetic moments change direction. Magnetic moments are permanent dipole moments within the atom which originate from electrons' angular momentum and spin.Materials have different structures of intrinsic magnetic moments that depend on temperature. At a material's Curie Temperature those intrinsic magnetic moments change direction.Permanent magnetism is caused by the alignment of magnetic moments and induced magnetism is created when disordered magnetic moments are forced to align in an applied magnetic field.For example, the ordered magnetic moments (ferromagnetic, Figure 1) change and become disordered (paramagnetic, Figure 2) at the Curie Temperature.Higher temperatures make magnets weaker as spontaneous magnetism only occurs below the Curie Temperature. Magnetic susceptibility only occurs above the Curie Temperature and can be calculated from the Curie-Weiss Law which is derived from Curie's Law.In analogy to ferromagnetic and paramagnetic materials, the Curie temperature can also be used to describe the temperature where a material's spontaneous electric polarisation changes to induced electric polarisation or the reverse upon reduction of the temperature below the Curie temperature.The Curie temperature is named after Pierre Curie who showed that magnetism was lost at a critical temperature.