Spin Temperature

spin temperature

[′spin ‚tem·prə·chər]
(solid-state physics)
For a system of electron spins in a lattice, a temperature such that the population of the energy levels of the spin system is given by the Boltzmann distribution with this temperature.

Spin Temperature

 

a quantity that characterizes the distribution of paramagnetic particles (particles with spin) among the magnetic sublevéis formed when the particles’ levels are split in a magnetic field (seeZEEMAN EFFECT). In equilibrium, the distribution can be described by the equation (seeBOLTZMANN STATISTICS)

n(ℰ) = Cexp(– ℰ/kTs)

Here, n(ℰ) is the number of particles with energy ℰ, C is a con stant, k is the Boltzmann constant, and Ts is the spin temperature. A state of internal equilibrium in a system of paramagnetic particles and, consequently, a spin temperature differing from the lattice temperature are established only if the energy exchange within the system of particles (spin-spin relaxation) occurs more rapidly than the energy exchange between the paramagnetic particles and the crystal lattice (spin-lattice relaxation). The spin temperature may be not only positive but negative. A negative spin temperature corresponds to an inversion of the populations of the energy levels (seeQUANTUM MECHANICALAMPLIFIER).

A. V. FRANTSESSON

References in periodicals archive ?
Because more nuclei are in the high-energy state than in the low-energy state, the nuclei are said to have a negative spin temperature.