Coupling constants magnetoelastic

In this section we present experimental results on the temperature dependence of elastic constants for intermetallic rare-earth compounds in which magnetoelastic effects due to the presence of crystal fields are dominant. There are systematic studies of these effects for given structures across the rare-earth series. Examples are the rare-earth monopnictides, especially the rare-earth antimonides (RSb), the rare-earth dialuminides (RAlj) and rare-earth compounds with the CsCl structure. From such experiments one obtains the single-ion magnetoelastic coupling constants gj. across the series and in a few cases the quadrupolar coupling constant gf [eq. (38)] too. The case of a cooperative Jahn-TeUer effect will be treated separately in sect. 2.4.3. The examples presented here can be explained mostly with the single-ion strain susceptibility Xr [ <1- (35) instead of eq. 

Bi = coefficients of operator equivalents in crystal field hamiltonian S = magnetoelastic coupling constant Bj(x) = Brillouin function B(q) = function entering spin-wave energy [see eq. (7.100)] e = (kT)- p = gmeHIkT c = c-axis lattice constant c = reciprical lattice constant C = basal plane elastic constant C] , C,-, = creation and annihilation operators for state m> on site 1 X = bulk susceptibility X, = atomic susceptibility x(d) - generalized wave number-dependent susceptibility function of conduction electrons... 

Calculations of magnetic behavior have been performed using the assumption that the elastic and magnetoelastic coupling constants in an epitaxial Er film are identical with those of bulk Er (Borchers et al. 1991). The calculation is able to explain the suppression of the ferromagnetic transition and to predict the critical magnetic field required to recover... 

The magnetoelastic coupling constants (in m K) of some LnSb phases (Mullen et al., 1974). Comparison of the experimental data with values calculated according to eq. (3.22) valid for the point-charge model with Z = —2 and (rr) values from Freeman and Watson (l%S). 

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