Spin waves energy gap

Lounasmaa and Sundstrom (1966), in view of the strong basal plane anisotropy of Tb at low temperatures, favoured introduction of a spin-wave energy gap as against a simple power law for Cm. They found a reasonable fit with Cm = 36 r exp(-23.5/T) from 8 to 20 K, based on the assumption Ce+Cl = Cp (Lu). In their analysis, Wells et al. (1976) used a theoretical expression... 

In the case of Tb, the most systematic data for kI T) are those of Feron et al. deduced from measurements of the c-axis magnetization leading to k2(0) = 9.0 1.8 X 10 Jm From the zero-torque method, Rhyne and Clark estimated K2(0) = 8.7 2.2 X idi Jm . In their analysis of the spin wave energy gap in Tb (section 2.1.1) Roeland et al. (1975) derived a value (0.23 meV/ion) for the microscopic parameter Using eq. 6.42, this result is equivalent to k (0) = 7.6xlO Jm, in agreement with the macroscopic values within experimental error. 

The significance of the spin wave energy gap (A) for the transport properties of anisotropic ferromagnets was first recognized by Mackintosh 1963), who... 

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