Universality in the temperature dependence of the heat capacity of magnetic solids

Authors : Ulrich Köbler

Pages : 147-174

Doi:10.5541/ijot.756405

View : 8 | Download : 4

Publication Date : 2020-08-27

Article Type : Research

Abstract :It is shown that the temperature dependence of the heat capacity of the magnetic solids can completely be described by a sequence of universal power functions of temperature. Characteristic for universality is that each power function holds over a finite temperature range and has a rational exponent. The analytical change from one to the adjacent power function is a typical crossover event. Universality reveals that the temperature dependence of the heat capacity is determined by a boson field whereas the absolute values are given by all magnetic and non-magnetic inter-atomic interactions. Universality for temperatures outside the critical range at Tc, i.e. for temperatures for which the phonons dominate the heat capacity has to be characterized as non-intrinsic, arising from interactions of the phonons with the bosons of the continuous magnetic medium. As we have shown earlier, the bosons of the continuous magnetic solid are essentially magnetic dipole radiation generated via stimulated emission by the precessing spins. We have called them Goldstone bosons. The interactions of the Goldstone bosons with the magnons modify the wave-vector dependence of the magnons. For cubic crystals the dispersions along [ζ, 0, 0] direction are essentially as for the linear spin chain, i.e. one-dimensional. As the different rational exponent values in the temperature power function of the heat capacity show, there exists a number of distinct modes of interaction between the Goldstone boson field and the phonons. The actual exponent depends additionally on the proportion between the magnetic and the non-magnetic energy contributions and therefore changes with temperature. The observed exponents are, however, difficult to interpret.
Keywords : Ordered boson fields, Magnetic domain patterns