Thermal critical phenomena and crossover between critical regimes in ferromagnets with long-range interactions

Abstract

Abstract In this brief review, an attempt has been made to bring out clearly the role of long-range interactions (such as dipole – dipole interactions or isotropic exchange interactions decaying with interspin distance ‘r’ as J(r) ~ r –(d+σ) (0 < σ < 2), where ‘d’ is the space dimensionality) (i) in determining the thermodynamic properties of ferromagnets (in which the electrons responsible for magnetism are either localized or itinerant) in the asymptotic critical region, (ii) in causing a crossover from one critical regime to the other, and (iii) in stabilizing long-range magnetic order in site-diluted and/or bond-diluted ferromagnets with composition just above the percolation threshold. In the process, a number of long-standing/puzzling issues concerning the nature of magnetic order, static critical phenomena and crossover scenario in a wide variety of ferromagnetic systems have been resolved.