Random field and random anisotropy effects in defect-free three-dimensionalXYmodels

Abstract

Monte Carlo simulations have been used to study a vortex-free XY ferromagnet with a random field or a random anisotropy on simple cubic lattices. In the random field case, which can be related to a charge-density wave pinned by random point defects, it is found that long-range order is destroyed even for weak randomness. In the random anisotropy case, which can be related to a randomly pinned spin-density wave, the long-range order is not destroyed and the correlation length is finite. In both cases there are many local minima of the free energy separated by high entropy barriers. Our results for the random field case are consistent with the existence of a Bragg glass phase of the type discussed by Emig, Bogner and Nattermann.

Critical properties of random anisotropy magnets

“…Moreover, another Monte Carlo study of the RAM with m = 2 and the same relation between J and D obtained critical exponents with values similar to the XY -ferromagnetic transition, except that the heat capacity critical exponent was found to be positive [68]. It was shown that the long-range order is not destroyed in the vortex-free model with p−fold fields [67].…”

Scaling of coercivity in a 3d random anisotropy model

“…[13] The same concept was applied to other systems, such as superfluid 3He-A in aerogel. [14] There has also been analytical work accompanied by Monte Carlo studies on small lattices [15,16,17,18] which assumed thermal equilibrium.…”

Reentrant Spin-Glass Transition in a Dilute Magnet

“…The FM order, which grows at higher temperatures, vanishes because of a random field effect [11]. Later, it was pointed out that not random field but random anisotropy brings a RSG-like phenomenon [12,13]. In a FM model with random anisotropy, as the temperature is decreased from a high temperature, there first appears a correlated SG (CSG) phase that is characterized by a well developed FM spin correlation.…”