Disordered and Frustrated Spin Systems

Abstract

A brief review on the effects of quenched disorder on magnetic ordering is given. This disorder can be due to dilution of a ferro‐ or antiferromagnetic crystal with nonmagnetic atoms, or due to noncrystallinity (amorphous magnetic systems). This disorder in the positions of the magnetic atoms leads to disorder in the exchange interactions between spins. If the disorder is sufficiently weak, the critical temperature of magnetic ordering is somewhat decreased, and the critical behavior may change, but the nature of ordering is maintained. However, if the disorder is sufficiently strong, magnetic long‐range order may disappear altogether at a percolation threshold, or a new type of order may appear, the ‘spin glass’, in which spins freeze in random directions because of random competition between ferro‐ and antiferromagnetic interactions. In this context, we also mention magnetic systems with ‘frustration’ of their exchange interactions but without disorder. Finally, another important class of phenomena occurs for systems with ‘random fields’, an example of which is provided by diluted antiferromagnets in a uniform field.

Magnetization Plateaus at Low Temperature in a Triangular Spin Tube

“…This assumes the presence of a barrier concerning the magnetic excitations [31]. Similar behaviors were observed in a square spin-½ nanotube when diagonal exchange coupling is included [32], and in other frustrated systems [33,34]. Now, we present the dependence of total magnetization on external magnetic field for different temperatures for s = ½ and exchange anisotropy J' = -0, 5 in Fig.…”