Spin-flop State Research Articles

Spin-Flop Domains in MnF2

An intermediate state is shown to exist between the antiferromagnetic and spin-flop states of antiferromagnetic Mn${\mathrm{F}}_{2}$. This state consists of alternate thin-slab domains of antiferromagnetic and spin-flop material. Experimental evidence includes NMR, Faraday rotation, optical-absorption spectroscopy, and photographs of the domain structure. A molecular field model is used to calculate the field width of the domain region and the physical width of the domains. Reasonable numerical agreement is found.

Off-Diagonal Long-Range Order in Solids

The possibility of the coexistence of the diagonal long-range order (DLRO) and the off-diagonal long-range order ( ODLRO), which may be called 'supersolid' state, is discussed in a system of bosons at 0°K. Examples of wave functions are given de­ scribing the state with only DLRO and with both DLRO and ODLRO. After giving general relationships between the quantum lattice model for a system of bosons and the corresponding spin system, the criterion for the coexistence of DLRO and ODLRO is obtained by using the molecular field approximation for the spin system. The super­ solid state corresponds to an 'intermediate' state between the antiferromagnetic and spin-flop state in the spin system. The analysis on the basis of this criterion indicates that the bulk solid He 4 is unlikely to become a supersolid, whereas the adsorbed He 4

Spin Configurations in an Antiferromagnetic Slab

The low-energy spin configurations of a two sublattice antiferromagnet have been examined for a sample of finite thickness. The model consists of layers of spins connected by isotropic nearest-neighbor exchange interactions. The applied field and the anisotropy field are assumed to be perpendicular to the layers; the molecular-field approximation is used to relate the orientations of the spins within a layer. The equilibrium equations and boundary conditions are found as a continuum limit of difference equations obtained by minimizing the energy with respect to the directions of the spins. It is found that a nonuniform spin configuration has a lower energy than the uniform antiferromagnetic state for applied fields above (2)−1/2Hc, where Hc is the critical field for the spin-flop transition that occurs in the usual treatment of the two sublattice model. In the new equilibrium state, the spins at the center of the slab are arranged in a spin-flopped configuration. At applied fields well below Hc, the configuration rapidly approaches the antiferromagnetic state with increasing distance away from the center of the slab. As the applied field is increased through Hc, the width of the ``flopped'' region near the center increases rapidly and the configuration approaches a uniform spin-flop state except in the regions near the surface. It is found that the surface spin-flop state1 does not occur as an equilibrium solution of the problem if all important contributions to the difference equations are retained.