ORDERING OF MICROSCOPIC DZYALOSHINSKII-MORIYA VECTORS IN SPIN-GLASSES- STATICS AND LOW-FREQUENCY DYNAMICS

The mean-field theory of static and dynamic properties of the Dzyalosh inskii-Moriya (DM) interaction in Heisenberg spin glasses is developed . The main idea of the paper is based on the property of microscopic D M vectors D(ij) describing this interaction: each vector D(ij) is defi ned up to a sign. It is a reason for the existence of additional degre es of freedom connected with ordering of vectors D(ij) on orientations below the freezing temperature. The theory is formulated on the basis of the eigenmodes of the exchange integrals matrix J(ij). There are t wo additional important assumptions to define the model. The first one is the independence of the sum SIGMA(i) J(ij) from the index j that r estricts possible distributions of random exchange integrals. However, due to this assumption the total magnetization appears to be a hard e igenmode of the exchange part of the Hamiltonian and it is possible to a great extent to escape a detailed consideration of the spin-glass t ransition as well as to separate terms containing magnetization vector s in an equation for the thermodynamic potential in explicit form. The description of ordering of DM vectors D(ij) is carried out in terms o f some effective paramagnetic pseudospin, of which the state depends o n the thermodynamic path of the spin-glass sample. This property displ ays itself in the distinction between the field and zero-field-cooling susceptibility and in an appearance of the macroscopical unidirection al anisotropy field (the DM field). The second assumption is to consid er the DM field as a slow dynamical variable with a broad spectrum of relaxation times which, however, can behave as a quenched quantity at low enough temperatures. Motion equations of a dissipative character f or pseudospins are examined. Pseudospins corresponding to localized ei genmodes with characterizing size xi approximately 10(2) - 10(3) angst rom effectively contribute to observable slow relaxation. Using the dy namic susceptibility calculated the frequency dependence of freezing t emperature and the magnetization decay law are found.