Spin-glass freezing in Kondo-lattice compounds - art. no. 054409

A theory is presented that describes a spin-glass phase at finite temperatu res in Kondo-lattice systems with an additional Ruderman-Kittel-Kasuya-Yosi da interaction represented by long range, random couplings among localized spins as in the Sherrington-Kirkpatrick (SK) spin-glass model. The problem is studied within the functional integral formalism where the spin operator s are represented by bilinear combinations of fermionic (anticommuting) Gra ssmann variables. The Kondo and spin-glass transitions are both described w ith the mean-field-like static ansatz that reproduces good results in the t wo well-known limits. At high temperatures and low values of the Kondo coup ling there is a paramagnetic (disordered) phase with vanishing Kondo and sp in-glass order parameters. By lowering the temperature, a second order tran sition line is found at T-SG to a spin-glass phase. For larger values of th e Kondo coupling there is a second order transition line at roughly T-k to a Kondo ordered state. For T<T-SG, the transition between the Kondo and spi n-glass phases becomes first order.