2ND-ORDER UNIFORM DYNAMIC SUSCEPTIBILITY OF LIGHTLY OXYGENATED LA2O4-CRYSTALS AND PECULIARITY OF THEIR MAGNETIC-PROPERTIES AT PHASE-SEPARATION(X SINGLE)

We report a study of the second order dynamic susceptibility in parall el static and alternating magnetic fields of three lightly oxygenated single crystals of La2CuO4+x(x<0.03) with different T-N(T-N1=222 K, T- N2=272 K and T-N3=243K). The response of all the samples reveals commo n features which are characteristic of an antiferromagnet with a weak ferromagnetism (WF). These new magnetic properties are attributed to t he oxygen-rich phase forming in the course of the phase separation. We show that the WF can be related to out-of CuO2 plane ordering (stagin g) of the interstitial oxygen. The response of crystals N1 and N3 is o bserved in the vicinity of T-N and exhibits a critical enhancement. A simple model of WF domain is presented which allows us to describe qua ntitatively the H-dependence of the signal of crystal N3 above T-N. It provides a basis for a comparative analysis of the data on N1 and N3 crystals. The response of crystal N2 is found below T-N. In this case its peculiarities reflect change and destruction of initial magnetic o rdering in the forming oxygen-rich phase.