Unusual magnetic susceptibility anisotropy in untwinned La2-xSr(x)CuO4 single crystals in the lightly doped region.

We present a study of the magnetic susceptibility chi in carefully detwinned La 2-xSr(x)CuO4 single crystals in the lightly doped region (x = 0-0.03), which demonstrates a remarkable in-plane anisotropy of the spin system. This anisotropy, chi(a)/chi(b), is found to persist after the long-range antiferromagnetic (AF) order is destroyed by hole doping, suggesting that doped holes break the AF order into domains in which the spin alignment is kept essentially intact. It turns out that the freezing of the spins taking place at low temperatures is also notably anisotropic, implying that the "spin-glass" feature is governed by the domain structure as well.