Freezing of anisotropic spin clusters in La1.98Sr0.02CuO4

A spin-glass compound, La1.98Sr0.02CuO4, shows quasi-three-dimensional magn etic ordering below similar to 40 K. A remarkable feature is that the magne tic correlation length along the orthorhombic a(ortho) axis is much longer than that along the b(ortho) axis, suggesting that the spin structure is cl osely related to the diagonal stripe structure. The spin-glass state can be expressed as a random freezing of quasi-three-dimensional spin clusters wi th anisotropic spin correlations (xi(a)'similar to 160 Angstrom, xi(b)'simi lar to 25 Angstrom, and xi(c)'similar to 4.7 Angstrom at 1.6 K). The new ma gnetic state is important as an intermediate phase between the three-dimens ional antiferromagnetic ordered phase in La2CuO4 and the incommensurate pha se in La1.95Sr0.05CuO4 in which the positions of the incommensurate peaks a re rotated by 45 degrees in reciprocal space about (pi, pi) from those obse rved in the superconducting La2CuO4 compounds.