We report a detailed study of the temperature and magnetic-field dependence of the spin susceptibility for a single crystal of ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\text{CuO}}_4$. From a quantitative analysis, we find that the temperature-dependent anisotropy of the susceptibility, observed in both the paramagnetic and stripe-ordered phases, directly indicates that localized Cu moments dominate the magnetic response. A field-induced spin-flop transition provides further corroboration for the role of local moments. Contrary to previous analyses of data from polycrystalline samples, we find that a commonly assumed isotropic and temperature-independent contribution from free carriers, if present, must be quite small. Our conclusion is strengthened by extending the quantitative analysis to include crystals of ${\text{La}}_{2-x}{\text{Ba}}_x{\text{CuO}}_4$ with $x=0.095$ and 0.155. On the basis of our results, we present a revised interpretation of the temperature and doping dependence of the spin susceptibility in ${\text{La}}_{2-x}{\left(\text{Sr},\text{Ba}\right)}_x{\text{CuO}}_4$.

• Received 6 November 2008

DOI:https://doi.org/10.1103/PhysRevB.78.214507