Dimensionality crossovers in the magnetization of the weakly ferromagnetic two-dimensional manganese alkylphosphonate hydrates MnCnH2n+1PO3.H2O, n=2-4

Abstract

Critical exponents of magnetization beta below T_N in the weakly ferromagnetic layer compounds MnC_nH_2n+1PO₃.H₂O have been measured by SQUID magnetometry for n=2-4. In all three compounds crossovers are observed in beta as follows ( beta ₁, beta ₂): 0.21(2), 0.73(2) (n=2); 0.18(1), 0.42(6) (n=3), 0.18(1), approximately 0.6 (n=4). The crossover occurs at values of the reduced temperature epsilon =(T_N-T)/T_N that become smaller as the separation between the magnetic layers increases.