Development of Spin Correlations in Randomly Diluted Quasi-One-Dimensional Spin Systems

Abstract

The initial slope of the decreasing Néel temperature T_N(x), [d(T_N(x)⁄T_N(0))⁄dx]_x=0, in randomly diluted quasi-one-dimensional magnets (TMMC: Cu and (CH₃)₃NHCoCl₃·2H₂O: Mn or Cu) has been investigated down to the infinitesimal impurity concentration x; x=0.00041 in the case of TMMC: Cu. The development of spin correlation length ξ_1d(T) along the magnetic chain has been evaluated from the observed T_N(x) under zero or finite magnetic fields up to 30 kOe. It has been revealed that even a small amount of impurities which distribute each other with much longer separations than ξ_1d(T) give a substantial reduction of the development of ξ_1d(T). The rounding of the magnetic heat capacity peak around T_N(x) is discussed in terms of a new idea of “border concentration” which is characterized by the relation between the length of ξ_1d(T) and the inter-impurity distance.