Effect of impurities on the Néel temperature and the low-temperature magnetic susceptibility of the quasi-one-dimensional antiferromagnet TMMC

Low-temperature magnetic susceptibility and Néel-temperature measurements of tetramethylammonium trichloromanganate (TMMC) doped by different impurities, Cd, Cu, Co, and Ni, are reported. For TMMC: Cd, an additional susceptibility proportional to $T^{-1\mathrm{}}$ above $T_N$ and a drastic reduction of $T_N$ by a factor of 2 for Cd concentration as low as 0.5 at.% have been observed. These features are well explained by assuming complete breaking of the Mn antiferromagnetic chains. Both susceptibility and $T_N$ measurements in TMMC with magnetic impurities have demonstrated the existence of an impurity-Mn interaction $J_1$ and allowed its estimation: $J_{1\mathrm{C}\mathrm{u}-\mathrm{M}\mathrm{n}}=1.4\mathrm{}$ K and $\left|J_{1\mathrm{N}\mathrm{i}-\mathrm{M}\mathrm{n}}\right|=1.9\mathrm{}$ K. We give experimental evidence of the $\mathrm{XY}$ behavior of the one-dimensional correlations at low temperature.