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arXiv · 1008.3523

Experimental determination of the Weiss temperature of Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH

Shiqi Li·Lin Bo·Bo Wen·M. P. Sarachik·P. Subedi·A. D. Kent·Y. Yeshurun·A. J. Millis·C. Lampropoulos·S. Mukherjee·G. Christou
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Abstract

We report measurements of the susceptibility in the temperature range from $3.5$ K to $6.0$ K of a series of Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH samples in the shape of rectangular prisms of length $l_c$ and square cross-section of side $l_a$. The susceptibility obeys a Curie-Weiss Law, $\chi=C/(T-\theta)$, where $\theta$ varies systematically with sample aspect ratio. Using published demagnetization factors, we obtain $\theta$ for an infinitely long sample corresponding to intrinsic ordering temperatures $T_c \approx 0.85$ K and $\approx 0.74$ K for Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH, respectively. The difference in $T_c$ for two materials that have nearly identical unit cell volumes and lattice constant ratios suggests that, in addition to dipolar interactions, there is a non-dipolar (exchange) contribution to the Weiss temperature that differs in the two materials because of the difference in ligand molecules.

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Shiqi Li, Lin Bo, Bo Wen, M. P. Sarachik, P. Subedi, A. D. Kent, Y. Yeshurun, A. J. Millis, C. Lampropoulos, S. Mukherjee, G. Christou. 2010-08-20. Experimental determination of the Weiss temperature of Mn$_{12}$-ac and Mn$_{12}$-ac-MeOH. https://doi.org/10.1103/physrevb.82.174405

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