We report measurements of the susceptibility in the temperature range from 3.5 to 6.0 K of a series of Mn12 -ac and Mn12 -ac-MeOH samples in the shape of rectangular prisms of length lc and square cross section of side la. The susceptibility obeys a Curie-Weiss law, χ=C/ (T-θ), where θ varies systematically with sample aspect ratio. Using published demagnetization factors, we obtain θ for an infinitely long sample corresponding to intrinsic ordering temperatures T c ≈0.85K and ≈0.74 K for Mn12 -ac and Mn 12 -ac-MeOH, respectively. The difference in Tc for two materials that have nearly identical unit cell volumes and lattice constant ratios suggests that, in addition to dipolar interactions, there is a nondipolar (exchange) contribution to the Weiss temperature that differs in the two materials because of the difference in ligand molecules.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 3 Nov 2010|