Magneto-structural correlation in the Jahn–Teller isomers of Mn12

Abstract

In this Feature Article, we discuss our work on the Jahn–Teller isomers in a single molecule magnet, [Mn₁₂O₁₂(RCO₂)₁₆(H₂O)₄] (abbreviated as Mn12R), and the magneto-structural correlation between them. Mn12R derivatives always exhibit two peaks at 5 and 2 K in the temperature dependence of the imaginary component of the ac susceptibility χ″, suggesting the presence of a slower relaxation (SR) process and a faster relaxation (FR) process. Although the peak at 2 K used to be regarded as an impurity effect due to its weakness, recent studies have revealed that it is caused by a Jahn–Teller isomer. Most of the Mn12R crystals are now recognized as mixed crystals of SR and FR molecules having a structural difference in the Jahn–Teller distortion at Mn³⁺. In the SR molecule, the elongated Jahn–Teller axes of Mn³⁺ ions are all nearly parallel to the molecular axis of Mn12R, while the FR molecule includes an Mn³⁺ site of unusual Jahn–Teller distortion. The angular-dependent magnetic measurements on Mn12Ph indicated that the magnetic easy axis of the FR species was tilted by 12° from the pseudo-D_4h molecular axis, while that of the SR molecule was parallel to it. High pressure was found to bring about a transformation of the SR species into FR even in Mn12Me, in which the number of FR species was negligible at ambient pressure. The structural and magnetic studies on a nearly 1 ∶ 1 mixed crystal of Mn11CrMe and Mn12Me indicated that the magnetic anisotropy of Mn11CrMe was nearly identical to that of Mn12Me, though Mn11CrMe included a non-Jahn–Teller ion Cr³⁺ in the molecular skeleton of Mn12.