Slow Magnetic Relaxation of Linear Trinuclear M(II)–Gd(III)–M(II) Complexes with D3 Point Group Symmetry (M(II) = Zn(II) and Mg(II))

Abstract

Trinuclear M(II)-Gd(III)-M(II) complexes 1 (M = Zn), 2 (M = Mg), and the magnetically dilute sample 1′ were synthesized and the slow magnetization relaxation originating from Gd(III) ions was investigated in detail. These complexes are crystallographically isostructural and belong to D3 point group symmetry, with M-Gd-M arrayed on the crystallographic 3-fold axis. From the angular-resolved magnetization of a single crystal of 1, an easy-axis-type magnetic anisotropy of Gd(III) with an anisotropy parameter D of −0.21(3) K were revealed. All the complexes underwent slow relaxation under the application of an external magnetic field. The temperature dependence of the relaxation rate τ–1 differed considerably between 1′ and 1, 2 such that: for 1′,τ–1∝ T1.1 over the entire temperature range, whereas for 1 and 2, τ–1 ∝ T1.56 and τ–1 ∝ T1.49 above 3 K, respectively. The discrepancy can be attributed to the presence of competing multiple relaxation processes, such as direct and Raman processes, and at dilution, the direct process becomes faster, leading to its predominance in 1′. For 1 and 2, the larger power number (∼1.5) was attributed to the significantly greater contribution from the Raman process, which may be originated from intramolecular atomic vibrations.