Multi‐Path Magnetic Relaxation of Mono‐Dysprosium(III) Single‐Molecule Magnet with Extremely High Barrier

Abstract

Lanthanide complexes have attracted considerable attention because of their electronic properties such as magnetism [1][2][3][4] and luminescence. [5] In the research area of molecule-based magnets, single-molecule magnets (SMMs), that are formed through the combination of a large spin multiplicity of the ground state and an easy-axis (or Ising-type) magnetic anisotropy of the entire molecule, have been extensively investigated. Heavy lanthanide ions are being used for designing SMMs because of their large angular momentum in the ground multiplet state and large magnetic anisotropy. In a previous study, [6] our research group has demonstrated a technique for designing the magnetic anisotropy of heavy lanthanideA C H T U N G T R E N N U N G (III) ions by controlling the ligand field (LF) anisotropy in a series of isostructural Ln III -Cu II complexes (Ln = Tb, Dy, Ho, and Er) as well as in a wheel shaped Er III -Zn II 3 complex. Although the inner 4f electrons are effectively shielded by the 5s and 5p electrons, the 4f electrons are, nonetheless, affected by the negative charges of donor atoms that form an anisotropic electrostatic field. This allows for flexibility in the control of magnetic anisotropy by designing the LF. For example, the Dy III ion with a f 9 configuration has an 6 H 15/2 ground state of j J, J z > = j 15/2, J z > (J z = AE 15/2, AE 13/2, .., AE 1/2), and the sub-levels with the largest j J z j value, j 15/2, AE 15/2 > , are known to have an oblate spheroidal electronic distribution.[7] The stabilization of these two sub-levels leads to stronger easy-axis anisotropy, which was achieved by locating strong negative charges at axial positions. The theoretical analysis of the Dy III -Cu II complex in the previous work predicted an extremely large LF splitting of the Stark sub-levels (> 400 K), which engages a very strong SMM feature of this complex; however, the observed barrier for magnetization reversal was approximately 32 K.[6a] Because of the exchange interaction with Cu II , the ground sub-level of Dy III is further split into two levels with a separation of 26 K, which may be related to the observed barrier. We theorized that the absence of Cu II would enhance the high potential of the Dy III ion for the construction of SMMs, and by changing Cu II to diamagnetic Zn II , we achieved a single-ion SMM with a huge magnetic anisotropy that is close to the theoretical value. Herein, we report the synthesis, structure, and detailed SMM behavior of a Dy III -Zn II dinuclear complex (1, Figure 1) in which the Dy III ion is the only paramagnetic center.Compound 1 was obtained by reacting dysprosiumA C H T U N G T R E N N U N G (III) nitrate, salicylaldehyde (Hsal), and bromide ion with the mono-zinc(II) complex [Zn(L)] (H 2 L denotes a Schiff-base ligand formed by a condensation reaction of o-vaniline and 2,2-dimethylpropanediamine in a 2:1 ratio) [8] in the presence of a base. X-ray analysis (Figure 1) Figure 1. An ORTEP drawing of complex 1 with selected atom numbering (50 % probability ellipsoids)...

The role of anharmonic phonons in under-barrier spin relaxation of single molecule magnets

“…For instance, the low- T relaxation time of Dy 3+ is defined by a double-exponent Arrhenius curve with the two fitted effective barriers (334 and 94 K) being lower than the first accessible spin exited state (430 K)30. This behaviour suggests the existence of two different spin relaxation mechanisms which, in light of our discussion, could be attributed to the effect of different normal modes.…”

Phenalenyl-based mononuclear dysprosium complexes

“…At a frequency of 1500 Hz, the out-of-phase component first reaches a maximum at 13 K and then steadily increases rather than declining to zero while decreasing the temperature. This indicates a transition from a thermally activated to a temperature-independent regime in the relaxation process [36,50–51]. Shape and frequency dependence of the out-of-phase component in ac susceptibilities suggests that 1 might be a SMM.…”

A Basis for Lanthanide Single-Molecule Magnets

“…Further studies for redox, heteroleptic, and multidecker species of this class of complexes [53][54][55][56][57] were performed and thus created a high effective barrier record of SMM field, U eff = 652 cm −1 (938 K) [56], which surpasses by an order of magnitude that obtained for the original Mn 12 SMM. Remarkably, the interest in new kinds of mononuclear lanthanide SMMs [58] is continuing in recent years, and some of them show the very high effective barrier and blocking temperature, such as β-diketone [59][60][61][62], organometallic [35,37,44,63], 2013 [74] and some low-symmetry [20,64] lanthanide systems (Table 1.4). As such, the mononuclear SMMs are called single-ion magnets (SIMs) in some recent papers.…”