Giant coercivity and high magnetic blocking temperatures for N2 3− radical-bridged dilanthanide complexes upon ligand dissociation

Abstract

Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (CpMe4H) capping ligands with strong magnetic exchange coupling provided by an N2 3− radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20 K, as observed for the complex [K(crypt-222)][(CpMe4H 2Tb)2(μ−)].

Cyclopentadienyl Ligands in Lanthanide Single-Molecule Magnets: One Ring To Rule Them All?

“…[9][10][11]13 Using the unusual S = ½ radical bridging ligand [N2] 3- 19 rate of 0.01 T s -1 ) (Figure 4). 40 Whilst the key temperatures for these radical-bridged SMMs are still firmly in the liquid-helium regime, it has been noted that their coercive fields far exceed those of commercial rare-earth magnets, further highlighting the potential of SMMs.…”

“…Rather, the preferred interpretation is to invoke a dominant role for lattice vibrations and detrimental relaxation arising from spin-phonon coupling via four C-H oscillations, as proposed in a separate study on 15. 40 However, whilst dysprosium metallocene cations remain represented by a sole example, it may be that a general explanation for the magnetic relaxation should wait until more data on closely related systems is available. More research is needed; in the meantime, the importance of structural factors such as the Cp-Dy-Cp bending angle and the steric properties of the ligand should not be overlooked.…”

Rare‐Earth Cyclobutadienyl Sandwich Complexes: Synthesis, Structure and Dynamic Magnetic Properties

“…Since the magnetic memory properties of SMMs have been used as a basis for proposing nanoscale devices, the magnetisation ( M ) vs. field ( H ) hysteresis properties of [K 2 (toluene) 2 Dy ] are also of interest. The M ( H ) data (Figure ) show hysteresis loops that remain open up to 7 K (scan rate of 50 Oe s −1 ), but without any appreciable coercivity.…”

Prediction of a Nine−Membered Aromatic Heterocyclic 1,4,7−triazacyclononatetraenyl anion and its Sandwich Complexes with Divalent Lanthanides

“…The sandwich shaped metallocenes complexes have been discovered more than six decades ago, however, they still continue to attract considerable attention from scientists because of their interesting structure, bonding as well as their various applications in designing materials for single−molecule magnet, spintronics and catalysis. [1−4] Besides, metallocenes play an important role in the development of new class of materials, associated with intriguing electronic and magnetic properties Recently a new surface−supported one−dimensional organometallic sandwich molecular nanowires associated with ferromagnetic insulator properties has been synthesized .…”