Exchange bias in Ni 4 single-molecule magnets

Electronic structure and magnetic anisotropy for nickel-based molecular magnets

“…For Ni 4 , the tunneling was observed prior to magnetic field reversal but no tunneling in zero magnetic field. 4 The similar behavior has been observed in a dimeric form of the molecular…”

“…However, more scrutinized studies are required to conclude that this, in fact, attributes to the antiferromagnetic coupling in the calculated lowest-energy state. Another intriguing point is that as shown in Table I, collinear spin excitations for Ni 4 have an order of magnitude lower energies than those for the Mn 12 -acetate 14 and Mn 4 monomer 15,16 . A majorityminority spin-flip gap ranges from 1.4 eV to 1.6 eV and a minority-majority spin-flip gap varies between 1.8 eV and 2.1 eV depending on ligands as shown in Table III.…”

“…The first prototype molecular magnet is Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 (hereafter Mn 12 -acetate), 1 which has a total ground-state spin of S = 10 and magnetic anisotropy barrier of 65 K. 2,3 Magnetic hysteresis loop measurements on Mn 12 -acetate showed quantum tunneling of magnetic moment through the magnetic anisotropy barrier when the external magnetic field was applied along the easy axis. 3 Recently molecular magnets [Ni(hmp)(ROH)Cl] 4 (hereafter Ni 4 ) were synthesized, 4 where R=CH 3 , CH 2 CH 3 , or (CH 2 ) 2 C(CH 3 ) 3 (abbreviated to Me, Et, and tBuEt, respectively). They revealed qualitatively different tunneling features from the typical molecular magnets such as Mn 12 -acetate.…”

“…Unlike Mn 12 -acetate and Mn 4 dimer, the Ni 4 molecular magnets are not well separated from each other so that there are four interacting nearest neighboring molecules. 4 The intermolecular interactions can be tailored by different sizes of ligands such as MeOH, EtOH, and tBuEtOH. Among the three different types of Ni 4 , the MeOH and EtOH complexes consist of two sublattices, each of which is an inter-penetrating diamond lattice.…”

Landau-Zener tunneling in the presence of weak intermolecular interactions in a crystal ofMn4single-molecule magnets

“…Until recently, such intermolecular exchange interactions have been assumed to be negligibly small. However, our recent studies on several SMMs suggest that in most SMMs exchange interactions lead to a significant influence on the tunnel process 19,20,21,22,23 . The main difference between dipolar and exchange interactions are: (i) dipolar interactions are long range whereas exchange interactions are usually short range;…”