Electronic structure and magnetic anisotropy for nickel-based molecular magnets

Recent magnetic measurements on molecular magnets [Ni(hmp)(ROH)Cl](4), where R=CH3, CH2CH3, or (CH2)(2)C(CH3)(3), and limp is the monoanion of 2-hydroxymethylpyridine, revealed a strong exchange bias prior to the external magnetic-field reversal as well as anomalies in electron paramagnetic-resonance peaks at low temperatures. To understand the exchange bias and observed anomalies, we calculate the electronic structure and magnetic properties for the Ni-4 molecules with the three different ligands, employing density-functional theory. Considering the optimized structure with possible collinear spin configurations, we find that the lowest-energy state has a total spin of S=0. The magnetic anisotropy barrier to reverse the magnetic moments of all four Ni ions simultaneously is calculated to be 4-6 K. (c) 2005 American Institute of Physics.