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Structural Design of Easy‐Axis Magnetic Anisotropy and Determination of Anisotropic Parameters of Ln III Cu II Single‐Molecule Magnets
Author(s) -
Kajiwara Takashi,
Nakano Motohiro,
Takahashi Kohei,
Takaishi Shinya,
Yamashita Masahiro
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002434
Subject(s) - anisotropy , isostructural , magnetic anisotropy , chemistry , atmospheric temperature range , crystallography , ligand (biochemistry) , phase (matter) , condensed matter physics , magnet , field (mathematics) , relaxation (psychology) , magnetic field , nuclear magnetic resonance , materials science , magnetization , crystal structure , physics , thermodynamics , quantum mechanics , psychology , social psychology , biochemistry , receptor , organic chemistry , mathematics , pure mathematics
Four dinuclear Ln III Cu II complexes with Ln=Tb ( 1 ), Dy ( 2 ), Ho ( 3 ), and Er ( 4 ) were synthesized to investigate the relationship between their respective magnetic anisotropies and ligand‐field geometries. These complexes were crystallographically isostructural, and a uni‐axial ligand field was achieved by using three phenoxo oxygen groups. Complexes 1 and 2 displayed typical single‐molecule magnet (SMM) behaviors, of which the out‐of‐phase susceptibilities were observed in the temperature range of 1.8–5.0 K ( 1 ) and 1.8–20.0 K ( 2 ). The Cole–Cole plots exhibited a semicircular shape with α parameters in the range of 0.08–0.18 (2.6–4.0 K) and 0.07–0.24 (3.5–7.0 K). The energy barriers Δ/ k B were estimated from the Arrhenius plots to be 32.9(4) K for 1 and 26.0(5) K for 2 . Complex 3 displayed a slow magnetic relaxation below 3.0 K, whereas complex 4 did not show any frequency‐dependent behavior for both in‐phase and out‐of‐phase susceptibilities, which indicates that easy‐axis anisotropy was absent. The temperature dependence of the dc susceptibilities for the field‐aligned samples of 1 – 3 revealed that the χ M T value continuously increased as the temperature was lowered, which indicates the presence of low‐lying Stark sublevels with the highest | J z | values. In contrast, complex 4 displayed a smaller and temperature‐independent χ M T value, which also indicates that easy‐axis anisotropy was absent. Simultaneous analyses were carried out for 1 – 3 to determine the magnetic anisotropy parameters on the basis of the Hamiltonian that considers B 2 0 , B 4 0 , and B 6 0 .