Role of Magnetic Exchange Interactions in the Magnetization Relaxation of {3d–4f} Single‐Molecule Magnets: A Theoretical Perspective |
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Authors: | Dr Saurabh Kumar Singh Mohammad Faizan Beg Prof?Dr Gopalan Rajaraman |
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Institution: | Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 (India) |
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Abstract: | Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni3IIILnIII} star‐type complexes Ln=Gd ( 1 ), Dy ( 2 )] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow magnetization relaxation in complex 2 . DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1 . Acute ?Ni?O?Gd bond angles present in 1 instigate a significant interaction between the 4fxyz orbital of the GdIII ion and 3d orbital of the NiII ions, leading to rare and strong antiferromagnetic Ni???Gd interactions. Calculations reveal the presence of a strong next‐nearest‐neighbour Ni???Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI‐SO calculations performed on complex 2 suggest that the octahedral environment around the DyIII ion is neither strong enough to stabilize the mJ |±15/2〉 as the ground state nor able to achieve a large ground‐state–first‐excited‐state gap. The ground‐state Kramers doublet for the DyIII ion is found to be the mJ |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of magnetization (QTM). Using the POLY_ANISO program, we have extracted the JNiDy interaction as ?1.45 cm?1. The strong Ni???Dy and next‐nearest‐neighbour Ni???Ni interactions are found to quench the QTM to a certain extent, resulting in zero‐field SMM behavior for complex 2 . The absence of any ac signals at zero field for the structurally similar Dy(AlMe4)3] highlights the importance of both the Ni???Dy and the Ni???Ni interactions in the magnetization relaxation of complex 2 . To the best of our knowledge, this is the first time that the roles of both the Ni???Dy and Ni???Ni interactions in magnetization relaxation of a {3d–4f} molecular magnet have been established. |
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Keywords: | {3d– 4f} SMMs ab initio calculations CASSCF calculations density functional calculations magnetic properties {Ni3‐Ln} complexes {Ni‐Ln} SMMs |
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