Spin state and exchange in the quasi-one-dimensional antiferromagnet KFeS2 |
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Authors: | Satish Kumar Tiwary Sukumaran Vasudevan |
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Institution: | (1) Department of Inorganic and Physical Chemistry, Indian Institute of Science, 560012 Bangalore, India |
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Abstract: | We report the optical spectra and single crystal magnetic susceptibility of the one-dimensional antiferromagnet KFeS2. Measurements have been carried out to ascertain the spin state of Fe3+ and the nature of the magnetic interactions in this compound. The optical spectra and magnetic susceptibility could be consistently
interpreted using aS=1/2 spin ground state for the Fe3+ ion. The features in the optical spectra have been assigned to transitions within thed-electron manifold of the Fe3+ ion, and analysed in the strong field limit of the ligand field theory. The high temperature isotropic magnetic susceptibility
is typical of a low-dimensional system and exhibits a broad maximum at ∼565K. The susceptibility shows a well defined transition
to a three dimensionally ordered antiferromagnetic state atT
N=250 K. The intra and interchain exchange constants,J andJ′, have been evaluated from the experimental susceptibilities using the relationship between these quantities, andχ
max,T
max, andT
N for a spin 1/2 one-dimensional chain. The values areJ=−440.71 K, andJ′=53.94 K. Using these values ofJ andJ′, the susceptibility of a spin 1/2 Heisenberg chain was calculated. A non-interacting spin wave model was used belowT
N. The susceptibility in the paramagnetic region was calculated from the theoretical curves for an infiniteS=1/2 chain. The calculated susceptibility compares well with the experimental data of KFeS2. Further support for a one-dimensional spin 1/2 model comes from the fact that the calculated perpendicular susceptibility
at 0K (2.75×10−4 emu/mol) evaluated considering the zero point reduction in magnetization from spin wave theory is close to the projected
value (2.7×10−4 emu/mol) obtained from the experimental data. |
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Keywords: | Low-dimensional materials magnetic ordering and exchange spin-waves |
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