Localized magnon gap modes in the 2-d Ising antiferromagnets K2CoF4 and Rb2CoF4 |
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Authors: | E Betz W Knierim U Dürr |
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Institution: | Physikalisches Institut der Universität Stuttgart, Teil II, 7000 Stuttgart 80, Fed. Rep. Germany |
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Abstract: | The defect (Mn2+,Ni2+,Fe2+) induced magnon gap modes in the layered antiferromagnets K2CoF4 and Rb2CoF4 were investigated with the methods of FIR absorption-and IR emission spectroscopy. The anisotropic exchange-parameters describing the strongly localized Mn2+ spin excitations far below the host lattice magnon band and the Ni2+ excitations in the vacinity of this band are presented. In the diluted system K2Co1-cMncF4 localized Mn2+ cluster modes up to about C≈0.1 were observed. The excitation energy of these modes can only be explained by assuming an anisotropic Mn2+-Mn2+ exchange which is in contrast to the pure isomorphous system K2MnF4. In the spin mismatch system K2CoF4: Fe the magnetic moments of the isolated Fe2+ impurities are pulled from the plane perpendicular to the c-axis and aligned parallel to the easy axis of the magnetic crystal. |
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