Knowledge Bank

Using interferometric far infrared spectroscopic techniques, the zero magnetic field anti-ferromagnetic resonance in seven compounds of the face centered type $(M2ReX6)$ containing $ReCl=6$ and $ReBr=6$ have been observed at $1.5\circ K$. Re-Re pair spectra in typical diamagnetic host crystals such as $K2PtCl6$ have been observed allowing a determination of the isotropic and anisotropic exchange parameters. The antiferromagnetic resonance has been interpreted in terms of a magnetic type 3 ordering. Since little or no lattice distortion occurs in these compounds upon antiferro-magnetic ordering, the compounds of this system offer an example of exchange parameter determination as a function of lattice parameter as well as cation exchange effects. Examples of phonon-spin wave coupling have been observed in the far infrared spectra. Diamagnetic isomorphic crystals were used to locate vibronic and lattice modes.