Stimulated scattering of electromagnetic radiation in thermodynamic-nonequilibrium media

Abstract

In the orthorhombic compound holmium trifluoride, HoF,, the trivalent holmium ion has a singlet ground state, with another singlet at 5.90 cm-l. Optical spectroscopy, magnetic and thermal measurements are used to investigate the behaviour of single crystals at 4.2 K and below. The results largely confirm the crystal-field analysis of Ram and Sharma, but give a value of 6.59 cm-' for the separation of the two singlets. It is found also that the system orders antiferromagnetically at TN = 0.53 K, with the holmium moments aligned parallel to the a axis. The enhancement of the I6'H0 NMR frequency is determined by a resonance experiment at 3.5 GHz. A simple theory of two electronic levels including hyperfine structure is used to interpret the results. Despite exceptionally large corrections required for the internal field, the magnetic and thermal measurements can be fitted using molecularfield theory.