Low Frequency Excitations in Antiferromagnetic Tungstates (NiWO/sub 4/, CoWO/sub 4/)

Synchrotron-based far-infrared spectroscopy of nickel tungstate

“…3 that confirms the absence of any structural phase transition in NiWO 4 and CoWO 4 at atmospheric pressure from 5 to 300 K. Finally, we did not observe in our polycrystalline NiWO 4 sample any absorption related to magnetic excitations at 119 cm −1 , which was found previously in [24]. Also no AFMR modes, observed in [24] at 67 and 79.3 cm -1 , were found in IRspectra of CoWO 4 .…”

“…: a value close to the doubled exchange energy [24]. It was found in [25] for cobalt (CoF 2 , CoWO 4 ) and manganese (MnCO 3 , MnF 2 , RbMnF 3 , KMnF 3 ) containing compounds that the maximum frequency in the spin-wave spectrum, estimated from the AFMR follows a linear dependence on the Néel temperature.…”

“…It was found in [25] for cobalt (CoF 2 , CoWO 4 ) and manganese (MnCO 3 , MnF 2 , RbMnF 3 , KMnF 3 ) containing compounds that the maximum frequency in the spin-wave spectrum, estimated from the AFMR follows a linear dependence on the Néel temperature. Applying the same procedure to nickel compounds (NiF 2 , KNiF 3 , NiO), one can estimate a value for NiWO 4 close to 108 cm −1 , and thus the value of the doubled exchange energy ~216 cm −1 , which is nearly two times larger than proposed from AFMR measurements in [24].…”

“…A comparison with isostructural non-magnetic ZnWO 4 and antiferromagnetic CoWO 4 (T N = 55 K) compounds and first-principles linear combination of atomic orbital (LCAO) calculations was used to assign unambiguously the phonon bands with the aim to find possible magnetic excitations [24] and their temperature dependence in antiferromagnetic NiWO 4 phase.…”