EPR ofFe3+in aLaCaAlO4single crystal: Effect o

Abstract

EPR studies have been carried out on a Fe 3ϩ -doped LaCaAlO 4 single crystal at the X band ͑9.6 GHz͒ at room, liquid-nitrogen, and liquid-helium temperatures to study the effect of substitutional disorder that results when Ca 2ϩ and La 3ϩ ions substitute at the same site in this crystal. The variation of the observed Fe 3ϩ EPR linewidth as a function of the orientation of the external magnetic field with respect to the crystallographic c axis is found to be consistent with that reported previously for the Fe 3ϩ ion in YCaAlO 4 single crystal. This provides a confirmation of the disorder model proposed in oxide single crystals to explain the angular dependency of the linewidth behavior caused by statistical distribution of R 3ϩ ͑R denotes rare-earth ion͒ and Ca 2ϩ ions, situated in the same crystallographic position. The details of the manifestation of disorder in LaCaAlO 4 on EPR spectra have been provided. In addition, the EPR line positions have been exploited to estimate the Fe 3ϩ spin-Hamiltonian parameters in LaCaAlO 4 at 295, 77, and 4.2 K. The superposition model has been applied to calculate the Fe 3ϩ zero-field splitting parameter b 2 0 in RCaAlO 4 (RϭY, La) isostructural crystals, leading to the value of the intrinsic parameter b 2 (R 0 )ϭϪ119Ϯ1 GHz for R 0 ϭ1.784 Å. The liquid-helium temperature spectrum has been used to determine the absolute sign of the b 2 0 parameter, which is negative.

An X- and Q-band Gd3+ EPR study of a single crystal of EuAlO3: EPR linewidth variation with temperature and low-symmetry effects

“…In addition, EPR studies on the Cr 3+ ion in EuAlO 3 have been reported [8], as well as those on Gd 3+ in the isostructural LaAlO 3 and YAlO 3 crystals [9,10]. A relevant detailed EPR study of the Gd 3+ ion in monoclinic La 2 Si 2 O 7 and LaNbO 4 crystals, which are also characterized by a low (C S , and C 2 , correspondindly) point symmetry of the Gd 3+ ion and exhibit low-symmetry effects, was reported by Misra and Andronenko [11,12].…”

“…Alternatively, for Gd 3+ in La 2 Si 2 O 7 [11], the C S -axis is parallel to the X-axis, so that only those m n b , where m ( n) are odd and negative and n are 2, 4, 6, are non-zero. This is also the case for Gd 3+ in LaNbO 4 and PrNbO 4 [12]. The third 6 case, where C S is parallel to the Z-axis, occurs for Gd 3+ in YAlO 3 [6], where only those m n b , where m ( n) are even and negative and n are 2, 4, 6, describe the low-symmetry.…”

“…There is observed an increase in the EPR linewidth with increasing temperature. This is accounted for in the same way as that for the Van-Vleck paramagnet crystal PrNbO 4 [12]. Specifically, it is due to the dynamical exchange and dipolar interactions between Gd 3+ and the host paramagnetic Eu 3+ ions, which cause a significant temperature dependence of the linewidth, described as follows.…”