High-magnetic-field EPR of Cr-based diluted magnetic semiconductors

Abstract

We have studied magnetic interactions in chromium-based diluted magnetic semiconductors by measuring in detail the electron paramagnetic resonance spectrum of Cr 2ϩ over the frequency range between 30 and 210 GHz at high magnetic fields up to 20 T oriented along different crystal axes. At low temperatures, crystals of chromium-alloyed zinc chalcogenides Zn 1Ϫx Cr x ͑S, Se, Te͒ demonstrate complex properties that are neither of Brillouin nor of Van Vleck type. The behavior of these Cr 2ϩ impurities in semimagnetic materials results from the interaction of the ground state with the low-lying electronic states of the 3d Cr 2ϩ ion and from the Jahn-Teller-induced distortion of the Cr 2ϩ position in the host lattice. We measured optical transitions between these states and we could determine the magnetic-field dependence and the anisotropy of the electronic levels. We explain our results with the crystal-field model proposed by Vallin et al., 1 including a cubic crystal field and Jahn-Teller distortion, and we evaluate the dependence of the model parameters on the semiconductor host lattice.

EPR Spectra of Cr in CdTe Crystals

“…The observed ferromagnetic p−d exchange interactions in zinc chalcogenides recommends them as the material for spintronics as well [2,6,7]. EPR investigations of the chromium in these crystals reveals this dopant in Cr 2+ state [8,9]. In CdTe matrix the chromium was detected in the same state Cr 2+ [8].…”

Chromium-Doped ZnO Nanoparticles Synthesized by Co-Precipitation: Chromium Effects

“…However, our g-value and the peak-to-peak line width are in contradiction with the reported values of the ESR spectra of Cr 2+ in II-VI compounds. Vallin et al [40] showed that the Cr 2+ ESR spectra in II-VI compounds have peak-to-peak line widths of 500 G at 20 K. Therefore, the expectation is that at room temperature, ESR signal of Cr 2+ will be broader and unable to observed [41]. Additionally, a study of Cr doped GaAs [42] revealed that the Cr 3+ valence state is predominant if the chromium concentration significantly exceeds the concentration of shallow donors in the crystal.…”

Парамагнитные дефекты в кристаллах ZnSe, активированных ионами железа

“…Хотя тригональный центр обнаружен не был, регистрировались резонансные переходы типа 0 ↔ ±1 иона Cr 2+ . ЭПР-спектроскопия иона Cr 2+ (d 4 , 5 D, S = 2) в ZnSe хорошо изучена [10][11][12], и идентификация этой примеси не представляет сложности. Во-первых, угловая зависимость обнаруженных переходов (в ста-тье не показана) свидетельствовала о тетрагональной симметрии центров, что соответствует литературным данным.…”