Electron paramagnetic resonance of Cr2+ and Cr4+ ions in CdGeAs2 crystals

Abstract

Electron paramagnetic resonance (EPR) has been used to investigate chromium ions in single crystals of CdGeAs2 grown by the horizontal gradient freeze technique. Signals from Cr2+ and Cr4+ ions were observed near 12 K. The Cr2+ ions have the 3d4 configuration with S=2 and substitute at the cadmium sites, while the Cr4+ ions have the 3d2 configuration with S=1 and substitute at the germanium sites. As a result, each impurity represents a neutral center. Both EPR spectra display the tetragonal symmetry of the lattice, which suggests that the centers most likely are not perturbed by nearby defects. The ratio of Cr2+ ions to Cr4+ ions in a particular CdGeAs2 crystal depends on the growth conditions and stoichiometry.

Paramagnetic Hexacyanometalates. The Diversity of Spin Distribution Studied by 13C and 15N MAS NMR Spectroscopy

“…Quite strikingly, [Cr(CN) 6 ] 4– does give 13 C NMR signals, whereas [Cr(CN) 6 ] 3– does not. This is useful for detecting low-spin Cr 2+ ions in the presence of Cr 3+ ions, and it is in accord with the electron relaxation time of Cr 2+ ions being shorter than that of Cr 3+ ions. , However, the spin state also plays an important role; for instance, high-spin Cr 2+ ions in octahedral and tetrahedral environments relax more slowly so that they can be detected by EPR methods …”

Improving optical transparency in CdGeAs2 crystals by controlling crystalline defects

“…Cr-related EPR signal intensity versus optical absorption at 5.5 mm (provided by N. Giles, West Virginia University). An increased incorporation of Cr 2+ , as monitored using EPR [25], was accompanied by improved optical transparency. boundary between the pitted and unpitted regions can be observed in Fig.…”

“…In another doping-absorption study, Garces et al [25] looked at Cr in CGA. Since Cr makes GaAs semiinsulating, this might be helpful in CGA by adding deep neutral centers to raise the Fermi level.…”

Enhanced magnetization in proton irradiated Mn3Si2Te6 van der Waals crystals

“…Alternatively, due to its large zero-field splitting (D = -2.48 cm -1 ) 56 , it could not be detected at X-band (9.43 GHz) frequency employed in the present work, often higher frequencies (>20 GHz) need to be employed. The presence of Cr 4+ (S = 1) 57 is ruled out from the absence of doublet with the separation about 1900 G. The increase in magnetization is too large to be explained solely by the adsorption of protons implanted. In that context, regarding the origin of enhanced magnetization, among others, the modification in the spin-lattice coupling and introduction of disorder appear to be the most general one.…”