J. Pescia

Temperature and concentration dependences of the spin-lattice relaxation rate in four borate glasses doped with Fe2O3

Spin-lattice relaxation time (T1) of Fe3+ ions has been measured in four borate glasses doped with 0.25, 0.5, 1 and 3 wt.% Fe2O3 by the modulation method over the temperature range 5–250 K. In the three less concentrated samples, it was observed thatT1−1. αT at intermediate temperatures. This is explained in terms of a relaxation mechanism involving TLS (Two Level Systems). At higher temperatures, the temperature dependence ofT1−1 is slowed down by cross-relaxation. In the most concentrated sample, the exchange interaction plays a dominant role leading to a very different relaxation-time behaviour, described well by the Bloembergen and Wang three-reservoir model.

Electron spin-lattice relaxation of Yb3+ and Gd3+ ions in glasses

The electron spin-lattice relaxation rate (T1−1) was measured in two glass samples: (i) a phosphate glass doped with 1 wt% Yb2O3 and (ii) a Li2Si4O9 glass sample doped with 0.2 wt% Gd2O3. In the Yb3+-doped glass sample,T1 was measured by an electron-spin-echo technique from 4.2 to 6 K, by the modulation method from 10 to 26 K and by the EPR linewidth from 30 to 100 K. It was found thatT1−1 αTn withn=9 in the range 4.2–6 K.n decreased gradually as the temperature was increased and tended towards 2 above 40 K. Over the entire temperature range 4.2–100 K,T1−1 was fitted toAT+BT9J8 (ΘD/T) (whereA andB are two temperature-independent constants,J8 is the well-known Van Vleck integral andΘD is the Debye temperature). The value ofΘD (=46.3±0.9 K) so determined is in good agreement with that of Stevens and Stapleton from theirT1 measurements in the range 1.5 to 7 K. In the Gd3+-doped glass, it was observed thatT1−1 αT over the range 50–150 K. The data for Ye3+-doped glass sample were accounted for by assuming that the phonon modulation of the ligand field is the dominant mechanism, associated with a low Debye temperature in accordance with the published data obtained by using other techniques to study lattice dynamics. On the other hand, the data on the Gd3+-doped glass sample were explained to be predominantly due to a mechanism involving Two-Level-Systems (TLS)

An EPR study of dilute magnetic semiconductors Hg1−xCoxSe (x = 0.0045 and x = 0.0087)

Abstract X-band (≈9.3 GHz) EPR spectra are recorded from room temperature down to 5 K on two samples of symmetry-induced zero band gap semiconductor Hg 1− x Co x Se ( x = 0.0045 and 0.0087), previously subjected to electron bombardment. Both the samples exhibit, in addition to a narrow intense line ( g = 2.018) due to trapped electron/ defect centre, a broad Co 2+ EPR line (overlap of the transitions M s = ± 1 2 ↔ ± 3 2 ) characterized by g = 2.027, which disappears at low temperatures. In addition, only the EPR spectra of the sample with the larger concentration of Co ions reveal the presence of an extra EPR line with the value of g = 2.024 at temperatures below 40 K. (This line was, however, found to be present in another sample with the lower concentration.) This extra line is interpreted to be due to the Kramers doublet (M s = ± 1 2 ) of the Co 2+ ion. The present EPR data do not indicate the presence of Co 3+ ions.

Spin relaxation in TMMC: Evidence of two paramagnetic species

Abstract We have observed in monocrystals of TTMC an anomalous behaviour of the ESR line width, line shape and spin lattice relaxation, when the temperature is varied. These results are explained by the presence of 1 d and 3 d paramagnetic species. The relative concentration of these species has been estimated.

Spin-lattice relaxation in glasses doped with Fe2O3

Abstract We investigated the thermal dependence of the electron spin-lattice relaxation time T 1 by the modulation method over the 10 to 290 K temperature range in five silicate or barium vanadate glasses doped with Fe 2 O 3 . Our data are viewed with respect to the theory of Kurtz and Stapleton and are compared to results concerning the optical linewidth.