A. A. Samokhvalov

Red Shift of Absorption Edge and Nonmetal–Metal Transition in Single Crystals La1—xSrxMnO3 (x = 0.1, 0.2, 0.3)

The red shift of the fundamental absorption edge (mo.16 eV) of a La 0.9 Sr 0.1 MnO 3 single crystal occurs as the crystal is cooled into the ferromagnetic phase. This result shows that there exist spin-dependent states. The reflection and absorption spectra of La 1-x Sr x MnO 3 single crystals (x = 0.1, 0.2, 0.3) indicate that the red shift may be the reason for the appearance of free charge carriers participating in the colossal magnetoresistance phenomenon. The nonmetal-metal type transition below T C confirms this.

Optical-absorption anomalies near magnetic phase transitions in copper oxide

AbstractThe optical absorption coefficient in the region of a wide charge-transfer band in copper oxide CuO (ℏω=3.19 eV) exhibits sharp and anomalously large (up to 8% (!)) changes near two magnetic phase transition temperatures

Effect of electron bombardment on a phase-inhomogeneous nanoscopic structure and the fundamental absorption spectrum of single-crystal CuO

(T_{N_1 } \approx 213 K and T_{N_2 } \approx 230 K)

Low-mobility charge carriers in CuO

. It is shown that the wide fundamental absorption bands can be used for optical detection of magnetic phase transitions, the parameters of long-and short-range magnetic order, and the effects of a magnetic-impurity state.

Absorption spectra of CuO single crystals near the absorption edge and the nature of the optical gap in copper oxides

Irradiation of various single-crystal CuO faces [ac,bc,(110)] with 4.6-MeV He+ ions has been found to result in reduction of CuO to Cu2O and Cu on the irradiated and unirradiated sides, lifting of forbiddenness from optical transitions in the [CuO4]7− electron center in the 0.7–0.95-eV energy range, a change in dichroism near the bands corresponding to transitions in the hole centers, [CuO4]5−, and electron centers, [CuO4]7−, as well as in a resonant increase of absorption at 0.95–1.30 eV with an unusual polarization dependence. The results of He+ irradiation of CuO single crystals are discussed in terms of a model of the nucleation of the phase of polar (electron and hole) centers in copper-oxygen systems.

The CuO single crystal: anomalies in the thermal expansion and the magnetostriction

The optical absorption spectra of single-crystal CuO bombarded with 5-MeV electrons exhibit reduced absorption in the region of the fundamental absorption edge at 17 eV, which corresponds to the b1g→eu transition with charge transfer in CuO46−. A simultaneous increase in absorption is observed in the middle infrared and in the region of high energies centered on 2.9 eV. The experimental results obtained are interpreted in terms of ideas on the phase-inhomogeneous nano-agglomorated structure in copper oxides that occurs as a result of the nucleation of polar centers (CuO45−, CuO47−) under electron bombardment.