MAGNETO-OPTICAL STUDIES OF DILUTED MAGNETIC SEMICONDUCTORS. I. INELASTIC LIGHT SCATTERING. II. FARADAY ROTATION
Abstract
We have investigated Raman scattering associated with the excitations of the Mn('2+) 3d electrons in diluted magnetic semi- conductors in an applied magnetic field. A sharp Raman line due to the spin-flip of the 3d electrons, corresponding to the (DELTA)m(,s) = (+OR-)1 transition, occurs in the paramagnetic phase and corresponds to a g-factor of 2. Close to band gap resonance, this transition in combination with the zone center LO phonons as well as the (DELTA)m(,s) = (+OR-)2 transitions are present. This resonance was explored with magnetic field and temperature tuned resonant Raman scattering involving the large magnetic field induced exciton splitting. The (DELTA)m(,s) = (+OR-)1 transition was also observed for Co('2+) ions in Cd(,1-x)Co(,x)Se and was found to have a g-factor of 2.32. A spin-flip Raman scattering study of electrons bound to shallow donors was carried out in the diluted magnetic semiconductors Cd(,1-x)Mn(,x)Te and Cd(,1-x)Mn(,x)Se for x(, )< 0.30 and in Cd(,1-x)Mn(,x)S for x = 0.022 and 0.125. This spin-flip Raman scattering was observed for the temperature range 1.8 K (LESSTHEQ) T (LESSTHEQ) 160 K and for magnetic fields (LESSTHEQ)60 kG. The large spin-flip energies result from the exchange coupling of the electron with the Mn('2+) ions. Finite Raman shifts are observed in the absence of a magnetic field and are attributed to the bound magnetic polaron and thermal fluctuations on the local magnetization. The temperature and magnetic field depend- ence of the spin-flip energies and polarizations are compared with a statistical-mechanical model, the agree is good for x(, )< 0.15. Spin-flip Raman scattering is also observed in Cd(,1-x)Co(,x)Se and Cd(,1-x)Fe(,x)Se. Raman scattering from antiferromagnetically coupled Mn('2+) pairs has been observed in Cd(,1-x)Mn(,x)S and in Cd(,1-x)Mn(,x)Se. A series of Raman peaks corresponding to (DELTA)S = (+OR-)1 are seen whose positions agree well with the expected energy scheme of Mn('2+) pairs. From these peaks we have a direct measurement of the Mn('2+) nearest neighbor exchange constant. The NN-pairs seen in Cd(,1-x)Mn(,x)S are resolved into doublets implying the existence of two nearest neighbor exchange constants. Weaker Raman peaks are seen in Cd(,1-x)Mn(,x)S corresponding to next nearest neighbor Mn('2+) pairs and NN-open-triangle triplets. Faraday rotation as a function of Mn('2+) concentration, temperature, and magnetic field is measured in the zincblende diluted magnetic semiconductors Zn(,1-x)Mn(,x)Te and Cd(,1-x)Mn(,x)Te. The effects of the large exchange coupling between the 3d electrons of the Mn('2+) and the band electrons are strikingly manifested in the interband Faraday effect leading to very large rotations. For large x, the effects of Mn-Mn antiferromagnetic exchange interaction are observed in the temperature dependence of the Faraday rotation.
Degree
Ph.D.
Subject Area
Condensation
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