QUANTUM OSCILLATIONS IN THE TRANSVERSE MAGNETORESISTANCE (SHUBNIKOV - DE HAAS EFFECT) AND ELECTRONIC CONDUCTION IN THE DILUTED MAGNETIC SEMICONDUCTOR MERCURY(1-X)IRON(X)SELENIDE
Abstract
A study of the quantum oscillations in the transverse magneto- resistance (Shubnikov-de Haas effect) in oriented single crystals of Hg(,1-x)Fe(,x)Se with x (LESSTHEQ) 0.06 has been made as a function of tempera- ture (1.3 K (LESSTHEQ) T (LESSTHEQ) 35K) and for magnetic fields less than 5 Tesla. Significant(, )differences in the temperature dependence of the amp- litude of the oscillations for magnetic fields oriented along 110 , 111 , and 001 have been observed. The analysis of the data for (')H// 110 provide evidence for spin dependent scattering of the conduction electrons. Lineshape fits to the data allow estimates for the difference Dingle temperature (delta)T(,D) and the exchange enhanced effective g-factor as a function of temperature and magnetic field. It is concluded that some Fe ions, when incorporated in a HgSe host, exist in a magnetically active state. This result indicates the presence of Fe('+3) in addition to the Fe('+2) that might normally be expected in this material. In addition the amplitude of these oscillations as a function of the magnet angle for two different planes of rotation for x = 0.03 and x = 0.05 have been measured. The results clearly show two sets of zeros in the amplitude of the fundamental harmonic with completely different angular dependences. Low field zeros (H < 1 Tesla) have been identified that have a similar angular dependence as those reported for HgSe. The position of the zeros can not be explained by the combination of two different signals which result from lack of the inversion symmetry in the zinc-blende structure of the lattice. A distinct set of high field zeros (H > 1 Tesla) have also been observed which exhibit a different angular dependence than the zeros formed in HgSe. Finally, the variation in the carrier concentration as function of annealing conditions in HgSe, Hg(,1-x)Mn(,x)Se, and Hg(,1-x)Fe(,x)Se has been studied. Our results show that the carrier concentration in Hg(,1-x)Fe(,x)Se system with x (GREATERTHEQ) .003 is very stable and shows no change under various annealing conditions. Measurements of the Dingle temperature from Shubnikov-de Haas oscillations, in addition to Hall mobilities at T = 4.2K, indicate a significantly longer collision time for the conduction electrons in Hg(,1-x)Fe(,x)Se for x (LESSTHEQ) 0.003 than in samples of HgSe with the same electron concentrations. The results of electron microprobe measurements on samples of Hg(,1-x)Mn(,x)Se and Hg(,1-x)Fe(,x)Se also suggest different temperature-composition diagrams for these two systems.
Degree
Ph.D.
Subject Area
Condensation
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