Magnetic measurements on quaternary manganese-based diluted magnetic semiconductors

Farida Mohiuddin, Purdue University

Abstract

We have studied the magnetic properties of Mn-based quaternary diluted magnetic semiconductors, Cd$\sb{1-x-y}$Zn$\sb{y}$Mn$\sb{x}$Te, Cd$\sb{1-x-y}$Mg$\sb{y}$Mn$\sb{x}$Te, Cd$\sb{1-x}$Mn$\sb{x}$Te$\sb{1-y}$Se$\sb{y}$ and Zn$\sb{1-x-y}$Mg$\sb{y}$Mn$\sb{x}$Te. The emphasis was on investigating the host dependence of the exchange interactions through the effective nearest neighbor exchange interaction, $J\sb1/k\sb{B}$, and the spin glass transition temperature, $T\sb{f}$, at fixed low Mn concentration, x = 0.10, and different relative concentrations of the host constituents. The $T\sb{f}$ was obtained from ac magnetic susceptibility measurements at 450 mK $<$ T $<$ 4 K and $J\sb1/k\sb{B}$ was obtained from a Curie-Weiss fit to the magnetization data measured at 4.5 K $<$ T $<$ 300 K for nominal x = 0.10 samples. From the study of the Cd$\sb{1-x-y}$Zn$\sb{y}$Mn$\sb{x}$Te series we showed that $T\sb{f}$ and $J\sb1/k\sb{B}$ varied linearly as a function of Zn concentration and the fractional change was 0.64 and 0.70 respectively, which within the error bars are identical. The observed host dependence of $T\sb{f}$ contradicts the universality in $T\sb{f}$ for wide-gap DMS systems that was suggested in earlier measurements. The Mg-based quaternary DMS are relatively new and they showed spin-glass transition at low temperatures. We did not observe any systematic variation of $T\sb{f}$ and $J\sb1/k\sb{B}$ in the Cd$\sb{1-x-y}$Mg$\sb{y}$Mn$\sb{x}$Te series at fixed x = 0.10 within our resolution. $T\sb{f}$ was also measured for 0.2 $<$ x $<$ 0.60 for this series. Assuming a power law decay of the exchange interactions we plotted $T\sb{f}$ vs. x on a log-log scale for three quaternary series. All the data points for the entire Mn concentration range could be represented by a single line for each of the three plots with the decay exponent, n = 6.36 $\pm$ 0.50, 6.69 $\pm$ 0.40 and 6.69 $\pm$ 0.70 for Cd$\sb{1-x-y}$Zn$\sb{y}$Mn$\sb{x}$Te, Cd$\sb{1-x-y}$Mg$\sb{y}$Mn$\sb{x}$Te and Cd$\sb{1-x}$Mn$\sb{x}$Te$\sb{1-y}$Se$\sb{y}$ respectively, which is consistent with the value 6.8 observed earlier for Mn-based wide-gap quaternary DMS.

Degree

Ph.D.

Advisors

Crooker, Purdue University.

Subject Area

Condensation|Materials science

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