We have studied the optical, magnetic, and magneto-optical properties of diluted magnetic semiconductor Cd1-x-yMnxTMyTe (TM = Fe, Co, Cr) crystals grown by vertical Bridgman method. The crystal structure of the grown crystals was zinc-blende, which wa ...
We have studied the optical, magnetic, and magneto-optical properties of diluted magnetic semiconductor Cd1-x-yMnxTMyTe (TM = Fe, Co, Cr) crystals grown by vertical Bridgman method. The crystal structure of the grown crystals was zinc-blende, which was examined by XRD measurements and the mole fraction of a transition metal was determined by EPMA and XRD. The lattice constant decreases linearly with increasing TM contents y. The decrease in the lattice constant is due to the smaller Mn (a = 1.326 Å), Fe (a = 1.170 Å), Co (a = 1.225 Å), and Cr (a = 1.2807 Å) covalent radii compared with Cd (a = 1.405 Å). The equations of the lattice constants for samples added different TM atoms to ternary Cd1-xMnxTe compound were a = 6.485-0.146x-0.139y (Fe), a = 6.485-0.146x-0.236y (Co), and a = 6.485-0.146x-0.231y (Cr), respectively, which obeyed Vegard’s law well.
The bandgap energy was depended on y linearly and blue-shifted with decreasing T. The increase of the energy gap with y may be due to a decrease in the lattice constant.
The photoluminescence on the Cd1-x-yMnxTMyTe for a series of TM compositions was measured over the temperature range of 12~300 K. From the temperature dependence of the bound exciton peak, the Varshni temperature parameter was found to increase linearly with increasing Mn concentration x and TM concentration y, while β decreased with x and y.
We compared the FWHM of the measured PL emission spectra for our samples with the calculated FWHM due to alloy broadening. The complex dielectric functions of Cd1-x-yMnxTMyTe were measured using spectroscopic ellipsometry in the range of 1.3 ~ 6.0 eV photon energy at room temperature. From the fitting with the SCP model, we obtained the energies E0, E1, E1+d1, and E2 with various TM concentration y and calculated the spin-orbit splitting energies. The E1, E1+d1, and E2 energies were decreased with increasing TM composition, which is due to the hybridization effect of the valence and conduction bands in Cd1-xMnxTe with TM 3d levels.
The magnetic and transport properties of Cd1-x-yMnxTMyTe single crystals were investigated.
For Cd1-xMnxTe compounds, for x<0.2 are paramagnetics; for 0.2<x<0.60 spin-glass phase; and for 0.60<x<0.82 antiferromagnetically ordered by low-field magnetic susceptibility measurements.
The Cd0.63-yMn0.37CoyTe crystals showed the ferromagnetic ordering up to 300 K and n type conductivity by the addition of Co. The magnetic susceptibility per Fe mole of Cd1x-yMn0.38FeyTe increases with increasing Fe concentration, which is same as that of CdMnTe.
The Cd0.562Mn0.38Fe0.058Te crystal showed the peculiar magnetic behavior, i.e. the temperature dependent magnetic susceptibility in 100 Oe above Tc (=20.1 K). The Cd0.64-yMn0.36CryTe crystals showed ferromagnetic up to 350 K. The coercive field was 42 Oe at 300 K for Cd0.55Mn0.36Cr0.09Te crystal and the coercive field increased with Cr-addition. Although the measured magnetic moment per Cr atom for Cd0.64-yMn0.36CryTe low y at 1 T was very low, the magnetic moment was rapidly increased with increased Cr-addition. To investigate the Faraday rotation for Cd1-x-yMnxTMyTe, the Verdet constants were measured at 10 K-300 K and the Faraday rotation of Cd1-x-yMnxTMyTe was found to be much larger than that of CdMnTe crystals. The enhancement of the quaternary samples compared with ternary Cd1-xMnxTe compounds in the Faraday rotation was able to be summarized in terms of the sp-d exchange content and the magnetic susceptibility.