Homogeneous versus composite ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ crystals: Magnetic interactions and transport properties

We present the studies of structural, magnetic, and magnetotransport properties of ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ crystals with the average Mn contents $x$ changing from 0.013 to 0.170 and Zn contents $y$ varying from 0.002 to 0.051. Homogenous distribution of Mn ions is observed for the samples with $x\le 0.025$. The presence of MnAs clusters in the studied alloy for $x>0.025$ induces room-temperature ferromagnetism with the Curie temperature $T_C$, with values around $325\mathrm{K}$. High crystal quality leads to high carrier mobility values observed for all of our samples, as high as $7100{\mathrm{cm}}^2/\left(\mathrm{V}\mathrm{s}\right)$ for $x=0.025$ and $y=0.028$. The Shubnikov–de Haas oscillations are observed at $T\le 50$ K for all of our samples. The oscillations allowed the calculation of the effective mass $m^{*}$, giving values of about $0.11–0.12m_e$. The presence of magnetic impurities has a strong influence on the magnetoresistance of the alloy. For the samples with $x\ge 0.076$, the Shubnikov–de Haas oscillations are observed on the background of a strong linear positive magnetoresistance, present up to room temperature. The maximum values of the linear positive magnetoresistance are close to 200% for the sample with $x=0.170$ and $y=0.002$, at $T=1.5\mathrm{K}$. This positive magnetoresistance is related to the presence of MnAs clusters in the semiconductor lattice.

Figure 1

X-ray diffraction patterns obtained for the representative ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ sample with $x=0.087$ and $y=0.007$. (a) Full range of $2\theta$ angles, (b) magnified high-angle part of this pattern, and (c) magnification of the part of pattern in which reflections from foreign phases were observed.

Figure 2

Results of the SEM/EDX measurements obtained at room temperature for the representative ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ sample with $x=0.087$ and $y=0.007$ including the following: (a) SEM image and (b)–(f) EDX microprobe results, including (b)–(e) maps of the distribution of the alloying elements and (f) the results of detailed chemical-content measurements done at different spots [marked as numbers in (a)] of the sample surface.

Figure 3

Temperature dependence of the real part of the ac magnetic susceptibility obtained for the selected ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ samples with different average Mn and Zn contents $x$ and $y$, respectively.

Figure 4

Temperature dependence of the resistivity, ${\rho }_{xx}$, obtained for the selected ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ samples with different Mn and Zn contents, $x$ and $y$.

Figure 5

Temperature dependence of the inverse of the ac and dc magnetic susceptibility obtained for the selected ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ samples with different Mn and Zn contents, $x$ and $y$ (markers), and fitted to the Curie-Weiss law with Eq. (1) (lines).

Figure 6

Results of the isothermal magnetization studies for the selected ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ samples with different Mn and Zn contents, $x$ and $y$, including: (a) magnetization as a function of the applied static magnetic field at $T=4.5\mathrm{K}$, (b),(c) magnetization hysteresis curves measured at (b) $T=4.5\mathrm{K}$ and (c) $T=300$ K.

Figure 7

Selected results of the magnetoresistance measurements obtained for our ${\mathrm{Cd}}_{1-x-y}{\mathrm{Mn}}_x{\mathrm{Zn}}_y{\mathrm{SnAs}}_2$ crystals with different Mn and Zn contents, $x$ and $y$, including (a) selected representative MR curves obtained for the sample with $x=0.025$ and $y=0.028$ (inset: SdH oscillations with quadratic contribution removed), (b) the SdH oscillation peak number vs the inverse of the magnetic field, obtained from the experimental results (symbols) and fitted with linear functions (lines) for the selected samples with different chemical contents, $x$ and $y$, (c) selected typical MR curves obtained at $T\approx 1.6\mathrm{K}$ for the samples with different chemical contents, $x$ and $y$ (inset: selected SdH oscillations with linear contribution removed), and (d) amplitude of the SdH oscillations, obtained experimentally for the representative sample with $x=0.025$ and $y=0.028$ (symbols) and fitted with the use of linear function (lines) [inset: the amplitude of the SdH oscillations as a function of temperature obtained for the sample with $x=0.104$ and $y=0.028$ (symbols) and fitted to Eq. (5) (line)].