Magnetic and Electrical Properties of the ZnGeAs2 : Mn Chalcopyrite

2124KOROLEVA et al.41431212M, emu/g21T = 5 K25 K50 Kρ · 10 2 , Ω cm1081110R h · 10 2 , cm 3 /C0 10 20 30 40 50H, kOeFig. 4. Magnetization isotherms of the ZnGeAs 2 samplewith 3.5 wt. % Mn at different temperatures. Each curvewas measured after the sample had been cooled to 5 K in azero magnetic field.60 50 100150 200 250 300T, K9Fig. 5. Temperature dependence of the electrical resistivityρ and the normal Hall coefficient R H for the ZnGeAs 2 samplewith 1.5 wt. % Mn.romagnetic phase depends on its configuration, whichvaries with temperature. Therefore, for the Curie pointwas taken the temperature obtained by extrapolation ofthe steepest part of the M(T) curve measured in themaximum field reachable (50 kOe) to its intercept withthe temperature axis. The Curie temperature was foundto be 367 K. This is the highest Curie temperaturefound thus far in the II–IV–V 2 : Mn systems. This providedsubstantiation for the theoretical suggestion [10]that the Curie temperatures of Zn-containing chalcopyritesshould be higher than those of the correspondingCd-based ones.The Hall electric field of the samples under studywas found to depend linearly on magnetic field, whichevidences the absence of anomalous Hall effect. Measurementsof the electrical resistivity and of the Halleffect revealed that all the samples support hole conduction,with the hole concentration p ~ 10 19 –10 20 cm –3and mobility varying from 0.25 to 2.5 cm 2 V –1 s –1 . Figures5 and 6 plot the temperature dependences of theelectrical resistivity ρ, normal Hall coefficient R H andmobility. We readily see that the ρ(T) relation of the1.5 wt. % Mn composition follows a pattern characteristicof semiconductors, while the p(T) curve has apurely metallic signature, with p varying very little,from 6.4 × 10 19 cm –3 at T = 50 K to 5.2 × 10 19 cm –3 at300 K. The mobility grows faster, from 1.25 cm 2 V –1 s –1 at20 K to 2.6 cm 2 V –1 s –1 at 300 K. In the 3.5 wt. % Mncomposition, ρ(T) passes through a minimum at T ~30 K, and the mobility increases by an order of magnitudein the region 10 ≤ T ≤ 300 K, whereas p varies from2.5 × 10 20 cm –3 at 50 K to 8 × 10 19 cm –3 at 300 K. Themagnetoresistance is small; it does not exceed 4% atH = 8 kOe.The origin of ferromagnetism in dilute magneticsemiconductors was studied by first-principles electronicstructure calculations [11, 12]. It is maintained[11, 12] that the effective exchange interaction in thesecompounds derives primarily from competitionbetween double exchange and superexchange interactions.It is known that semiconductors with chalcopyritestructure are stabilized by internal defects acting assources of holes which form stable complexes with Mnρ · 10 3 , Ω cm34302622180 50 1003.53.02.52.01.51.00.50150 200 250 300T, KFig. 6. Temperature dependence of the electrical resistivityρ and the hole mobility for the ZnGeAs 2 sample with3.5 wt. % Mn.µ, cm 2 /V sPHYSICS OF THE SOLID STATE Vol. 49 No. 11 2007