Spin glass behavior and colossal negative magnetoresistance of the p-Zn_(1-x)Mn_xTe strongly doped with phosphorus

摘要

Magnetoresistance, ac and dc magnetization, and photoluminescence (PL) experiments have been performed on the p-type Zn_(0.99)Mn_(0.01)Te and Zn_(0.97)Mn_(0.03)Te alloys strongly doped with phosphorus (P). The investigated samples exhibit spin glass behavior with ferromagnetic regions near the freezing temperature T_f = 1.9 K and colossal negative magnetoresistance (negMR) of 2.2 × 10~3 times at 4.2 K for 0 ≤ B ≤ ±6 T. The negMR curves contain occurrences of hysteresis providing evidence for the memory effect. Looking for possible ferromagnetic interactions responsible for the spin glass behavior at low hole densities, we observe in PL spectra that the P doping quenches internal recombination in Mn~(2+) ions. This strongly indicates a charge transfer between Mn~(2+) and P~(2-) ions leading to the creation of Mn~(3+) and P~(3-) ions. The creation of Mn~(3+) is confirmed by an observation of strong PL enhancement at excitation energies lower than the band gap and PL study at various temperatures. The resulting simultaneous existence of the mixed valence Mn~(2+) and Mn~(3+) ions can lead to double exchange mechanism of ferromagnetic interaction. Also, Mn~(3+) ions can exhibit a superexchange interaction leading to local ferromagnetic phases.