Enhancement of zinc vacancies in room-temperature ferromagnetic Cr–Mn codoped ZnO nanorods synthesized by hydrothermal method under high pulsed magnetic field

Room-temperature ferromagnetic Cr–Mn codoped ZnO diluted magnetic semiconductor was synthesized by pulse magnetic field-assisted hydrothermal method. X-ray diffraction and Raman spectra analysis reveal that all the samples have hexagonal wurtzite structure. High resolution transmission electron microscopy and Energy-dispersive spectroscopy measurements ensure that the Cr and Mn ions are incorporated into the wurtzite host matrix without any detectable impurity phase. X-ray photoelectron spectroscopy confirms that Mn and Cr ions are doped into the ZnO wurtzite host matrix with divalent states in the sample without magnetic field processing. Cr ions became trivalent states in ZnO synthesized with high pulsed magnetic field, while Mn keeps its divalent state. The presence of Cr³⁺ is attributed to hole doping in ZnO with zinc vacancies induced by the field. Magnetization measurements reveal the appearance of ferromagnetism for the magnetic field processed sample. Comparing with oxygen vacancies, zinc vacancies (hole doping) is more effectively to stabilized ferromagnetism in Mn-doped ZnO diluted magnetic semiconductors. - Graphical abstract: This figure shows the magnetization versus magnetic field curves for ZnO–Cr–Mn-0T and ZnO–Cr–Mn-4T at 290 K. The 4 T sample was well-defined hysteresis loops, which is indicative of room-temperature ferromagnetic behavior. But for 0 T sample, no ferromagnetic response at 290 K is observed. The hole doping enhanced by high pulsed magnetic field is crucial to stabilize ferromagnetism in Mn-doped ZnO diluted magnetic semiconductor. And the presence of Cr³⁺ in 4 T sample is a possible signature of hole doping induced by zinc vacancies. - Highlights: • Cr–Mn codoped ZnO nanorods were synthesized by hydrothermal method. • High pulsed magnetic field was applied during the hydrothermal method. • The valence state of doped elements was investigated by XPS. • High pulsed magnetic field enhances the concentration of zinc vacancies. • Hole doping is the key factor in Mn-doped ZnO diluted magnetic semiconductors