Anisotropic ferromagnetism in substituted zinc oxide

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Ferromagnetism in diluted magnetic semiconductors (DIMS) is typically observed at low temperatures.
• Achieving room-temperature ferromagnetism in oxide materials remains a significant challenge.
• Understanding the mechanisms behind ferromagnetism in doped oxides is crucial for spintronic applications.

Purpose of the Study:

• To investigate the possibility of achieving room-temperature ferromagnetism in (110) oriented ZnO films.
• To identify which dopant elements induce ferromagnetism and quantify the magnetic moments.
• To elucidate the underlying physical model responsible for the observed ferromagnetism.

Main Methods:

• Fabrication of (110) oriented ZnO films doped with various 3d transition metal ions (Sc, Ti, V, Fe, Co, Ni, Cr, Mn, Cu) at 5 at. %.
• Characterization of magnetic properties, including measurements of magnetic moments and anisotropy.
• Theoretical interpretation using a spin-split donor impurity-band model.

Main Results:

• Room-temperature ferromagnetism was observed in ZnO films doped with Sc, Ti, V, Fe, Co, and Ni, but not Cr, Mn, or Cu.
• Significant magnetic moments were measured, such as 2.6 µB for Co and 0.5 µB/atom for Ti.
• Magnetization exhibited strong anisotropy, varying up to a factor of 3 with field orientation.

Conclusions:

• The spin-split donor impurity-band model successfully explains ferromagnetism in both insulating and conducting high-k oxides.
• Observed magnetic moments are attributed to two-electron defects and unpaired 3d electrons of dopant ions.
• This work demonstrates a viable route to room-temperature ferromagnetism in doped ZnO for potential spintronic devices.