Activation of room temperature ferromagnetism in ZnO thin films for spintronics applications

The manipulation of the spin degree of freedom of electrons in semiconductor devices is an attractive issue due to the key role of these materials in technological devices. Among the semiconductors, ZnO has been considered to be the most promising candidate for fabrication of spintronic devices due to its high solubility for transition metal (TM) ions. Further, its magnetic, electric and optoelectronic properties can be optimized via surface functionalization with different organic molecules. To observe room temperature ferromagnetism in ZnO films, we have adopted different approaches, viz. doping of magnetic ions, ion irradiation on ZnO films and surface functionalization of ZnO with different organic molecules. 
Among other ZnO based DMSs, ZnO:V appears to be one of the most promising systems for spin polarization. An attempt is made to observe RTFM in V doped ZnO films grown by RF sputtering with optimized experimental conditions. The observed ferromagnetism in V doped ZnO films are explained by bound magnetic polaron (BMP) model. From an experimental perspective, the structural defects influence ferromagnetic ordering in oxide based nanostructures. Swift heavy ion (SHI) irradiation is known to introduce controlled defects in crystalline materials which can modify the structural, optical and magnetic properties. The enhancement of RTFM in V doped ZnO films on ion irradiation are attributed to the increase of defects such as oxygen vacancies. The ferromagnetic behaviour in ZnO nanostructures functionalized with organic molecules has stimulated the development of a new class of magnetic semiconductor nanostructures for various applications. The activation and enhancement of RTFM in pure and V doped ZnO films are manifested on Thiol, amine and TOP functionalization. The enhanced ferromagnetic behaviour in thiol, amine and TOP functionalization are attributed to charge redistribution occurring in the ZnO film surface due to the difference in electronegativity of the S atom in the thiol, N atom in the amine and P atom in the TOP at the surface of ZnO. Activation of RTFM in PLD grown pure ZnO films were achieved by varying oxygen pressure and enhancement in magnetization was found on thiol functionalization. The combination of band gap engineering and the integration of magnetic degrees of freedom offer remarkable opportunities for a new generation of spin based devices.