Synthesis of inverted spinel ferrite nanocrystals inside ZnO by ion implantation and post-annealing

The hybrids of magnets and semiconductors show promising magneto-transport properties, and would enable the development of spin-dependent magneto-electronic and magneto-optic devices [1]. The most well studied system is MnAs/GaAs due to its chemically stable interface and the possibility of epitaxy [2]. Large magneto-resistance and Faraday rotation have been observed in GaAs with MnAs nanoclusters. However the Curie temperature of MnAs is 313 K, and limits its application at high temperatures. Spinel ferrites are a group of materials with similar crystal-structure and rich magnetic as well as electronic properties, e.g. NiFeO and CoFeO, are ferrimagnets with large Neel temperatures. Therefore the hybrids of spinel ferrites with semiconductors would allow versatile possibilities for spin-dependent devices. However the integration of ferrites with semiconductors remains challenging due to the fact that the growth of ferrites requires high temperatures and oxygen environment, which is detrimental to conventional semiconductors like Si and GaAs [3]. In this contribution, we show the possibility to incorporate inverted spinel ferrite nanocrystals with ZnO by ion implantation and post-annealing. Their magnetic and electronic properties were investigated by SQUID and x-ray absorption spectroscopy. These nanocrystals are crystallographically oriented inside ZnO, and show superparamagnetic characteristics. Large positive magneto-resistance has been observed, and we will discuss its origin with respect to ordinary magneto-resistance and to magnetic scattering by nano-ferrites. Our results suggest a new magnet-semiconductor heterostructure with potential application in magneto-electronics and microwave devices [3].

[1] G. Prinz, Science 250, 1092 (1990).
[2] L. Daweritz, Rep. Prog. Phys. 69, 2581 (2006).
[3] Z. Chen et al., Appl. Phys. Lett. 91, 182505 (2007).