X.-G. Zhang

Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films.

Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. Here, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. In this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices.

Thickness dependence of magnetic and transport properties in organic-CoFe discontinuous multilayers

Spin-dependent transport measurement in 3-hexadecyl pyrrole (3HDP) with a CoFe layer and the current-in-plane geometry is reported. Transport properties indicate the CoFe layers are discontinuous when their thicknesses are smaller than 6 nm. The temperature dependence of the conductance suggests that the transport mechanism is likely small polaron hopping. The observed positive magnetoresistance ratio at low temperature gives evidence of spin-conserving transport.

Spin dependent tunneling and interface characterization in epitaxial Fe/MgO/Fe magnetic tunnel junctions

This paper presents huge tunnel magnetoresistance (TMR) effect in epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs) at room temperature predicted by first-principle theory. Surface X-ray diffraction, Auger electron spectroscopy, X-ray absorption spectra, and X-ray magnetic circular dichroism is used for interface characterization. The interfacial structure plays a crucial role on coherent tunneling in epitaxial MgO-based MTJs grown by molecular beam epitaxy.

Electrical Conductivity of Inhomogeneous Systems: Application to Magnetic Multilayers and Giant Magnetoresistance

Recently there has been great interest in the transport properties of layered magnetic materials because of the discovery of a new form of magnetoresistance1 called the giant magnetoresi stance (GMR). GMR is a change in the electrical resistivity of a magnetically inhomogeneous material that occurs when the application of a magnetic field brings the moments in different regions into alignment. GMR has been observed in several geometries, but the most promising and interesting GMR systems are composed of thin layers of ferromagnetic material separated by non-magnetic or very weakly magnetic spacer layers. For layered GMR systems, electric fields are usually applied so that the current flows parallel to the layers. This “current in the plane” geometry will be assumed in this paper.