Simply the best

Magnetic tunnel junctions that show large magnetoresistance changes and excellent temperature stability can be produced using a simple sputtering method.

Credit: © 2009 AIP

Spintronic devices based on a thin insulating layer sandwiched between two ferromagnetic electrodes — magnetic tunnel junctions — show extremely large tunnelling magnetoresistance (TMR) that approaches 400% at 300 K. However, despite these massive changes in resistance under external magnetic bias fields, such devices show large temperature fluctuations and, significantly, these characteristics are only observed in devices produced using molecular beam expitaxy — an expensive and complicated means of growing the structures. Wenhong Wang and colleagues at the National Institute for Materials Science, Tsukuba, Japan, have now fabricated magnetic tunnel junctions that show room temperature tunnelling magnetoresistance of 330% and a record-breaking output voltage of 425 mV, using a simple argon-ion sputtering method¹.

The structure of the magnetic tunnel junction devices consisted of a Co₂FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO(001) substrate. The crystalline quality of the bottom Co₂FeAl layer, which was deposited at room temperature, and the thickness of the MgO were critical parameters for producing a large tunnelling magnetoresistance ratio. The highest room temperature tunnelling magnetoresistance of 330% was obtained for devices annealed at 450 °C with a 1.8-nm thick MgO layer.

Notably, the temperature dependence of the tunnelling magnetoresistance ratio for the devices was much less than epitaxial devices produced by more intricate and expensive methods.