Resonant inversion of tunneling magnetoresistance using MgO/NiO barriers

摘要

Magnetic tunnel junctions (MTJs) are promising devices for data storage and field sensor applications. MTJs with MgO tunnel barriers and Co-Fe ferromagnetic electrodes exhibit giant tunneling magnetoresistance (TMR) effects which can exceed 350% at room temperature[1]. The TMR of these MTJs typically increases with anneal treatments likely due to improved properties of the tunnel barrier and the interface between the barrier and the ferromagnetic electrodes. However, the TMR is observed to decrease drastically above some characteristic annealing temperature, typically above ～400°C in MTJs exchanged biased using IrMn and PtMn antiferromagnetic layers. One reason might be due to diffusion of Mn from these layers into the barrier, possibly leading to the formation of Mn oxide [2]. In addition to Mn oxide, it is also possible that other oxides are formed at the interface between the MgO barrier and the ferromagnetic electrodes, for example, CoO. For these reasons we have explored the properties of MTJs in which we have inserted thin insulating antiferromagnetic (AF) layers formed from oxides of Mn, Ni and Co at the MgO interfaces. These oxides have similar simple cubic structures to MgO and grow epitaxially on MgO (100). In this paper we report the magneto-transport properties, as a function of temperature and bias, of MTJs grown with barriers formed from double layers of MgO and NiO, CoO or MnO as well as triple layers of MgO/NiO, CoO and MnO/MgO.