UC Berkeley

Nanomagnetic devices in -The sub-5-nm size range still do not exist, not only because of many fabrication and characterization challenges but also because of -The poorly understood physics in this size range. Previous experimental studies from various groups have shown that -The spin relaxation time can be increased by orders of magnitude with this size reduction. The increased spin lifetime leads to a combination of effects such as spin accumulation and tunneling magnetoresistance enhancement which in turn can significantly and favorably affect -The device performance [1]. The goal of this study is to exploit this new physics through fabrication and testing of magnetic tunneling junction (MTJ) devices with a characteristic size of below 5 nm. To achieve this goal, we integrate magnetic nanoparticles into MTJ structures and measure -Their key properties such as I-V curves and magnetoresistance dependencies. The nanoparticles, with sizes ranging from below 2 to over 10 nm, are made of -The ferrimagnetic spinel ferrite CoFe2O4 using co-precipitation chemistry. It has been -Theoretically predicted that -These nanoparticles become half-metallic in this size range and thus can lead to unprecedented high magnetoresistance values. Indeed, -The nanodevices under study display spin-filtering properties, as confirmed through measurements of magnetoresistance and I-V dependences [2]. This paper summarizes -The measured room-temperature anomalous magnetoresistance and I-V curves with a Coulomb-staircase-like dependence characteristic of a single-electron transport.