Co-rich magnetic amorphous films and their application in magnetoelectronics

Abstract

Three kinds of Co-rich magnetic amorphous films of CoFeB, CoFeNiSiB, and CoFeHfO were prepared by magnetron sputtering and applied as soft ferromagnetic ͑FM͒ electrodes in tunneling magnetoresistance ͑TMR͒ devices. Initial results exhibit a large room-temperature TMR effect of approximately 50%. The high effect can be attributed to interfacial coherence between the amorphous barrier-electrode layers and, accordingly, suggests a high local spin polarization possibly associated with strong nearest-neighbor spin correlations of the magnetic atoms. The magnetotransport behavior may be governed by details of the local spin environment in magnetic amorphous electrodes due to their short electron mean-free path ͑ϳ3-5 Å͒. The annealing effect on TMR was found to be more pronounced due to the atomic cooperative structural relaxation and more thermally stable compared with the polycrystalline electrode junctions. Additionally, the use of the magnetic oxide electrode CoFeHfO has shown that the relevant FM electrode-barrier interface becomes insensitive to the oxygen, which simplifies the oxidation process used for the oxide barrier fabrication.

Temperature dependence of magnetoresistance in magnetic tunnel junctions with different free layer structures

“…From previous studies, the films with thicknesses in this range may be superparamagnetic, nonmagnetic, or ferromagnetic. [28][29][30][31] The thin free layer of our type 1 MTJ samples is mostly ferromagnetic, which shows hysteresis. Since the free layer of type 1 is 5 times thinner than that of type 2, we would then expect there to be more defects in the free layer of type 1 than in that of type 2.…”

Thermal annealing of junctions with amorphous and polycrystalline ferromagnetic electrodes

“…Indeed, from the atomic force microscopy images, a barrier roughness of 0.24 nm rms is extracted for MTJ1 and MTJ2 and 0.20 nm rms for MTJ3 (Fig. 8 For MTJ1 and MTJ2, in the annealing temperature window from T a = 175-300°C, an almost constant exchange bias of the AAF is achieved. (ii) The larger saturation magnetization, M S , of the CoFe compared to CoFeB.…”

Nanoscale diffusion in amorphousFe75Zr25films

“…1,2 Because of the absence of long-range order, they possess isotropic properties and are potential candidates for future applications in microsized mechanical devices. 3 The absence of grain boundaries also makes them useful as diffusion barriers in microchip fabrication. 4,5 However, the amorphous phase is metastable in nature and thermal annealing may cause structural relaxation and/or its transformation to stable crystalline phases, resulting in drastic changes in almost all of its physical properties.…”

“…[1][2][3][4][5] Due to the absence of grains and grain boundaries, amorphous films generally have low surface roughness and thus present sharper interfaces in multilayer structures. As a result, they find increasing applications in spin valve and tunnel magnetoresistance devices.…”