Tunneling Magnetoresistance of Co Granules in AlN/Co/AlN Type Discontinuous Films

Abstract

Magnetic transport phenomena in rf sputtered AlN/Co type ten-layered discontinuous films of nanoscaled [AlN(3 nm)/Co(t nm)]...(10) with t(Co) = 1.0 similar to 2.0 nm have been investigated. The nanostructures and tunneling magnetic resistance of the samples are strongly dependent on the thickness of the Co layer. Negative tunneling magneto-resistance due to the spin-dependent transport has been observed along the current-in-plane configuration in the samples having the Co layers below 1.6 nm thick. When the thickness of Co layer was less than 1.2 nm, randomly oriented granular Co particles were completely isolated and embedded in an amorphous AlN matrix, and the films showed the superparamagnetic behavior with a high MR, value of Deltarho/rho(0) = 3.5%. As t(Co) increases, a transition from the regime of co-existence of superparamagnetic and ferromagnetic behaviors to ferromagnetic behavior was observed. The tunneling barrier "decay length for tunneling" for films having a Co layer thickness from 1.4 to 1.6 nm was measured to be in the range from 0.004 to 0.021 Angstrom(-1). An enhanced TMR. was observed after annealing which is subscribed to an increase of about 100% in activation energy for tunneling.