Abstract
We report the dependence of magnetoresistance effect on resistivity (ρ) in Co/ZnO films deposited by magnetron sputtering at different sputtering pressures with different ZnO contents. The magnitude of the resistivity reflects different carrier transport regimes ranging from metallic to hopping behaviors. Large room-temperature magnetoresistance greater than 8% is obtained in the resistivity range from 0.08 to 0.5 Ω · cm. The magnetoresistance value decreases markedly when the resistivity of the films is less than 0.08 Ω · cm or greater than 0.5 Ω · cm. When 0.08 Ω · cm < ρ < 0.5 Ω · cm, the conduction contains two channels: the spin-dependent tunneling channel and the spin-independent second-order hopping (N = 2). The former gives rise to a high room-temperature magnetoresistance effect. When ρ > 0.5 Ω · cm, the spin-independent higher-order hopping (N > 2) comes into play and decreases the tunneling magnetoresistance value. For the samples with ρ < 0.08 Ω · cm, reduced magnetoresistance is mainly ascribed to the formation of percolation paths through interconnected elongated metallic Co particles. This observation is significant for the improvement of room-temperature magnetoresistance value for future spintronic devices.
Highlights
The investigation of electron spin transport from metallic ferromagnets to semiconductors has been an active research field in spintronics in the past two decades [1,2,3]
We studied a large number of Co/ZnO films deposited at different sputtering pressures with different ZnO thicknesses and found that the MR effect is strongly dependent on the resistivity of films
The key result of our work is presented in Figure 1, which clearly shows that the room temperature (RT) MR is strongly correlated with resistivity and the transport behavior of Co/ZnO films
Summary
The investigation of electron spin transport from metallic ferromagnets to semiconductors has been an active research field in spintronics in the past two decades [1,2,3]. The manipulation of carrier spins between magnetic metals and semiconductors provides improved functionality of spintronic devices such as magnetic sensors, spin transistors, and magnetic memory cells [4,5]. Spin injection into a semiconductor reveals low efficiency in ferromagnetic metal/semiconductor films at room temperature (RT) because of a significant mismatch in conductivities [6,7,8]. Magnetic metal/semiconductor films have been considered for their large magnetoresistance (MR) at RT, which is responsible for effective spin injection into semiconductors [9,10,11,12,13,14]. Yan et al reported a large negative MR of 11%
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