Pinhole Coupling Strength in Giant Magnetoresistance Spin Valves: A Statistical Approach
D X. Yang, E J. Repetski, H D. Chopra, B J. Spencer, D Parks, P J. Chen, William F. Egelhoff Jr.
The nature of pinhole coupling and its strength in 'giant' magnetoresistance (GMR) spin valves is far from understood. In the present study, a statistical model has been developed that correctly predicts the coupling strength due to pinholes, using the NiFe/Cu/Co/NiO-based top spin valves. Tribologists have long studied the statistical properties of surfaces, and the statistical model for pinhole coupling is based on that inspiration. The model highlights the fact that a negative covariance between the interfaces of a GMR spin valve (or any multilayer in general) is a requisite for the formation of pinholes. If the two surfaces that bound the Cu layer have a negative covariance, the variation in the copper spacer thickness then leads to a finite probability of a peak and a valley coinciding together, resulting in the formation of a pinhole. To test the valididty of the statistical model, top spin valves of the type NiFe/Cu/Co/NiO were deposited as a function of Cu spacer thickness on oxidized silicon substrates coated with different seed layers. Different wetting characteristics of different seed layers lead to different roughness of the seed layer coated substrates. Deposition of overlayers of spin valves over different seed layer coated substrates thus provides a means of varying the population of the pinholes as a function of Cu spacer thickness. The results of the statistical model were compared with the coupling in samples of deposited on three different seed layers, namely, (i)(Pt (20nm)), (ii) No seed layer, (iii) ((Ta(5nm)/Pt (20 nm)/Ta (5nm)); for each seed layer, the Cu layer thickness was varied from 1.5nm to 5nm. The coupling values predicted from the statistical model have been shown to compare favorably with the experimentally observed coupling values. The present study also shows that Neel's orange-peel coupling is not only inadequate in explaining the observed coupling in spin valves, but also would require microstructure features that are opposite to that required for pinholes.
Physical Review B (Condensed Matter and Materials Physics)
, Repetski, E.
, Chopra, H.
, Spencer, B.
, Parks, D.
, Chen, P.
and Egelhoff Jr., W.
Pinhole Coupling Strength in Giant Magnetoresistance Spin Valves: A Statistical Approach, Physical Review B (Condensed Matter and Materials Physics)
(Accessed March 2, 2024)