Effect of interface roughness on the magnetotransport behaviour of NiO/Co/Cu/Co bottom spin valves
|Paolo Allia 2, Alessandro Chiolerio 1,4, Marco Coisson 3, Elena S. Olivetti 1,4, Federica Celegato 2, Luca Martino 3, Candido F. Pirri 1,4, Denis Perrone 1,4, Paola Tiberto 3|
1. Dipartimento di Fisica, Politecnico di Torino, corso Duca degli Abruzzi, 24, Torino 10129, Italy
Antiferromagnetic (AF)/ferromagnetic (FM) exchange-coupled systems are widely used as active elements in devices based on giant magnetoresistance (GMR). The strict dependence of the AF exchange coupling on the spacer layer thickness requires fine control of deposition rate during film growth. Usually, sputtering deposition is exploited to prepare multilayers consisting of alternated ferromagnetic and nonmagnetic (NM) metals.
In this work, thermal evaporation under vacuum has been checked as an alternative technique for multilayered films growth. Bottom spin valves of the family NiO/Co/Cu/Co with an AF layer of 100 and 140 nm and a 5/2/6 nm trilayer have been produced and characterised. The AF has been synthesized by thermal oxidation of Ni films and annealed in a magnetic field of 23 Oe.
Magnetotransport measurements were performed by the four points method in the temperature range 5–200 K, under a field up to 70 kOe. The observed GMR amplitude at T=5 K is about 2 ‰ for all the studied samples. In some samples, the GMR – an effect typically arising at FM-NM interfaces - is associated to a contribution from anisotropic magnetoresistance – a bulk effect originating within each FM layer.
Hysteresis loops were measured by Alternating Gradient Magnetometry under a field up to 20 kOe. The multilayer coercivity has been found to increase with the thickness of the AF layer.
AFM pictures show that surface roughness closely reproduces the AF underlayer’s one , being about one order of magnitude larger than that of the metallic trilayer deposited directly on Si (1-3 nm). This value considerably exceeds the ones typically reported for sputter-deposited NiO  and is thought to be the cause of the very low observed GMR amplitude.
The role of interfacial roughness on the ratio between surface-to-bulk magnetoresistance amplitudes is discussed.
 W.F. Egelhoff Jr. et al. Progr. Surf. Sci. 67 (2001) 355-364
 D.G. Hwang et al. JMMM 186 (1998) 265-276
Presentation: poster at E-MRS Fall Meeting 2005, Symposium D, by Alessandro Chiolerio
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-20 09:54 Revised: 2009-06-07 00:44