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 [1], 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 [2] 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.

[1] W.F. Egelhoff Jr. et al. Progr. Surf. Sci. 67 (2001) 355-364

[2] D.G. Hwang et al. JMMM 186 (1998) 265-276

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/3681 must be provided.

1. Low-temperature magnetic softening in sputtered FePtAg granular multilayers
2. Fabrication and characterisation of arrays of submicrometric magnetic dots