The contribution of x-ray specular reflectometry to the oxygen-induced magnetic properties in Pt/Co/AlOx

Abstract

Two key parameters were analyzed in Si/SiO/Pt/Co/AlOx: the oxidation time of the Al layer resulting in AlOx, and the ex situ annealing temperatures varied in the 15 and 55 s and 20, 300, and 450 °C ranges, respectively. For intermediate annealing temperatures (∼300 °C), the quantitative analysis of specular reflectometry data shows that the progressive oxidation of layers by increasing the oxidation time goes along with an improvement of the homogeneity of the alumina layer. This outcome casts new light on the temperature dependence of magnetic properties of the samples. The remarkable temperature variation of the coercive field, extracted from extraordinary Hall effects in the 5–300 K range, is associated with structural change due to Co–oxygen bondings, which leads to strong pinning of Co spins in the low temperature regime.

Competition between CoOx and CoPt phases in Pt/Co/AlOx semi tunnel junctions

“…47 This explains why CoO is induced for as-grown samples, and that annealing favors the appearance of Co 3 Pt. Now, we discuss the room temperature magnetic properties of the system at the light of our structural results: 23,26 (i) For as-deposited samples and increasing t Ox , a crossover between Pt/Co/Al/AlO x and Pt/Co-CoO x /AlO x stacks is observed. In particular, t à Ox ¼ 40 s appears to be a reasonable oxidation time for obtaining a highquality AlO x layer (both maximized Th and q), but with marked roughnesses for the different layers.…”

“…The influence of a ferromagnetic/antiferromagnetic (Co-CoO x ) coupling is also observed in the low temperature regime of magnetic properties. 26,48 In addition, Rodmacq et al 23 found that the amplitude of the Hall resistance considerably decreases for the longest oxidation times. 23 We show here that it is explained by the appearance of CoO x .…”

“…Recently, preliminary XRR results have confirmed the formation of CoO and AlO x phases by varying both t Ox and T Ann for some isolated trilayers. 25,26 However, the origin of Perpendicular Magnetic Anisotropy (PMA) is not clear: Is there oxygen at the interfaces between Co and AlO x ? Is there a CoPt intermixing caused by the annealing?…”

Impact of organic capping layer on the magnetic anisotropy of ultrathin Co films

“…The tunneling properties and the stability of the magnetic tunneling junctions strongly depend on the structural and magnetic arrangement of the electrodes and barrier material. Several studies demonstrated an influence of nonmagnetic metals (NM) cover layers on the interfacial PMA of Co [10,11,12,13]. It has been recognized, that the effect is determined by the orbital moment anisotropy of Co and could be modified by an interface hybridization of the NM layer (e.g., its d or p orbitals) with Co 3d orbitals [14,15,16,17].…”