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

Abstract

10 pagesInternational audienceWe report on the evolution of the structure and composition of a Pt(3 nm)/Co(0.6 nm)/AlOx(2 nm) trilayer sputtered on Si/SiO2 under oxidation and annealing processes by combined x-ray reflectivity and x-ray absorption studies. We describe the progressive and inhomogeneous oxidation of the layers by increasing the oxidation time. Before annealing, the layers have lower density than bulk samples and noticeable roughness. After thermal annealing, a significant improvement of the quality of the alumina layer goes along with the formation of a CoPt alloy that reduces the number of Co-O bonds. These structural outcomes clarify the evolution of the magnetic and transport properties reported at room temperature in these samples

Influence of the pore diameter in Cu/Co/Cu antidots: A XANES study

“…The CoO thin layer spectrum was obtained from a Pt-Co and CoO-AlO x multilayer substrate reported in Ref. [48]. Additional Co bonding environments such as Pt-Co and Co-Al in the absorption signal of the CoO thin layer spectrum, which are not present in our samples, may explain the lower quality of fits compared to the CoO bulk spectrum.…”

“…We tested different reference spectra, including bulk Co metal, the unholed Co substrate, CoO bulk, CoO thin film (1.5 nm thickness from Ref. [48]), as well as Co 3 O 4 bulk. The two standard compounds that fit best the sample spectrum were evaluated from the χ 2 parameter, which is an indicator for the quality of the fit.…”

Temperature Variation of Magnetic Anisotropy inPt/Co/AlOxTrilayers

“…Underoxidized (shorter oxidation time) or overoxidized (longer oxidation time) interfaces exhibit weaker interfacial PMA (IPMA) at room temperature. It is also found that, upon annealing, oxygen tends to migrate to the Co=AlO x interface, thereby maximizing the interfacial PMA [15,16]. From an application point of view, this IPMA is very interesting in the context of STT MRAM since it allows obtaining out-of-plane magnetized magnetic tunnel junction with weak Gilbert damping and, therefore, low write current [12].…”

“…In this paper, low-temperature characterization of the anisotropy in Pt=Co=AlO x trilayers is performed and discussed in light of the previously investigated structural and chemical properties of these systems [16]. The samples of this study are the same as the ones measured in the previous studies [15,16].…”

“…In this paper, low-temperature characterization of the anisotropy in Pt=Co=AlO x trilayers is performed and discussed in light of the previously investigated structural and chemical properties of these systems [16]. The samples of this study are the same as the ones measured in the previous studies [15,16]. Specifically, we show that, besides the expected trends, the presence of CoO x and CoPt phases coming from, respectively, the oxidation and annealing process affects (i) the values of coercive (H C ) and anisotropy (H A ) fields at 4.2 K, (ii) the shapes of H C ðTÞ and H A ðTÞ curves between 300 and 4.2 K, and (iii) the onset of exchange bias at low temperature together with a large increase in coercivity in some cases of overoxidation of the Al layer.…”