الملخص الإنجليزي
Nowadays, intensive studies have been devoted to the investigation of antiferromagnetic coupled (AFC) structures based on perpendicular magnetic anisotropy (PMA) materials for both fundamental research and technological applications. Although
the studies in such structures, it still needed to optimize the magnetic properties of these structures to use them in technological applications, especially, when reducing the size of the device to the nanoscale. Therefore, the aim of this research work is to fabricate and investigate AFC structures from soft (Co/Ni) and hard (Co/Pt) multilayers with PMA.
Then the interlayer exchange coupling strength Jex of the AFC structures is studied at a different range of temperatures. The twocandidates; (Co/Ni) and (Co/Pt) multilayers attracted enormous studies due to the possibility of tailoring their magnetic properties by
varying growth parameters. Particularly (Co/Ni) multilayers which consider as a promising candidate since they consist of both magnetic elements and hence possess high spin polarization and low damping constant.
In this work, (Co/Ni) multilayers with different repetition number N varied from 4 to 12 bilayers by a step of 2 have been investigated. The effect of the structure of magnetic multilayers on magnetic properties of fcc (111) (Co/Ni) multilayers has been
investigated by X-ray diffraction (XRD). XRD results reveal an increase in the intensity of (Co/Ni) multilayers peak as N increase which confirms the fcc (111) texture in as- deposited (Co/Ni) multilayers. However, a compressed strain induced by the seed Pt (111)
was observed which suggests a possibility of a magnetoelastic anisotropy contribution in PMA of (Co/Ni) multilayers. The magnetic properties were investigated experimentally by magnetic force microscopy (MFM) and Quantum Design physical property
measurement system (PPMS) and theoretically by a micromagnetic simulator known as oriented object micromagnetic framework (OOMMF). MFM results exhibit magnetostatic energy dominant by increasing N where the number of domains increases and the domain width decreases. The magnetostatic contribution can be seen in the shape of hysteresis loops measured by PPMS. As N increases a bow tie shape hysteresis loops can be observed and more obvious for 10 and 12 multilayers. The theoretical predictions by OOMMF simulation of the correlation between the saturation magnetization Ms and the anisotropy constant Ku are in contradiction with the experimental values obtained from the PPMS. The former predicts an inverse correlation between the values of Ms and Ku. However, the experimental values of Ku suggest an increase in both Ms and Ku values until N=8 and then drop for 10 and 12 multilayers. The influence of growth conditions and thermal fluctuations cannot be included in the micromagnetic simulation, for this reason, it shows different values for Ms and Ku. In this research, the structural and magnetic properties of the reference (Co/Pt) with 12 multilayers have been carried out by XRD and PPMS respectively. The out-of-plane hysteresis loops reveal a PMA of (Co/Pt) multilayers.
Building on the structural and magnetic properties of individual (Co/Ni) and (Co/Pt) multilayers, three samples of AFC structure are fabricated across Ru spacer with 0.8 nm thickness. In these AFC structure samples, the number of repeats N of (Co/Ni)
multilayers varied from 4 to 8 by a step of 2. The magnetic characterization of AFC structures is investigated at a temperature range of (25 K to 300 K).
[(Co/Ni)×4/Ru/(Co/Pt)×12] is the only sample that exhibits two distinct steps. On the other hand, no clear steps can be seen in AFC structure with 6 and 8 repeats of soft (Co/Ni). In [(Co/Ni)×4/Ru/(Co/Pt)×12], the interlayer exchange coupling Jex manifest a strong dependence on temperature with non-monotonous behavior. The maximum value of Jex is 0.13 erg/cm2 obtained at 150 K.
