M. Öztürk

Exchange bias properties of [Co/CoO]n multilayers

In this study, the exchange bias properties of four polycrystalline multilayer stack samples of antiferromagnetic (AF) CoO and ferromagnetic (FM) Co in the form of [CoO/Co]n with n = 1, 2, 3, and 5 are reported. The samples were grown on top of Si (001) substrates by using magnetron sputtering method. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were used to determine the structural properties of the samples. XPS measurements of cobalt oxide layer revealed the coexistence of different phases in cobalt oxide as CoO and Co3O4, the latter of which lowers the blocking temperature. The blocking temperature is also affected by the finite size scaling effects observed in AF layers. In-plane ferromagnetic resonance (FMR) measurements revealed uniaxial in-plane magnetic anisotropy for the samples. Low temperature vibrating sample magnetometer measurements provided exchange bias with a stepwise character. Observed steps are believed to be due to magnetization reversals of indivi...

Interface induced manipulation of perpendicular exchange bias in Pt/Co/(Pt,Cr)/CoO thin films

Perpendicular exchange bias has been manipulated by changing ferromagnetic film thickness and spacer layer in Pt/Co/(Pt,Cr)/CoO thin films. The exchange bias characteristics, blocking temperature, and magnetization of thin films strongly depend on the spacer layer (Pt,Cr) between ferromagnetic and antiferromagnetic layers. While Pt/Co/Pt/CoO thin films show perpendicular exchange bias, Pt/Co/Cr/CoO has exchange bias with easy magnetization axis in the film plane. We have also observed very small hysteretic behavior from the hard axis magnetization curve of Pt/Co/Cr/CoO film. This can be attributed to misalignment of the sample or small perpendicular contribution from Pt/Co bottom interface. We have also investigated the temperature and spacer layer dependent exchange bias properties of the samples. We observed higher HEB and HC for the thicker Co layer in the Pt/Co/Pt/CoO sample. In addition, onset of exchange bias effect starts at much lower temperatures for Pt/Co/Cr/CoO thin film. This clearly shows that Cr spacer layer not only removes the perpendicular exchange bias, but also reduces the exchange interaction between Co and CoO and thus lowers the TB.

Coexistence of perpendicular and in-plane exchange bias using a single ferromagnetic layer in Pt/Co/Cr/CoO thin film

We studied the temperature dependence of magnetization and exchange bias in a Pt/Co/Cr/CoO multilayer thin film. These magnetic multilayers are of particular interest since the easy axis of ultra-thin Co is strongly affected by the interfacial anisotropies of neighbouring Pt and Cr layers. The room temperature measurements show that the sample has a magnetic easy axis only in the film plane. However, upon cooling the sample, the easy axis of the magnetization departs from its initial orientation and typical easy-axis hysteresis loops are obtained for both in-plane and perpendicular directions. In accordance with this change in the magnetization direction at lower temperatures, the sample shows an unexpected coexistence of perpendicular and in-plane exchange bias below the antiferromagnetic transition of CoO. The temperature dependence of the exchange bias field for both directions is also significantly different. Along the film plane, the exchange bias field monotonically decreases and disappears at 220 K with increasing temperature. For the perpendicular direction, however, the exchange bias field increases and reaches a maximum value at 80 K. Then it decreases and disappears at 150 K with further increasing temperature. The mechanisms behind this anomalous temperature dependence of the exchange bias as well as the step-like behaviour in the hysteresis curves are discussed.

A Crystallographic, EPR and DFT Investigations of a Novel Magnetically Silent Mono-atom Acetate-Bridged Binuclear Schiff Base-Copper(II) Complex

Serkan Demir, Yusuf Yerli, Mustafa Öztürk, Hasan Saral, Ersin Temel, Serkan Başgel 1Department of Industrial Engineering, Faculty of Engineering, Giresun University, Giresun, Turkey. 2Yıldız Technical University, Science and Arts Faculty, Physics Department, İstanbul, Turkey. 3Gebze Institute of Technology, Faculty of Science, Department of Physics, Kocaeli, Turkey. 4Sinop University, Engineering Faculty, Metallurgical and Material Engineering, Sinop, Turkey. 5Department of Electricity and Energy, Vocational School of Technical Sciences, Giresun University, Giresun, Turkey. 6Laboratory Department, Middle Mediterranean Department of Customs and Trade, Ministry of Customs and Trade, Mersin, Turkey.