Co/Ni(111) superlattices studied by microscopy, x-ray absorption, andab initiocalculations

Abstract

We explore the origins of perpendicular magnetic anisotropy in epitaxial and textured Co/Ni (111) superlattices using a combination of thin film growth, structural characterization, x-ray magnetic circular dichroism (XMCD) and ab-initio calculations. Transmission electron microscopy and x-ray diffraction experiments allow us to show that the "bulk" magnetoelastic contribution to the total magnetic energy is small compared to the interface anisotropy. The magnetic properties are studied by using XMCD at the Co and Ni L 2,3 edges. Hysteresis loops performed at the Co L 3 edge confirm the perpendicular magnetization for Co thicknesses up to 4 monolayers. The spin and orbital moments were deduced using the XMCD sum rules. The results are explained by considering two kinds of magnetic moments for Co, distinguishing the interfaces from the rest of the layers. Both effective spin and orbital moments of Co atoms are found to be enhanced at the Co-Ni interfaces, whereas the magnetic moment of Co surrounded by Co is similar to the bulk values. Ab-initio calculations allow us to show a strong enhancement of the dipole operator contribution on Co atoms at the interface that is partly responsible for this high effective spin moment at the interface. Such a moment enhancement is not observed for Ni, the dipole operator contribution being close to zero. Finally, we observed a very surprising proportionality between the effective spin and orbital moments, independent of the absorption edge or deposition technique used. We assign this peculiar behavior to the fact that the magnetic dipole operator involved in the sum rules is closely linked to the increase of the Co orbital moment at the interface. Based on XMCD results obtained on both molecular beam epitaxy and sputter deposited samples, this link allows us to show the extreme sensitivity of the perpendicular anisotropy with the chemical ordering at the interface. 2

Promotion effect of nickel loaded on CdS for photocatalytic H 2 production in lactic acid solution

“…5b is the high-resolution XPS survey spectrum of the Ni peaks. The observed binding energy of Ni 2p 3/2 at 852.0 eV and 855.2 eV indicated the deposited nickel compounds on the surface of CdS contained metallic Ni and NiO [28,29], which was consistent with TEM results. The high-resolution XPS spectrum of Ni of the sample CNR was shown in Fig.…”

Effect of deposition technique of Ni on the perpendicular magnetic anisotropy in Co/Ni multilayers

“…Indeed, for both sample sets the roughness of the multilayered structures increases for increasing n. Therefore for our both sample sets, for decreasing trend of PMA with increasing n, the second explanation is valid. It was reported that MBE grown Co/Ni multilayers have a stronger PMA than sputtered Co/Ni multilayers due to more coherent growth [18,19]. However, there was no report about PMA of Co/Ni multilayers in which only the deposition method of Ni sublayers changed from sputtering to MBE.…”

“…Since H c ⊥ indicates the strength of PMA [22], the findings reveal that while even only Ni sub-layers are grown by MBE, a stronger PMA is obtained. The origin of PMA in Co/Ni multilayers is attributed to interface anisotropy in addition to bulk (111) magneto crystalline anisotropy [18]. Fig.…”

“…The deposition technique was also reported to be effective on magnetic properties of Co/Ni multilayered films [16,17]. For instance, if both of the Co and Ni layers were deposited by MBE instead of sputtering, stronger PMA was obtained [18,19]. However, to our knowledge, the effect of deposition method of Co or Ni single layers was not studied on magnetic anisotropy of Co/Ni multilayers.…”

State diagram of nanopillar spin valves with perpendicular magnetic anisotropy

“…To verify this point, an experimental study on an epitaxial crystalline [Co/Ni] system with a welldefinedanisotropy axis [95] K are also of great interest in magnetic recording media since higher thermal stability can be achieved [97,98] for a given reversal field. In the future it is then of great interest to continue the characterization and the study of the origin of perpendicular magnetic anisotropy in thin film and multilayers [99][100][101].…”