Thickness dependence of the total magnetic moment per atom in the Cu/Ni/Cu/Si(001) system

Abstract

Systematic measurements of the magnetic moment per Ni atom in Cu/Ni/Cu/Si͑001͒ structures have been made using polarized neutron reflection ͑PNR͒ for Ni thicknesses in the range 30 ÅϽtϽ400 Å at room temperature. We find a dramatic reduction in the magnetic moment per atom for tϽ100 Å and near bulk values above 100 Å. These results are corroborated by alternating gradient magnetometer measurements on the same samples. A Cu/Ni-wedge/Cu/Si͑001͒ structure with 30 ÅϽtϽ150 Å was studied using magnetic circular x-ray dichroism ͑MCXD͒, polar magneto-optical Kerr effect ͑MOKE͒, and reflection high-energy electron diffraction ͑RHEED͒ in order to estimate the variation in the values of ͗L z ͘, ͗S z ͘, perpendicular anisotropy strength, and surface in-plane Ni lattice constant, respectively, during epitaxial growth. RHEED measurements show that the in-plane lattice constant falls by 1.7% in the Ni thickness range 30 ÅϽtϽ90 Å. The MCXD measurements reveal the same trend for ͗L z ͘, ͗S z ͘, and total moment per atom versus Ni thickness as found for the total moment by PNR. Polar MOKE measurements confirmed the transition from a perpendicular easy axis towards an in-plane magnetic easy axis as has already been extensively studied in the literature. Comparison of the PNR results with RHEED measurements reveal a striking correlation between the increase of in-plane strain and reduction in magnetic moment per atom with decreasing Ni thickness. While a direct strain-induced variation of the moment based on bulk phase calculations cannot account for the magnitude of the moment variations we observe, we show that the results cannot be attributed to sample contamination, interdiffusion, or a reduction of the Curie temperature with decreasing Ni thickness. Furthermore, the presence of a magnetically dead layer in the samples is not consistent with the PNR results. The strong moment variation partially explains the large thickness range for which perpendicular anisotropy is observed in this system.

Electronic structure studies of the buried Ni layer in a Cu/Ni/Cu multilayer by resonant photoemission at the Ni L3 edge

“…11 The present multilayer system with the 50 Å thick buried Ni layer has been reported to show magnetization parallel to the layer. 9,12 This is confirmed by the MOKE measurements shown in the inset of Fig. 1.…”

“…Among the variety of magnetic multilayer systems, the Ni on Cu system is a well-studied system that shows various magnetic properties depending on the thickness of the Ni and Cu surfaces. 9 Having a Cu cap layer on the Ni layer presents a more realistic system that is used in industry.…”

Phase formation, thermal stability and magnetic moment of cobalt nitride thin films

“…Neutrons interact with the magnetic field generated by unpaired spins on an atomic magnet via dipolar interaction. The magnetic potential for such kind of interaction is given by 40 V m = −µ n · B. Where magnetic induction B = H + 4πM, µ n is neutron magnetic moment and M is sample magnetization.…”

A new polarized neutron reflectometer at Dhruva for specular and off-specular neutron reflectivity studies

“…Also the Ni layers at the interfaces have considerably lower moment compared to the Ni in the bulk layer. Such reduction in magnetic moment of Ni atom in Cu/Ni/Cu/Si(001) system had also been observed by Hope et al [15]. To fit the PNR data, we needed to add a magnetic moment of 0.10±0.02m B per Cu atom at the interface Cu layers i.e.…”