arXiv subjects

Justin M. Shaw

Publications and source records attributed to Justin M. Shaw.

39 records · Page 3Linked to original sources

arXiv2013

Measurement of orbital asymmetry and strain in Co90Fe10/Ni multilayers and alloys: Origins of perpendicular anisotropy

We use broadband ferromagnetic resonance spectroscopy and x-ray diffraction to investigate the fundamental origin of perpendicular anisotropy in Co90Fe10/Ni multilayers. By careful evaluation of the spectroscopic g-factor, we determine the orbital moment along the out-of-plane and in-plane directions. For the multilayers, we find a direct relationship between the orbital moment asymmetry and the perpendicular anisotropy, consistent with the theory of Bruno [P.Bruno, Phys. Rev. B, 39, 865 (1989)]. A systematic x-ray diffraction study revealed the presence of a trigonal strain as high as 0.7 % in some samples. However, we found no direct correlation between the strain and the anisotropy, indicating that the anisotropy is not dominated by magnetoelastic effects. In order to further study the interface structure on the anisotropy, we prepared a set of equivalent alloy samples. The strain in the alloy samples was comparable to that of the multilayer samples; however the orbital moment asymmetry in the alloy samples showed a very different trend allowing us to isolate the effect of the interfaces in the multilayers.

cond-mat.mtrl-sci↗

arXiv2012

Epitaxial (111) Films of Cu, Ni, and Cu$_xNi$_y$ on α-Al$_2$O$_3$(0001) for Graphene Growth by Chemical Vapor Deposition

Films of (111)-textured Cu, Ni, and Cu$_x$Ni$_y$ were evaluated as substrates for chemical vapor deposition of graphene. A metal thickness of 400 nm to 700 nm was sputtered onto a substrate of $α-$Al$_2$O$_3$(0001) at temperatures of 250 C to 650 C. The films were then annealed at 1000 C in a tube furnace. X-ray and electron backscatter diffraction measurements showed all films have (111) texture but have grains with in-plane orientations differing by $60^{\circ}$. The in-plane epitaxial relationship for all films was $[110]_{metal}$||$[10\bar{1}0]_{{Al}_{2}{O}_{3}}$. Reactive sputtering of Al in O$_2$ before metal deposition resulted in a single in-plane orientation over 97 % of the Ni film but had no significant effect on the Cu grain structure. Transmission electron microscopy showed a clean Ni/Al$_2$O$_3$ interface, confirmed the epitaxial relationship, and showed that formation of the $60^{\circ}$ twin grains was associated with features on the Al$_2$O$_3$ surface. Increasing total pressure and Cu vapor pressure during annealing decreased the roughness of Cu and and Cu$_x$Ni$_y$ films. Graphene grown on the Ni(111) films was more uniform than that grown on polycrystalline Ni/SiO$_2$ films, but still showed thickness variations on a much smaller length scale than the distance between grains.

cond-mat.mtrl-sci↗

arXiv2009

Spin Transfer Dynamics in Spin Valves with Out-of-plane Magnetized CoNi Free Layers

We have measured spin transfer-induced dynamics in magnetic nanocontact devices having a perpendicularly magnetized Co/Ni free layer and an in-plane magnetized CoFe fixed layer. The frequencies and powers of the excitations agree well with the predictions of the single-domain model and indicate that the excited dynamics correspond to precessional orbits with angles ranging from zero to 90 degrees as the applied current is increased at a fixed field. From measurements of the onset current as a function of applied field strength we estimate the magnitude of the spin torque asymmetry parameter lambda ~ 1.5. By combining these with spin torque ferromagnetic resonance measurements, we also estimate the spin wave radiation loss in these devices.

cond-mat.mes-hall↗