Magnetoresistance of oblique angle deposited multilayered Co/Cu nanocolumns measured by a scanning tunnelling microscope

Abstract

In this work we present the first magnetoresistance measurements on multilayered vertical Co(∼6 nm)/Cu(∼6 nm) and slanted Co(x nm)/Cu(x nm) (with x≈6, 11, and 16 nm) nanocolumns grown by oblique angle vapour deposition. The measurements are performed at room temperature on the as-deposited nanocolumn samples using a scanning tunnelling microscope to establish electronic contact with a small number of nanocolumns while an electromagnet generates a time varying (0.1 Hz) magnetic field in the plane of the substrate. The samples show a giant magnetoresistance (GMR) response ranging from 0.2 to 2%, with the higher GMR values observed for the thinner layers. For the slanted nanocolumns, we observed anisotropy in the GMR with respect to the relative orientation (parallel or perpendicular) between the incident vapour flux and the magnetic field applied in the substrate plane. We explain the anisotropy by noting that the column axis is the magnetic easy axis, so the magnetization reversal occurs more easily when the magnetic field is applied along the incident flux direction (i.e., nearly along the column axis) than when the field is applied perpendicular to the incident flux direction.

Large-Area Nanopillar Arrays by Glancing Angle Deposition with Tailored Magnetic Properties

“…So, the first step of the loop corresponds to the magnetization switching from the positive direction to the vertical one, whereas the second step is the switching from the vertical direction to the negative direction. It is worth mentioning that this kind of hysteresis loop with two steps when the field is applied along the direction has been also reported by Morrow et al [ 24 ] and by Wang et al [ 18 ].…”

“…This effective uniaxial magnetic anisotropy has been reported in other works. With samples fabricated by thermal evaporation, Bubbendorf et al found it in obliquely deposited Fe films [ 22 ] and Morrow et al also described it in Co/Cu multilayered slanted nanopillars [ 24 ]. In the case of sputtering, Schlage et al observed similar behavior in 5 nm thick polycrystalline iron films prepared with 80° tilt angle [ 25 ] and Wang et al reported analogous anisotropy in permalloy films obliquely deposited at 50° [ 18 ].…”

“…In the case of magnetic materials, although oblique deposition had already been used in the past to control the magnetic anisotropy of thin films [ 9 , 10 , 11 , 12 , 13 ], the GLAD configuration (i.e., tilt angle beyond 70°) was firstly serving to produce nanostructure arrays at the end of the 20th century [ 14 , 15 ]. Since then, different properties of the magnetic films obtained by GLAD have been studied: the magnetic domain structure [ 16 , 17 , 18 , 19 ], the magnetic anisotropy [ 20 , 21 , 22 , 23 ], the magneto-resistance [ 24 , 25 , 26 ], the optical and magneto-optical behaviors [ 27 , 28 ], and even their possible use for information storage [ 29 , 30 , 31 ]. Nevertheless, only a few of those studies refer to arrays fabricated by MS-GLAD [ 19 , 25 , 31 , 32 , 33 ].…”

Ferromagnetic Multilayers: Magnetoresistance, Magnetic Anisotropy, and Beyond

“…The Oblique incidence e-beam evaporation technique is one of the preferred methods for controlling magnetic properties of micro to nano-sized multilayered films. Recent work on FM multilayers have shown that obliquely deposited multilayers exhibit strong magnetic anisotropy and the magnitude of the anisotropy enhances when samples are annealed in the presence of H field [4,19,[92][93][94]. Since these multilayers are deposited onto the substrate by changing deposition angle, this technique help break structural symmetry with respect to multilayer plane, producing tilted columns, shadowing effects and voids in the directions parallel to the plane of evaporation: The deposited particles can also form chains of crystallites, leaving behind some voids, and these voids lead to an array of fine crystals that extend in the direction perpendicular to the direction of the incidence beam [20,24,30,95].…”

“…Ferromagnetic (FM) multilayered films are important materials because they exhibit interesting physical properties such as giant magnetoresistance (GMR) [1][2][3][4][5][6], magnetic anisotropy (MA) [7][8][9], tunneling magnetoresistance (TMR) [10], surface plasmon-resonance (SPR) and giant magneto-reflectivity (GMRE) [11][12][13][14]. These properties are very sensitive to the microstructure of the multilayered film.…”