94 research outputs found
MR head response from arrays of lithographically patterned perpendicular nickel columns
Effects of boundary conditions on magnetization switching in kinetic Ising models of nanoscale ferromagnets
Magnetization switching in highly anisotropic single-domain ferromagnets has
been previously shown to be qualitatively described by the droplet theory of
metastable decay and simulations of two-dimensional kinetic Ising systems with
periodic boundary conditions. In this article we consider the effects of
boundary conditions on the switching phenomena. A rich range of behaviors is
predicted by droplet theory: the specific mechanism by which switching occurs
depends on the structure of the boundary, the particle size, the temperature,
and the strength of the applied field. The theory predicts the existence of a
peak in the switching field as a function of system size in both systems with
periodic boundary conditions and in systems with boundaries. The size of the
peak is strongly dependent on the boundary effects. It is generally reduced by
open boundary conditions, and in some cases it disappears if the boundaries are
too favorable towards nucleation. However, we also demonstrate conditions under
which the peak remains discernible. This peak arises as a purely dynamic effect
and is not related to the possible existence of multiple domains. We illustrate
the predictions of droplet theory by Monte Carlo simulations of two-dimensional
Ising systems with various system shapes and boundary conditions.Comment: RevTex, 48 pages, 13 figure
Portaria 116/CSE/2017 - Torna pública a composição da banca examinadora para o concurso público, Processo nº 23080.030439/2017-76
We report, for the first time, the MR head response from lithographically patterned perpendicular nickel columns. Electron-beam lithography is used to fabricate arrays of Ni columns, 400 nm tall and 150 nm in diameter spaced 2.1 μm apart, embedded in SiO2. The sample surface is planarized with a chemical mechanical polish. The technique of Scanning Magnetoresistance Microscopy (SMRM), in which a magnetoresistive (MR) head is raster-scanned in contact with a sample, is used to investigate the MR head response from the Ni columns. Single columns can be “read” with a 0-peak MR voltage of 60-70 μV. Unexpectedly, we find that the magnetic field due to the bias current in the MR head is enough to switch the columns during scanning, which results in a “dibit-like” MR response, By scanning in the presence of a small (~21 Oe) external magnetic bias field, the columns can be imaged in either their “up” or “down” magnetic states
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