Static and dynamic magnetic domain configurations in electrodeposited cobalt platinum nanowires. Muhammad Shahid Arshada, Kristina Žužek Rožmana, Matej Komelja, Paul J. McGuinessa, Spomenka Kobea,b aJozef
Stefan Institute, Department for Nanostructured Materials K7, Jamova Cesta 39 1000, Ljubljana, Slovenia. of excellence on nanoscience and nanotechnology (CENN Nanocenter), Jamova Cesta 39, 1000, Ljubljana, Slovenia.
bCenter
Hysteresis loop of a multidomain CoPt nanowire
INTRODUCTION The recent surge of interest in the magnetism of small elements stems from the following factors: 1. Deposition techniques like electrodeposition (ED) offers possibilities to fabricate nanosize magnetic materials and to manipulate the shape, size and geometry of the nanostructures. 2. Development of advanced magnetic characterization techniques such as magnetic force microscope (MFM) have become ever more sensitive with greater spatial resolution.
Au Sputtering
AAO
Pores Wall
Au on Bottom Side
Au
SEM Cross Sectional View
Flow w chart ffor three electrode electrodeposition of CoPt nanowires
400 nm
Bz~ 0 mT
Bz~-65mT
P5
Bz~ -95 mT
Hysteresis loop of an uniform/single domain CoPt nanowire M P3
(a) 1 μm
P4
(P5) Saturation state
Characterization (a) FEG-SEM micrograph showing cylindrical shape of CoPt single nanowire with length 5.5 μm and diameter 200 nm. (b) XRD showing the face-centered cubic (FCC) crystal structure of Co-Pt nanowires.
(P4) Coercivity state*
(P3) Remanence state
P3
AAO
Bz~ 90 mT
(P1) Quasiperiodic domain structure in a single isolated CoPt nanowire with length 5.5 μm and diameter 200 nm. (i) Nucleation state (ii) Collapse of dipoles at the two edges of the wire. (P2) Saturation state of wire
With this purpose in mind we synthesized soft ferromagnetic Co-Pt nanowires via electodeposition. Magnetic domain configurations of isolated Co-Pt nanowires with different lengths were investigated with magnetic force microscope (MFM).
AAO Membrane
Bz~ 70 mT
Bz~ 40 mT
P1
The happy confluence of these trends has created ideal conditions for fruitful and rapid exploration of magnetism in small magnetic structures such as nanowires, in particular, of their equilibrium (static) and dynamic magnetic domain structures, for device applications that fit in with the current trend of miniaturization in magneto-electronic technology.
ELECTRODEPOSITION (FABRICATION)
P2
(ii)
(i)
(ii)
(i)
(a)
P2
P2
P1
Length~5.5 μm
1 μm
200 nm
P1
H L=1μm
Bz~15mT
Bz~0mT
P4 P3
(a) AFM (Topology) of single isolated CoPt nanowires with length 1 μm and diameter 200 nm. (P1) MFM image of teh same nanowire without an external magnetic field. (P2) is the saturation magnetization state of the wire. (P3) remanence state of the wire. (P4) saturation state of the wire in the opposite field direction.
P4
(i) (ii) 1μm
(i) CoPt wire with length 1 μm and diameter 200 nm. (ii) nonmagnetic part of the membrane is attached (SEM)
Bz~-15mT
Bz~0mT
Two interacting nanowires under MFM
Co+2 Pt+2
(a) EDS analysis on nanowires have shown that they maintain composition of Co65±0.2Pt35±0.2
(b)
(c)
L R
MAGNETIC PROPERTIES Principle of MFM Bz~0mT
(b)
Bz~-40mT
(d)
(c)
(e) (e)
(a)
z y
Bz~-50mT
Bz~-80mT
Permanent magnet
x
(a) Artistic view on interaction between magnetic tip of MFM and magnetic stray field emanating from a single isolated nanowire with vortex domain structure. [1] (b) AFM/MFM-Veeco Dimension 3100 used for magnetic characterization (c) side view of apparatus arrangement with permanent magnet used to apply external magnetic field.
(d)
2 μm
(e)
Scan height 55nm Bz= 0mT
(a) AFM (Topology) of two CoPt nanowires with length 5.5 μm and diameter 200nm lying parallel to each other (b) the MFM image at 0mT (c) at -40mT an identical domain structure was observed in both nanowires (d) at -50mT “R” nanowire gets saturated and “L” nanowire vanishes (no zmagnetization) (e) while at -80mT reverse behavior was observed.
CONCLUSIONS We performed magnetic domain measurements with MFM on the electrodeposited Co65±2Pt35±2 nanowires with the lengths of 5.5 μm and 1 μm with the diameter of 200 nm. We applied the MFM imaging and observed domain patterns on the basis of the magnetization profile in nanowires lying horizontal on mica substrate. The response of the nanowire on the variation of the external magnetic field perpendicular to the nanowire principal axis was investigated. At zero applied field the MFM image for 5.5 μm nanowire exhibits a multiple domain structure with quasiperiodic domain configuration. With an increasing field, the experimental pattern becomes more uniform in the wire, due to alignment of the magnetic moments, mostly in the direction parallel to applied magnetic field. A further increase of the external-field magnitude yields a gradual reorientation of the moments starting from the lower middle part of the nanowire towards the extremities of the wire, which ends with the majority of the moments parallel to the field direction in the saturation state. In contrast, wire with length of 1 μm and diameter of 200 nm showed an uniform domain behavior. On application of the magnetic field all the magnetic moments reorient abruptly with an external magnetic field at small field without a domain movement. This process is characterized by the change in the contrast of the MFM image. Furthermore, because of the interaction between CoPt nanowires with length 5.5 μm and diameter 200 nm switching behavior was observed on application of the perpendicular field under MFM.
REFERENCES (d) AFM (e) MFM of Co-Pt single isolated nanowire with length 5.5 μm and diameter 200nm showing topology and domain structure. RESEARCH POSTER PRESENTATION DESIGN © 2012
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[1] T. Preisner, M. Greiff, U. B. Bala, W. Mathis, COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, (2009), 28, 120 - 129 Corresponding author: shahid.arshad@ijs.si