Structural, microstructural and magnetic domain configurations in multisegmented electrodeposited CoPt nanostructures Muhammad Shahid Arshada, Kristina Žužek Rožmana, Saso Sturma, Janez Zavasnika, Matej Komelja, Paul J. McGuinessa, Spomenka Kobea,b aJozef bCenter
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.
MAGNETIC PROPERTIES
INTRODUCTION Principle of MFM
Metal ferromagnetic nanostructures are of great interest as materials for future magnetic memory devices, biomedical sensors, and spin controlled devices due their unique magnetic properties as a result of their low dimensionality. [1-2] Increasing demand of nanostructures in many applications make desirable for single nanostructure to perform multifunctions simultaneously. One way to achieve this manifesto is to build nanostructures from two or more components to integrate multifunctionality. In recent years, multisegmented magnetic nanostructures have gain huge attention due to their obvious multipurpose use in applications and also to understand their fundamental physics such as magnetization reversal. [3] Recently, it has been demonstrated that the use of multisegmented nanotubes could help to stabilize the magnetic nanoparticles inside ferromagnetic nanotubes.[4] For biomedical applications nanotubes could suffer detection problem due to low magnetic signature, however nanowires could resolve this issue.[3] Following these ideas, in this work we have investigated multisegmented cylindrical CoPt nanorods with alternating magnetic tube and wire segments. We focused on microstructure and magnetic domain dynamics of the nanorods.
(b)
(a)
z Permanent magnet
x
y
(a) Artistic view on interaction between magnetic tip of MFM and magnetic stray field emanating from a single nanostructure. (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.
(e)
(d)
Characterization
ELECTRODEPOSITION (FABRICATION)
Au Sputtering
AAO
Pores Wall
Au on Bottom Side
(a)
2 μm
1 μm
Length~4.6 μm
260 nm (d) AFM (e) MFM of Co-Pt single isolated nanostructure with length 4.6 μm and diameter around 250nm showing topology and domain structure at scan height of 60nm. 300 nm
250 nm
Hysteresis loop of a multidomain CoPt nanostructure 1 μm
Au
SEM on AAO Membrane
TEM of single CoPt nanorod (a) 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
1 μm (c)
(b)
(d)
(a) TEM image of a CoPt nanorod with length 5.76 μm (e) and diameter ~250nm. (b) SAED pattern was taken at nanotube part. The lattice parameter calculated from ring pattern was 3.74 Å which corresponds to CoPt FCC. Inset: randomly distributed grains. 10 nm (c) SAED pattern was taken at nanowire segment. Inset: o grains are arranged with mismatch around ±15 . Analysis have shown that the orientation is in <111> crystal direction. Explanation: As the nanorod grow the CoPt crystallites start to align themselves due to (e) HRTEM image taken at the transparent confined geometry of the membrane. part of the nanorod. Grain size 5-10nm (d) Composition between Co and Pt along the length of the nanorod. Inset: HAADF image of the same nanorod. RESEARCH POSTER PRESENTATION DESIGN © 2012
www.PosterPresentations.com
Remanence state
1 μm
Corresponding author: shahid.arshad@ijs.si
This PhD project was supported by ARRS funding of Republic of Slovenia under project number PR-04442.
AAO 300 nm
MFM
AFM
(a) FEG-SEM micrograph showing cylindrical shape of CoPt single nanowire with length 4.6 μm and diameter ~250 nm. EDS line analysis on an isolated nanostructure revealed composition of Co65±2Pt35±2 (b) XRD showing the face-centered cubic (FCC) crystal structure of Co-Pt nanostructures.
Three electrode electrodeposition of CoPt nanostructures
AAO Membrane
(c)
(1)
(3)
(2)
Bz~ 0 mT
Bz~ 0 mT
Bz ~15mT
(1) (2) Quasiperiodic domain structure in a single isolated CoPt nanostructure with length 4.6 μm and diameter 200 nm, domain width is ~130-250 nm and domain wall thickness ~25-32 nm. red encircle region is nanotube section. (3) and (4) domain expansion at 15mT and 35mT (5) Saturation state (6) Remanence state of the wire
(5)
(4)
Bz ~35mT
(6)
Bz ~65mT
Rem state
CONCLUSIONS In this work we have investigated multisegmented cylindrical CoPt nanorods with alternating magnetic tube and wire segments. In TEM we found that the nanorod consists on 1 μm long nanotube and rest nanowire section. Moreover, nanotube section was found consist on randomly distributed grains with size of 5-10nm. In contrast, in nanowire section grains start to orient in <111> crystal direction. We have applied the MFM imaging and observed domain patterns on the basis of the magnetization profile in nanostructures lying horizontal on Si substrate. The response of the nanostructure on the variation of the external magnetic field perpendicular to the nanostructure principal axis was investigated. At zero applied field the MFM image for 4.6 μm nanostructure exhibits a multiple domain structure with quasiperiodic domain configuration. The periodic domain structure is a result of competition between shape anisotropy and magnetocrystalline anistropy. [5] 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 and expansion of magnetic domains already in the direction of applied field, Which ends with the majority of the moments parallel to the field direction in the saturation state.
REFERENCES [1] Bader, S. D., Colloquium: Opportunities in nanomagnetism, Review of Modern Physics, 78, 15, 2006., [2] Cowburn, R. P., Property variation with shape in magnetic nanoelements, Journal of magnetism and magnetic materials, 505, 4, 2002., [3] Hurst, S. J.; Payne, E. K.; Qin, L. and Mirkin, C. A., Multisegmented One-Dimensional Nanorods Prepared by Hard-Template Synthetic Methods, Angewandte Chemie International Edition, 45, 2672-2692, 2006., [4] Neumann, R. F., et al., Confinement of magnetic nanoparticles inside multisegmented nanotubes by means of magnetic field gradients, Journal of Applied Physics, 111, 013916-6, 2012. [5] Gerd Bergmann; Jia G. Lu; Yaqi Tao and Thompson, a. R. S., Frustrated Magnetization in Co nanowires: Competition between crystal anisotropy and demagnetization energy, Physical Review B, 77, 5, 2008.