Resume of the research done until June 2013, and previous to a future paper. Evaluates the behavior of a Py nanostructure designed for trapping and detecting nanoparticles. The device has a switchable DW pinning site and it's state is probed measuring resistance variation due to anisotropic magnetoresistance effect. The presence of nanoparticles modifies the switching field.

1. Towards Space State of Domain Walls in
Permalloy Nanostructures
Héctor Corte1
*, Jonathan Fletcher1
, Patryk Krzysteczko2
, Hans Schumacher2
, and Olga Kazakova1
1
National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK.
2
Physikalisch-Technische Bundesanstalt, Braunschweig , D-38116, Germany
*hector.corte@npl.co.uk
3. Experimental Method1. Introduction
6. Bibliography
Electric transport measurements [4,5].
4 point resistance through the corner.
AC and DC current.
Magnetic field from –120 to +120 mT.
360º rotation of a sample with 1º step .
Current = 4 A.
Angles between 0º and 90º
Figure 4(a) black line:
A large negative field (1) creates a DW as the magneti-
sation in the device arms are tail to tail.
Reversing the field polarity first removes the DW (2),
seen as an increase in resistance (3).
Eventually a DW of the reverse polarity is found (4) and
the resistance decreases again.
Red line: This process can be reversed to recover the ini-
tial state (5-8).
Angles between 90º and 180º
Figure 4(b) black line.
In this orientation a large negative field (1) creates a tail
to head configuration with no DW.
Reversing the field polarity (2), nucleates a DW, seen as
a decrease in resistance (3).
Eventually the DW is removed and the resistance raises
again (4).
Red line: The process can be inverted to recover the ini-
tial state (5-8).
Angular dependence.
Figure 4(c). Resistance behaviour in respect to the mag-
netic field and angles between 0º and 180º.
Nucleation and propagation fields, and magnetoresis-
tive background, are angular dependant.
There is an asymmetry between the two types of AMR
hysteresis loops, occurring at 0< <90º and 90º< <180º.
Abrupt change in behaviour at 90º.
[1] T.R. McGuire, R. I. Potter, IEEE Trans. Mag, vol. MAG-11, No. 4, July
1975.
[2] J-E Wegrowe, D. Kelly, A. Franck, S.E. Gilbert, and J.-Ph. Ansermet, Phys.
Rev. Lett. 82, 3681–3684 (1999).
[3] A.B. Oliveira, S.M. Rezende, A. Azevedo, Phys. Rev. B, 78, 024423 (2008).
[4] M. Donolato, M. Gobbi, P. Vavassori et al. Nanotechnology 20 (2009)
385501.
[5] D.A. Allwood, N. Vernier, Gang Xiong, M.D. Cooke, D. Atkinson et al.
Appl. Phys. Lett. 81, 4005 (2002).
[6] D.A. Allwood et al. Science 309, 1688 (2005).
Follow link to download:
http://www.npl.co.uk/publications/science-posters/towards-
space-state-of-domain-walls-in-permalloy-nanostrutures
2. Device
Figure 1. SEM image of the L-shaped device.
Ferromagnetic materials exhibit a number
of magnetoresistive effects [1], one of
which is Anisotropic Magneto Resistance
(AMR).
In AMR, an applied magnetic field chang-
es the magnetization of the material and
forces the spins to align, modifying the
conductivity of the material through a spin
-orbit interaction [1,2,3].
AMR can be used to detect the presence or
absence of a Domain Wall (DW) in a ma-
terial through a variation in the resistance
[3,4,5].
Here we use AMR to study a L-shape de-
vice [4,5], which was designed for trap-
ping a DW in the corner. The presence of
the DW tends to lower the resistance and,
since the magnetic field needed for remov-
ing the DW can be tuned through the
width of the device [3,4,5], one can use
these devices for magnetosensing applica-
tions, for example, detecting the presence
of a nanoparticle [4] or as a part of a mag-
netic logic setup [6].
5. Conclusion
Steps on the AMR major loops corresponds to sequen-
tial switching of the magnetization in both arms of the
device.
Within two main angular ranges (0< <90º and 90º<
<180º) nucleation and propagation fields change gradu-
ally. At the same time, a threshold behaviour between
two types of curves has been measured at =90º.
Angular AMR measurements can be used to track the
state of the device as well as the events corresponding
to nucleation and propagation of DW.
Figure 2. MFM images of stable states at zero field after applying a field indicated by arrows.
4. AMR as a function of field angle
Figure 3. Experimental setup for magneto-transport meas-
urements with angular and magnetic field dependence.
Figure 4. Typical AMR as a function of field for (a) 0<q<90º , (b) 90º<q<180º. (c) Mapping of AMR, versus angle, q, and field, H.
(a) (b)Magnetization states. Magnetization states.
(c)
L-Shape nanostructure of
Permalloy:
SiO substrate.
Au contacts.
Disks reduce stray field.
Designs with different
widths tested.
4 zero field states.