Domain well motion in permalloy wires

Magnetic domain wall motion in permalloy wires with nanometer-scaled notches

Introduction

The dynamics of domain wall motion in ferromagnetic nanowire (NW) is of crucial importance from the view of  fundamental research as well as in advancement of future technology such as magnetic memory and logic devices.

These dynamics can be driven by the application of magnetic field or by flowing the current using novel physics of spin transfer torque.

It is necessary to control the motion of a domain wall along the nanowire to realize the practical application of domain wall based devices. Several efforts have been made  to  engineer the domain wall motion  in magnetic nanowire  by  inclusion of artificial constraints in the nanowire.

In this work, artificial constraint such as ‘notch’ of different depth has  been fabricated  in the permalloy nanowire using  electron -beam lithography and lift-off method. Magnetic field induced effect in nanowires having different notch depth has been investigated by an in-situ MFM measurements.


MFM images of 127nm depth notched wires

domain-well-motion-in-permalloy-wires01

L= 12μm, W= 300nm, thickness= 25nm

In-situ MFM images taken under different field have shown that magnetization switching took place singly in each Nanowire.

The squared area (A) reveals an anti-parallel configuration which suggests that the interaction forces between neighboring wires affect the reversal behavior.

The switching field is found to be ~24 Oe.


MFM images of 171nm depth notched wires

domain-well-motion-in-permalloy-wires02

L= 12μm, W= 300nm, thickness= 25nm

In this configuration, the magnetization reversal has taken place differently in each wire under the applied fields.

Squared area‘B’shows that the two consecutive wires are parallel  and the other one is antiparallel, whereas‘A’shows antiparallel nature.

The switching field is found to be ~21 Oe.


MFM images of 143nm depth notched dumbbell wires

domain-well-motion-in-permalloy-wires03

L= 12μm,W= 300nm,D= 1.5μm,thickness= 25nm

The dark (or bright) contrast in a disk suggest the domain wall nucleation  in dumbbell-shape pad easier, as shown in blue boxes.

Green box shows the emergence of domain wall from the disk and this is captured at the constructed notch in the nanowire.

The structure shown in red box is more complex domain structure that will be tested further.

The switching field is found to be ~44 Oe.