Weakly coupled synthetic antiferromagnetic nanodisks with perpendicular magnetic anisotropy for lab-on-chip devices

Synthetic antiferromagnetic particles with perpendicular magnetic anisotropy offer a highly desirable platform for use in fluidic applications. This work illustrates their high level of switching field tunability and demonstrates the ability to use particle design to overcome unfavorable hysteretic changes during patterning to manufacture functional, low switching field nanodisks. This makes them ideal candidates for lab-on-chip technologies such as microfluidic sorting or detection devices.Rosetrees Trus

Vertical shift register using dipolar interaction in magnetic multilayers

A vertical shift register consisting of multi-layered ferromagnetic bars with in-plane magnetization is investigated numerically using macrospin simulations. These layers are anti-ferromagnetically coupled via dipolar interactions and their in-plane aspect ratio determines their anisotropy. A single data bit is represented by a magnetic kink soliton, which forms at the boundary of two anti-parallel domains with opposite phases. It can be propagated bi-directionally using an externally applied rotating magnetic field. The soliton propagation is dependent on the applied field strength, the magnetic anisotropy of the ferromagnetic layers, and the dipolar coupling energies. For the device investigated here, the largest field range for soliton propagation is found to be from 35 Oe to 235 Oe at a lateral aspect ratio of 1.33. The soliton is also subjected to edge effects where it can be either pinned or reflected rather than being expelled from the stack. It is found that by reducing the thickness of the edge layer, these effects can be reduced substantially. By reducing the thickness of the edge layer by 20%, the field range in which the soliton is expelled increases by more than a factor of two.This project has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 309589 (M3d), as well as the Seventh Framework Programme ERC Contract No. 247368 (3SPIN). AFP acknowledges funding from an EPSRC Early Career Fellowship, EP/M008517/1 and from the Winton Foundation.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.493791

Controlling domain wall nucleation and injection through focussed ion beam irradiation in perpendicularly magnetized nanowires

Using Ga$^{+}$ focussed ion beam irradiation of Ta/Pt/CoFeB/Pt perpendicularly magnetized nanowires, the nucleation and injection fields of domain walls into the nanowires is controlled. The nucleation and injection fields can be varied as a function of dose, however, the range of injection fields is found to be limited by the creation of a step in anisotropy between the irradiated and unirradiated regions. This can be altered by defocussing the beam, which allows the injection fields to be further reduced. The ability to define an arbitrary dose profile allows domain walls to be injected at different fields either side of an asymmetrically irradiated area, which could form the initial stage of a logic device. The effect of the thickness of the magnetic layer and the thickness of a Ta underlayer on the dose required to remove the perpendicular anisotropy is also studied and is seen that for similar Ta underlayers the dose is determined by the thickness of the magnetic layer rather than its anisotropy. This finding is supported by some transport of ions in matter simulations.This research was funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN, and by EMRP JRP EXL04 SpinCal. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the EU. AB acknowledges DTA funding from the EPSRC

The effect of underlayers on the reversal of perpendicularly magnetized multilayer thin films for magnetic micro- and nanoparticles

Perpendicularly magnetized microparticles offer the ability to locally apply high torques on soft matter under an applied magnetic field. These particles are engineered to have a zero remanence magnetic configuration via synthetic antiferromagnetic coupling using a Ru coupling interlayer. The flexibility offered by the top down thin film fabrication process in a CoFeB/Pt perpendicular thin film is demonstrated by using the Pt interlayer thicknesses in a Pt/Ru/Pt antiferromagnetic coupling multilayer to tune the applied magnetic field value of the easy axis spin-flip transition to saturation and hence the field value at which the magnetic particles are magnetically activated via a distinct transition to saturation. The importance of a Ta buffer layer on the magnetic behavior of the stack is shown. While Au capping layers are desirable for biotechnology applications, we demonstrate that they can drastically change the nucleation and propagation of domains in the film, thereby altering the reversal behavior of the thin film. The effect of Au underlayers on a multilayer thin film composed of repeated motifs of a synthetic antiferromagnetic building block is also investigated.</jats:p

A robust soliton ratchet using combined antiferromagnetic and ferromagnetic interlayer couplings

A sharp magnetic soliton can be created and propagated in a vertical ratchet structure based on magnetic layers with out-of-plane anisotropy using a combination of antiferromagnetic and ferromagnetic interlayer couplings. This allows the use of identical magnetic layers in the stack, which simplifies the implementation of the ratchet compared to schemes which use alternating layer thicknesses. The ratchet behavior is analyzed using an Ising-macrospin approximation and conditions are derived for the propagation of a soliton, which is demonstrated experimentally. Values extracted from the experimental data for the coercivities and interlayer couplings show significant variation, which demonstrates the robustness of the soliton propagation.This research was funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN. R.L. acknowledges support from the Netherlands Organization for Scientific Research (VENI 68047428). A.F.-P. acknowledges an EPSRC Early Career fellowship and support from the Winton Programme for the Physics of Sustainability.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.491401

Research data supporting "The mechanical response in a fluid of synthetic antiferromagnetic and ferrimagnetic microdiscs with perpendicular magnetic anisotropy"

This dataset is the magnetometry data for the publication listed above with Applied Physics Letters

Controllable nucleation and propagation of topological magnetic solitons in CoFeB/Ru ferrimagnetic superlattices

We control the nucleation and propagation of topological magnetic solitons in synthetic ferrimagnetic (CoFeB/Ru) N superlattices (N = 6). This is achieved by carefully tuning the anisotropy and thickness of one of the edge layers, making it different from the other layers of the superlattice. Sharp solitons can be nucleated at one edge of the system, then unidirectionally propagated using external magnetic fields. Experimental results are modeled with macrospin simulations. We present a numerical phase diagram which maps the general behavior for the nucleation and propagation of solitons in ferrimagnets

Supporting data for 'Sputter grown Fe and Fe/Cr multilayers with four-fold magnetic anisotropy on GaAs'

Supporting data for the paper 'Sputter grown Fe and Fe/Cr multilayers with four-fold magnetic anisotropy on GaAs' published in IEEE Transactions on Magnetics.ERC (ERC: 247368); Netherlands Organization for Scientific Research (NWO) (NWO-Rubicon 680-50-1024