research line, from the synthesis of hybrid materials to the final analysis. Laser and sputter deposition systems are used to grow thin films, typically between one and 100 nanometres thick. Lithography is then used to pattern continuous multilayer films into nanoscale structures for the characterisation of various functional properties such as electronic transport, magnetic switching and spin wave emission and propagation. “Individually, our components are
actually quite conventional, in terms of their composition. The ‘building blocks’ are derived from fairly standard materials,” says van Dijken. “For example, for ferromagnetic films we’ve used cobalt, iron and nickel, and for the ferroelectric counterparts we have used barium titanate and lead titanate. The essential novelty of our project lies in combining these types of material in a utilitarian way, to harness their discrete properties and to create new functions.”
By employing hybrid multiferroic
materials, however, electric fields can be used to control magnetic devices, nullifying these drawbacks, according to van Dijken. “Because they can be integrated in small scale electrical devices, components which utilise electric fields could thus become very advantageous in many contexts,” he asserts. Since the design needed is fairly basic – a ferroelectric layer sandwiched between two metallic electrodes, to which a bias voltage is applied – it is readily scaleable. Ferroelectric materials are insulators, and so the application of an electric field will not
result thus limiting the power
in a significant current flow, usage
introducing significant economies to the system. Magnetic sensors,
and commonly
found in cars, are another area in which new functionalities could be realised using multiferroic hybrids, as are logic operations in computing. The emission of microwaves could also be
controlled and tuned by multiferroics. “Some high frequency
“The essential novelty of our project lies in combining ferroelectric and ferromagnetic materials in a utilitarian way, to harness their discrete properties and to create new functions”
Achieving control over these hybrid
materials is a highly desirable objective. Many mainstream technologies depend on the principle of manipulating the direction of magnetic order. For example, computer hard disk drives ‘write’ information magnetically, by realigning small sections of the drive to represent either a binary 1 or a 0. The way most information is stored relies on the application of magnetic fields. New types of memory are being developed, such as non-volatile magnetic RAM (MRAM) memory, which use an electric current to write information. However, there are disadvantages to both of these mechanisms. Electromagnets are bulky components that make storage optimisation difficult, while manipulating data using an electric current uses large amounts of energy.
www.projectsmagazine.eu.com electronic
components are based on the principle of ferromagnetic resonance, and hence they could find great utility here,” says van Dijken. “This is a current research theme for us. We’re examining how our materials respond at high frequency and how to manipulate ferromagnetic resonance effects using a bias voltage. Once mastered, the technique could aid the creation of new, tuneable microwave devices or components. Presently, wireless products like mobile phones operate using fixed frequencies, but, by using these new materials, tuneable models capable of accessing different frequencies could be delivered.” To date, the project has already delivered
a robust coupling system, which augurs well for its future explorations. “Both classes of materials we’re using are subdivided – split into different domains in which magnetisation or polarisation point in different directions,” explains van Dijken. “Normally, the material isn’t uniform in this respect. However, through coupling them, the ferroelectric domains can be powerfully imprinted into the ferromagnetic film. Because of this, the magnetic orientation and the ferroelectric polarisation of the hybrid become mutually aligned throughout. This emphasises the strength of the bond we’ve achieved between the two materials. It’s highly encouraging, and creates a variety of new opportunities for future research and practical development within our group.”
★ 29
AT A GLANCE Project Information
Project Title: Electric-Field Control of Magnetic Domain Wall Dynamics and Fast Magnetic Switching: Magnetoelectrics at Micro, Nano, and Atomic Length Scales (E-CONTROL)
Project Objective: We explore new ways to control the properties of ferromagnetic films and nanostructures by the application of an electric field across an adjacent ferroelectric layer. Driving of magnetic domain walls by an electric field without the assistance of a magnetic field or spin-polarized current is one of the focus points.
Project Duration and Timing: 5 years (2012 – 2017)
Project Funding: European Research Council
MAIN CONTACT
Prof. Sebastiaan van Dijken Prof. Sebastiaan van Dijken heads the Nanomagnetism and Spintronics Group at Aalto University. Previously, he worked at the IBM Almaden Research Center (USA), Trinity College Dublin, and VTT (Finland). Sebastiaan van Dijken holds a PhD in Applied Physics from the University of Twente (Netherlands). Current research interests include electric- field control of ferromagnetism, ferroelectric tunnel junctions, and magnetoplasmonics.
Contact: Tel: +358-503160969 Email:
sebastiaan.van.dijken@
aalto.fi Web:
http://physics.aalto.fi/groups/ nanospin/
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