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Details of Grant 

EPSRC Reference: EP/C52022X/1
Title: Picosecond Magnetization Dynamics of Mesoscopic Magnetic Tunnel Valves
Principal Investigator: Hicken, Professor R
Other Investigators:
Researcher Co-Investigators:
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Department: Physics
Organisation: University of Exeter
Scheme: Standard Research (Pre-FEC)
Starts: 01 May 2005 Ends: 30 April 2008 Value (£): 273,263
EPSRC Research Topic Classifications:
Materials Characterisation Materials Processing
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Summary on Grant Application Form
A magnetic hard disk drive can be found in almost every personal computer. As the amount and complexity of the information that we manipulate continues to grow, it is necessary for the storage capacity and speed of the disk drive to increase. Data is stored in concentric circular tracks on the surface of the disk. A short section of track is magnetized either parallel or anti-parallel to its circumference so as to represent a single digit of binary code, a 1 or 0 . or bit . Increased storage capacity is achieved by reducing the physical size of both the bits, and the transducers that read and write the data. This proposal is concerned with the high-speed magnetic response of the materials that will be used to read the data in the next generation of disk drives.At present the data is read with a spin-valve device. This is based upon two ultrathin layers of magnetic material separated by an ultrathin layer of copper. When a magnetic field is applied to the device, the magnetic moment of one of the layers (the free layer) changes its direction. in the same way that a compass needle responds to the earth's magnetic field, while the other pinned layer remains fixed. The electrical resistance measured in the plane of the layers may change by up to 15% as a result. When this device passes over the surface of the disk, the orientation of the magnetic moment of the free layer changes in response to the magnetic field emanating from the bits, and data is read back by measuring the change in resistance of the spin-valve. As the spin-valve is made smaller it becomes necessary to increase the percentage change in resistance so that data can be read back against a background of electrical noise. The data storage industry is therefore planning to move to tunnel-valve structures that yield changes of resistance of greater than 40%. The layer of copper is replaced with an ultrathin insulating layer, so that current can instead be passed vertically between the magnetic layers by the quantum mechanical process of tunneling . At the same time. the lateral dimensions of the multilayer must be reduced to about 50 nm (50 billionths of a meter) to match the smaller bit sizes that are required.It is essential to understand how easily and how quickly the free layer magnetic moment can change its direction. and whether it can be thought of as a single compass needle or if instead different regions of the tunnel valve respond differently to the magnetic field. The effect of applying a pulse of magnetic field is similar to that of dropping a pebble into a tank of water. Waves of magnetization (spin waves) are generated and reflected backwards and forwards from the edges of the tunnel valve device in which they are confined. By carefully studying the spin waves that are excited. we can deduce how easily and quickly the magnetization should change direction. This is an excellent example of how basic scientific understanding can help solve a major technological problem.We propose to observe both the generation of spin waves and the change in direction of the free layer magnetic moment in high quality tunnel-valves with lateral dimensions in the range of 50 nanometres to 10 microns. which will be supplied by Hitachi. The tunnel valve will be excited repetitively with either short magnetic field pulses or by a sine wave magnetic field with a period of less than 1 nanosecond. Pulses of light of about 100 femtoseconds 11 Oe-13 s) duration will be used as a strobe light to freeze the response of the tunnel valve at any time during its response to the magnetic field. By connecting together frames acquired at different times we will be able to build up movies that show either the propagation of spin waves or the magnetic moment as a whole changing its direction.Section 1-3 Date Footed: 29.'7.'04 16:
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