Department of Physics, University of Hull

Dr. Alan Jenner (Senior Lecturer)
Mr. Neill Dearing (PhD student)
Mr. Richard Eastwood (PhD student)
Mr. Alan Heathcote (PhD student)

Research Interests

Magnetic Materials and Applications
The research activity of the Magnetics group covers fundamental magnetic properties of materials and their application in novel systems and devices. Of particular interest are materials that exhibit exceptional magnetoelastic behaviour, eg alloys and compounds containing Rare Earth elements which markedly affect their magnetostrictive properties. Work is also in place on studies of the properties and applications of novel magnetic shape memory alloys.

Materials preparation
Facilities are available for producing amorphous metal-metalloid (Fe-B) and metal-metal (Fe-Zr) alloys with additions of Rare Earths (Tb, Dy, Sm). Rapid quench techniques are used to achieve cooling rates of 106 K/s, allowing materials to be produced in ribbon, wire, or thin form.

X-ray diffraction and transmission electron microscopy show that atomic order is absent in 'as spun' material but other sensitive techniques are available to detect the onset of crystallisation. Subsequent magnetic annealing optimises the magnetomechanical coupling (yielding coupling coefficients 290%), rendering the material particularly useful for stress or strain sensors, non-contact torque sensors, and low frequency accelerometers.

Pulsed ablation deposition (PLD) has been used to grow high-quality films of magnetoelastic amorphous and crystalline Rare Earth transition metal alloys and compounds. These films can be patterned for use in basic physics studies and device applications.

Magnetism of amorphous nanocrystalline alloys and thin films
The presence of a random atomic structure in amorphous alloys has a strong influence on their magnetic behaviour. In alloys containing Rare Earths, random local anisotropy competes with exchange interactions and the magnetic structures can vary from ordered (eg ferromagnetic or sperimagnetic) to disordered states (spin glass or random anisotropy system) as the composition or temperature is varied. A vibrating sample magnetometer is available to allow magnetic transitions in these systems to be studied over wide applied field and temperature ranges.

Work is also in progress to develop these amorphous alloys for use as active and passive sensors which exploit the exceptional magnetoelastic coupling that is inherent in such materials. Studies of the correlation between the microstructure and magnetic structures in magnetic shape memory alloys are of interest as they are amenable to phase switching by magnetic means.

Crystalline Rare Earth compounds: NDT and applications
The ability of giant magnetostrictive materials such as Terfenol-D to produce high strains (~ 1500 ppm) with modest magnetic fields has been known for many years, but only recently have they become available in useful quantities. Current research is directed towards investigating their response to alternating or pulsed fields and their non-linear magnetomechanical behaviour.

Of particular interest is the application of magnetostrictive devices for active vibration control. Through collaborating with the Department of Engineering, we have been able to integrate these special magnetic materials with sophisticated control electronics, producing an anti-vibration system that offers far superior performance to the conventional passive spring and damper system. Working with a spin-out company we have seen the commercialisation of our magnetostrictive technology and the appearance of novel products such as the 'Soundbug' (Newlands Technology Ltd).

List of recent publications

High-power, low frequency magnetostrictive actuation for anti-vibration applications, P A Bartlett, S J Eaton, J Gore, W J Metheringham and A G Jenner, Sensor Actuat A-Phys 91, 133 (2001)
Magnetization and magnetostriction of melt-spun TbDyCeFe ribbons, C MacMahon, A G Jenner and H Ahlersn, IEEE T Magn 36, 3214 (2000)
Actuation and transduction by giant magnetostrictive alloys, A G Jenner, R J E Smith, A J Wilkinson and R D Greenough, Mechatronics 10, 457 (2000)
Amorphous magnetic materials for transducers, F Jerems, C MacMahon, A G Jenner and R D Greenough, Ferroelectrics 228, 333 (1999)
Pulsed laser deposition - an alternative route to the growth of magnetic thin films, A G Jenner, J P Hayes, L A Stone, H V Snelling and R D Greenough, Appl Surf Sci 139, 408 (1999)
Magnetic and magnetoelastic properties of thin films by pulsed laser deposition, J P Hayes, L A Stone, H V Snelling, A G Jenner and R D Greenough, IEEE T Magn 33, 3613 (1997)
Controlled high power actuation utilising Terfenol-D, M G Aston, R D Greenough, A G I Jenner, W J Metheringham and K Prajapati, J Alloy Compd 258, 97 (1997)
Magnetostrictive actuation performance under digital variable structure control, R J E Smith, A G I Jenner, A J Wilkinson and R D Greenough, J Alloy Compd 258, 101 (1997)
Magnetostrictive thin films by laser ablation deposition, A G Jenner, L A Stone and H V Snelling, J Alloy Compd 258, 138 (1997)
Nonlinear magnetization processes in twinned Terfenol-D crystals, A P Holden, J Kennedy, N Halliday, D G Lord and A G Jenner, J Appl Phys 81, 5712 (1997)