A Way Forward? (Not necessarily “The Way Forward”) - PowerPoint PPT Presentation

J N Chapman, University of Glasgow

Synopsis

• Indicators of activity
• Magnetism in the late 20th century
• A firm base within the UK?
• Some possible ways ahead

MORIS NdFeB 99

Hard ferrite magnets ISEM

Intermag TMRC

Soft magnetic materials TISD

Int Conf on Electrical Machines and Drives

Major sessions at:

MRS APS

COMPUMAG ISEF

In the 3 months leading up to this conference, Magnews listed 37 conferences!

January - June 1999

• Europe plans magnet facility (1/99)
• Thin films squeeze out domains (1/99)
• Colossal magnetoresistance (2/99)
• Spinning electrons could lead electronics revolution (3/99)
• Magnets, molecules and quantum mechanics (3/99)
• Magnetoelectronics (4/99)
• Weak ferromagnet challenges theorists (4/99)
• Faster magnetic memory (6/99)

January – June 1992

• Are environmental magnetic fields dangerous (1/92)
• Fundamental effects in a spin (5/92)

Magnetic phenomena are studied:

• on length scales from nuclear to planetary
• on time scales from fs to geological
• over temperature ranges from K to GK
• over field ranges from fT to >100T

Magnetics runs through Physics, Chemistry, Materials Science, Metallurgy, Engineering, IT.

• There are close materials links to metals and oxides, especially superconductors, optical materials and semiconductors.
• Generic technologies of importance include thin films, growth & processing, material characterisation.

An exciting area of condensed matter science involving exotic metals and complex oxides

• Close links to superconductivity
• Extension to lower temperature and higher fields reveals wealth of novel behaviour (non-Fermi liquid behaviour, quantum fluctuations, magnetic quantum oscillations)

Magnetism in superlattices and magnetic chains

Interfacial phenomena

• Interface and surface anisotropy
• Spin dependent transport (metal-metal, metal-semiconductor, metal- insulator, etc.)
• Tunneling, Coulomb blockade, spin transistor

Based on Mn oxides with the perovskite structure.

• Perovskite structure is ‘natural laboratory for studying strongly correlated electron systems’ (coupling between electrons and lattice, competition between kinetic energy of mobile electrons and repulsive Coulomb interaction, etc.); control is achieved by doping.
• Manganites are almost fully polarised.
• Key features include the role of phonons at the metal/insulator transition, nature of the ground state, effect of interfaces on polarisation, phase separation, surface magnetisation, local disorder due to doping.
• MR >> 100% in fields of a few Tesla.

Potential for devices? - need for good room temperature performance at low fields.

• Defect-free interfaces, introduction of controlled defects, exploration of tunneling transport in complex oxides having intrinsic multilayer structures.

• GMR arises due to spin-dependent scattering.
• It occurs in magnetic multilayers, granular magnetic solids, spin-valves (SVs), spin tunnel junctions (STJs). SVs and STJs offer MR values of 10-40% and sensitivities of few %/Oe.
• The basic mechanism is reasonably understood but detail is lacking and the GMR effect is not yet fully exploited (for example, effect of a domain wall at a point contact).

Application areas are sensors (recording heads, positional for automotive application, navigational, etc.) and storage (MRAMs).

Scientific and technological challenges include:

• layer thickness control with decreasing stack thickness
• exchange biasing of the pinned layer
• performance retention after patterning

A branch of nanoscience and technology which offers:

• new phenomena as the dimensions of a magnetic structure fall below various characteristic magnetic length scales (e.g. spin diffusion length, domain wall width)
• a way of tailoring magnetic properties through variation of the size and shape of magnetic elements - “spin engineering”

Scope for innovation in:

• selecting the systems to be patterned and the form of the resulting patterned elements
• devising ways in which patterning is carried out (advanced lithographies, reactive ion etching, mask irradiation, probe microscopies, mass replication methods)

Technological driving forces include ultra-small sensors, MRAMs, quantum discs, spintronics.

Magnetic recording - hard disc and tape

• Phenomenal growth over the last decade due to near-insatiable demands to store data.
• Key issues now are what limits the density at which we can store information, the time required to write and access it and the period of time over which the medium retains it.
• Challenges span materials with improved magnetic properties, through developing sophisticated micromechanical drives, to optimisation of the recording channel and coding.

As recording densities increase beyond ~70GB/sq.in, and for special applications, other technologies may be/are required:

• recording on perpendicular media or discrete media (quantum discs), magneto- optic recording, hybrid magnetic - MO recording, magnetic random access memory (MRAM)

Spintronics encompasses GMR, spin-dependent tunneling and spin-injection devices.

MRAM

• non-volatile, radiation hard, speed of SRAM (<3ns), density of DRAM, low power (0.005x), low cost (0.1x), infinitely cyclable

Coherent spin transport in semiconductors looks encouraging following 2 recent discoveries

• at room temperature, optically induced spin-states have been found to be very long lived
• ferromagnetism exists in semiconducting GaMnAs

Once the physics and materials aspects are solved, spin enhanced and enabled electronics, spin filters, spin FETs, quantum spin-electronics, coherent spin electronics are anticipated.

Control through growth conditions, processing and patterning

• Final performance depends on interplay between intrinsic and extrinsic properties
• Strong role for theory and modelling in a multi-parameter space

Increased need to measure both structural and magnetic properties as completely as possible

Importance of interfaces

• Understanding and exploitation of MR phenomena (depolarisation of carriers in GMR and especially CMR materials)
• Control of surface anisotropies (property control in ultra-thin films)
• Coupling between grains in hard magnetic materials and ultra-high density recording media

In-house characterisation

• Ultra-fast measurements (pump-probe - sub-ps)
• High spatial resolution imaging (MFM with novel sensor heads, in-situ TEM)
• Sophisticated magnetometry (micro-magnetometers, minor loops, time dependence over ‘decades’)
• In-situ and ex-situ analytical techniques (spin-polarised techniques, STM, AFM, Auger, EELS)

Characterisation using Facilities

• Neutrons, X-rays, Ultra-high fields

X-ray magnetic scattering

• Resonant enhancement of magnetic scattering, element specific magnetic studies
• Dichroism studies (circular and linearly polarised), x-ray microscopy
• Separation of spin and orbit contributions to the magnetic behaviour of materials

100T magnet - pulsed fields ~10ms duration

• Investigation of new physics along the field axis of the phase diagram
• Understanding in strongly correlated electronic systems of the underlying many-body physics, including magnetic quantum critical phenomena
• Application to high anisotropy intermetallics, metallic superlattices, doped oxides, spin-liquids

Rare earth - transition metal magnets (Fe and Co-based) are the subject of most research.

• Annual growth rate of sintered NdFeB magnets ~12%, of bonded NdFeB magnets ~20%
• Partly fuelled by global growth of PCs but other areas promising including MRI, industrial robotics, mobile phones
• Largest potential is in electric vehicles

Challenges include:

• Materials suitable for operation at high temperature (~180C)
• Improved corrosion resistance
• Cost-effective production methods, recalling that the microstructure dominates the properties of permanent magnet materials

Automotive:

Starter motors, anti-lock braking systems (ABS), motor drives for wipers, injection pumps, fans and controls for windows, seats etc, loudspeakers, eddy current breaks, alternators

Telecommunications:

Loudspeakers, microphones, telephone ringers, electro-acoustic pick-ups, switches and relays

Data Processing:

Discs drives and actuators, stepping motors, printers

Consumer Electronics:

DC motors for showers, washing machines, drills, citrus presses, knife sharpeners, food mixers, can openers, hair trimmers etc., low voltage DC drives for cordless appliances such as drills, hedgecutters, chainsaws, magnetic locks for cupboards and doors, loudspeakers for TV and audio, TV beam correction and focusing device, compact-disc drives, home computers, video recorders, electric clocks, analogue watches

Electronic and Instrumentation:

Sensors, contactless switches, NMR spectrometer, energy meter disc, electro-mechanical transducers, crossed field tubes, flux-transfer trip device,

Industrial:

DC motors for magnetic tools, robotics, magnetic separators for extracting metals and ores, magnetic bearings, servo-motor drives, lifting apparatus, brakes and clutches, meters and measuring equipment

Astro and Aerospace:

Frictionless bearings, stepping motors, couplings, instrumentation, travelling wave tubes, auto-compass

Biosurgical:

Dentures, orthopaedics, wound closures, stomach seals, repulsion collars, ferromagnetic probes, cancer cell separators, NMR body scanner

• Progress continues in FeSi and in soft amorphous and nanocrystalline alloys
• The scale of use of FeSi makes reductions of loss of a fraction of 1% significant
• (Fe, Co, Ni)(Si, B) plus additions are developed for specialist applications and there is scope for innovation here
• Modelling on various length scales (micromagnetic, hysteresis and finite element) and finding ways of linking them will lead to more efficient machines and motors
• Understanding how materials respond under varying combinations of field and stress is scientifically challenging and is the key to new and improved applications
• Amorphous wires with near zero magnetostriction and with a strong negative magnetostriction offer exciting possibilities for many sensor applications through the giant magneto-impedance and the stress impedance effect

Improved performance, increased energy efficiency and the enabling of applications not previously possible is being realised with the help of:

• advanced magnetic materials
• powerful design and analysis programmes

Examples of innovation include:

• embedded machines in aero engines operating at high temperatures, with magnetic bearings replacing mechanical bearings
• soft, high-resistivity composites for magnetic bearings running at up to 60,000rpm in vacuum; with appropriate magnetic circuit design hysteresis is almost eliminated and losses are minimised
• multi-degree of freedom actuators incorporating high energy product magnets and operating at 200Hz for force feedback joysticks usable in surgery and other active vision systems, including computer games

• High Temperature (800oC) Linear Actuator
• 24% Cobalt Iron
• Ceramic Insulated, Nickel plated copper windings
• 300N, 0.5mm stroke
• Linear permanent magnet actuator
• for textile machinery
• 200mm stroke
• Peak acceleration of 100g

• Aerospace Electrohydraulic surface actuator
• Technology Demonstrator for Airbus A3XX
• 55kW, Brushless NdFeB Permanent Magnet Motor
• Brushless Permanent Magnet Machine
• 120,000rpm (100mm OD)
• Carbon Fibre / NdFeB / Epoxy composite rotor

There are scientific, technical and engineering opportunities in profusion - how can the UK take best advantage?

UK background

• The total number of workers in academia and industry in magnetism is considerable (for example, there are 500 academic researchers).
• With a few notable exceptions, activity is concentrated in small units in industry and academia.
• There is a danger of sub-criticality.
• Collaboration and networking are seen as the best way of avoiding the danger of sub-criticality.

• Learned societies and industrial clubs/trade associations - IoP, IoM, IEE, IEEE, UK MagSoc, TRIUMF…. (for example Joint Magnetics Workshop)
• DTI (LINK scheme in Storage and Displays, UKISC)
• Foresight
• Seagate Technology Plan
• Europe Framework 5 (opportunities for links to elsewhere in Europe)
• EPSRC

Objectives

• Encourage new links between companies and science & engineering base
• Involve > 20 organisations (including > 10 SMEs) in collaborative projects
• Stimulate exploitation of academic research
• Encourage supplier-user and small - large company relationships
• Develop UK information storage community

Proposed budget

• ~£8M plus matching funds from industry

Proposed launch

• End 1999/beginning 2000

Magnetism and Magnetic Materials Initiative (1989 - 1994)

• Advanced Magnetics Programme (Physics and Materials) - due to end 2000
• Machines and Drives (Engineering) - ended 1998
• Responsive mode (notable take-up in fundamental condensed matter physics) - continuing

What next?

• The next 6 months provide an opportunity for you to advise programmes managers of what you would like to happen and why!

Another managed programme?

• Bad fit to current EPSRC policy but would protect those aspects of the programme at the physics/materials & materials/engineering interfaces which arguably contain some of the most exciting possibilities for the future.

Return to responsive modes in Physics, Materials and Engineering?

• Encourage EPSRC to ensure that assessment panels are chosen which contain representatives from more than one programme area.

If there is no EPSRC coordinator, will the UK (academic) magnetics community fragment?

Suggestion:

• Establish EPSRC Networks involving both academics and industrialists.
• Use these as fora to decide (non-exclusive) priorities for different aspects of magnetics.
• Set aside some of final round of AMP money to fund these.

Purpose:

• Help carry forward existing collaborations and provide springboard for new ones so that small individual groups can make maximum impact.
• Provide a harmonious way to keep UK magnetics competitive and at the leading edge.

• At the end of the 1980’s UK magnetics was weak; at the end of the 1990’s this is no longer the case.
• The momentum and cohesion built up over the last decade must not be allowed to evaporate.
• A diffuse non-interacting academic community will never maintain a high profile with government, industry, EPSRC and is unlikely to make an impact internationally.
• Significant organisational change (for academics at least) is inevitable in the next 12 months but there is a short time window open to try to influence the nature of the change; this opportunity must be taken!