ENGRI111_23_magneticsIII - Small regions tend to...

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ENGRI 111 ENGRI 111 Magnetics - III Magnetics - III Superparamagnetism Ferrofluids
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hyperphysics.phy-astr.gsu.edu/Hbase/solids H H H Hard Soft
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Requirements Requirements Head Easily magnetized and demagnetized High permeability (slope of M vs. H) Loose very little energy as heat Tape High remanent magnetization - produces sufficient field above the disc High coercive field – information is not erased too high coercivity requires high fields
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Curie Temperature Curie Temperature Material Curie T (K) Fe 1043 Co 1388 Ni 627 Fe 3 O 4 858 CrO 2 386 www.geol.binghamton.edu
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Magnetic Read/Write: Requirements Magnetic Read/Write: Requirements
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What is the Limit? What is the Limit? Can we increase storage density by continuously shrinking the area of disc, where information has been written? High storage density requires high coercive fields
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Unformatted text preview: Small regions tend to demagnetize easily Single Domain Particles Single Domain Particles http://lmis1.epfl.ch Superparamagnetism Superparamagnetism In very small particles the energy required to change the direction of magnetization is comparable to thermal energy Single domain particles Particles exhibit behavior like paramagnetic materials Superparamagnetic Particles Superparamagnetic Particles Hysteresis Loop Hysteresis Loop Superparamagnetic Paramagnetic Ferromagnetic Solutions Solutions Use an antiferromagnetic layer to stabilize superparamagnetic particles Perpendicular recording www.nature.com k: Boltzmanns constant, T: temperature Parallel/Perpendicular Storage Parallel/Perpendicular Storage www.physorg.com 100-200 Gbit/in 2 1000 Gbit/in 2...
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ENGRI111_23_magneticsIII - Small regions tend to...

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