ENGRI_1110_Lect17_09_posted

ENGRI_1110_Lect17_09_posted - Origin Of Magnetic Properties...

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Unformatted text preview: Origin Of Magnetic Properties Origin Of Magnetic Properties www.aacg.bham.ac.uk/.../magnetic_recording.htm Spin Moment Orbital Moment Ferromagnetic Fe, Ni Antiferromagnetic Cr, Mn Exchange Interaction: acts to align neighboring atoms Parallel: Ferromagnetic (not exactly what bulk magnets would do) Antiparallel: Antiferromagnetic Relationship of B and H Relationship of B and H Ferromagnetic materials when Ferromagnetic materials when formed into useful shapes do not formed into useful shapes do not start off permanently magnetized start off permanently magnetized Why??? 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 At C urie te m pe ra ture , the rm a l e ne rg y pre ve nts a lig nm e nt o f m a g ne tic m o m e nts in fe rro m a g ne ts Entro py e ffe c t Magnetic materials lower their energy by dividing into multiple domains Domains are costly – energy associated with their formation Domain Walls Domain Walls The thickness of magnetic walls is a balance between: Exchange energy which acts to keep its moment parallel to its neighbors (domain wall thick) Anisotropy energy which acts to keep all moments parallel to particular crystal direction (domain wall thin) Domain Walls Domain Walls www.aacg.bham.ac.uk/.../magnetic_recording.htm Magnetization Magnetization H = 0 H > 0 M H M H Domain Wall Magnetization Magnetization H >> 0 H >>> 0 M H M H Magnetic Hysteresis Magnetic Hysteresis Once a magnetic material is saturated, decreasing H again does not return M (or B) to the same position....
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This note was uploaded on 02/10/2010 for the course ENGRI 1110 at Cornell.

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ENGRI_1110_Lect17_09_posted - Origin Of Magnetic Properties...

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