Method of making a permanent magnet sensor element with a soft m

Details Method of making a permanent magnet sensor element with a soft m Method of making a permanent magnet sensor element with a soft m

1989-08-28

1991-12-24

Sheehan, John P.

Metal treatment

Process of modifying or maintaining internal physical...

Magnetic materials

296021, 32420722, 21912116, 21912117, 21912165, 21912166, H01F 102

Patent

active

050749293

ABSTRACT:
A speed sensor is made by assembling a permanent magnet, a soft magnetic layer on the magnet, a magnetoresistive sensor element of the soft magnetic layer, and a toothed ferritic member mounted for movement past the sensor element. The permanent magnet is surface treated to form, in situ, the soft magnetic layer comprising a thin layer of high permeability, low coercivity material. An Nd-Fe-B alloy magnet is surface treated by a laser or electron beam to melt a thin layer which is cooled to resolidify into a soft magnetic material. Rapid cooling achieves an amorphous surface layer having the desired properties. Slow cooling results in the formation of alpha-iron grains which enhance the soft magnetic properties. Iron formation is aided by reacting with an oxidizing atmosphere. Iron alloying by adding iron powder to the molten layer is also discussed.

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