Nonmagnetized permanent magnet material is heated in a pattern by a laser beam to a localized temperature above the Curie point or a temperature sufficient to reduce the coercivity sufficiently for an external field to magnetize the pattern in the direction of the field. Magnets so produced can have very high pole density, digital encoding and analog patterns having gradually varying local field strength. Alternating pole magnets of this type can be used for stepper motor magnets.

Magnetically coded device

A magnetized or unmagnetized body of a permanent magnet material is heated in a pattern by a laser beam to a temperature sufficient to lower the coercivity of selected heated regions of the pattern and exposed to a magnetic field to magnetize or to remagnetize the selected heated regions. A pattern guide is used in the process to densify the pattern. In the process, energy is directed through the pattern guide and onto the selected regions, while the pattern guide prevents or minimizes heating of unselected portions of the body. Magnets so produced can have very high pole density, digital encoding and analog patterns having gradually varying local field strength.

A method for thermomagnetic encoding of permanent magnet materials

A permanent magnet is heated in a pattern by a laser beam to a localized temperature above the Curie point or a temperature sufficient to reduce the magnet coercivity sufficiently for the field of the magnet or an external field to remagnetize the pattern in the reverse direction. Magnets so produced can have very high pole density, digital encoding and analog patterns having gradually varying local field strength.

Thermomagnetically patterned magnets and method of making same

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.

Method of making a permanent magnet sensor element with a soft magnetic layer

A composite magnetic member formed of a single material having a ferromagnetic section with high soft magnetism and a non-magnetic or the like section with sufficiently low magnetic (feebly magnetized or non-magnetic) and sufficient low MS temperature and a process for producing the member are provided. A composite magnetic member made of a single material of martensitic stainless steel including Ni having two sections of a ferromagnetic section having maximum permeability not less than 200 and coercive force not more than 2000 A/m and a feebly magnetized section having permeability not more than 2 and MS temperature not more than -30° C. A process for producing a composite magnetic member, comprising the steps of locally heating a single material of martensitic stainless steel having particular composition including Ni and having ferrite and carbide, at temperature of more than austenite transformation temperature, and rapidly quenching it so that austenite structure is formed in the heated and quenched section which structure has MS temperature not more than -30° C.

Composite magnetic member and process for producing the member

The steels examined were a ferromagnetic carbon steel, S35C (equivalent to AISI 1035), and a nonmagnetic austenitic stainless steel, SUS 304 (equivalent to AISI 304). The gratings formed were magnetized in a 5.4-kOe field and the profile of the vertical component of magnetic flux leakage from each magnetized grating was measured. Changes of microstructure and mechanical strength of the beam-irradiated portions of the steel plates were also investigated. The measurements of the leakage flux profiles revealed the existence of remanent magnetism in the gratings. Metallographic and mechanical-hardness examinations showed that the original mixed ferrite/pearlite phase in the S35C steel was changed to martensite by beam irradiation. This increased its mechanical hardness. It was also determined that small grains of the ferrimagnetic ferrite phase were precipitated in the base of the nonmagnetic austenitic phase in the SUS 304. >

H. Ikeda

Papers

Formation of magnetic grating on steel plates by electron/laser beam irradiation