An Investigation on the Magnetic properties of some permanent magnet materials

Abstract

A brief review of modern permanent magnet materials and of their application in industry is followed by an account of an investigation on the magnetic properties of several alloys of the well-known Alni and Alnico types. The alloys which were prepared in a high frequency induction furnace and cast in sand moulds contained approximately 13%-25% nickel, 10%-15% aluminium with or without 3%-5 % copper and 5%-22% cobalt with iron as balance in each case. The magnetic properties of the alloys were determined by drawing ballistically the complete hysteresis curve. Adequately high values of induction were secured by magnetising the specimen in a specially constructed water cooled solenoid which can produce uniform magnetic fields of the order 2500-3000 oersteds over lengths of about 15 cm. The results of these experiments are generally in conformity with those of other leading workers. Several of the alloys studied had excellent magnetic properties- coercive force in excess of about 500 oersteds and remanence well above 6000 gauss. The alloys were studied in a variety of heat treated conditions to determine the optimum conditions of heat treatment in each case to secure the best magnetic properties. It was found that alloys containing Magnetic properties of some permanent magnet materials require comparatively faster cooling than those containing also copper and cobalt. Copper can also replace nickel to some extent without impairing the magnetic properties. Cobalt has a similar effect but has a more pronounced effect on the heat treatment schedule. The paper also gives the magnetic properties of a few of these alloys heat treated under strong magnetic fields.