possible to recognize those metallic particles which are suitable for use in high density recording media and to engage in experimentation to determine what methods of manufacturing are required for the production of suitable high density recording particles surprisingly following the recognition of the problem it has been found that production of cobalt phosphorus particles by controlled chemical reduction in a d c magnetic field of at least about 200 gauss consistently produces magnetic particles having w h c of about 1 2 or less in the absence of a d c magnetic field of at least about 200 gauss cobalt phosphorus particles having a w h c as low as 1 2 are rarely produced application_number US 44986174 A description in the preparation of the cobalt phosphorus particles of the present invention the d c magnetic field is present during the reaction to form the metal particles after particle formation the cobalt phosphorus is separated from the reaction mixture washed with water and or organic solvents and then dried preferably under non oxidizing conditions to enhance their dispersion characteristics the dried particles may be reacted with a solution containing sulfuric acid in accordance with the teaching of copending u s application serial no 393 258 now u s pat no 3 905 841 assigned to the assignee of the present application in other instances dispersion characteristics may be improved by making ultrafine particles with large surface area as described in the following example v regardless of which technique is utilized the powder samples prepared in accordance with the present invention are measured for example with a 60 cycle vibrating sample magnetometer vsm to determine their minor and major loop characteristics and other magnetic properties when desired determination of the.