THIN FILMS OF ION-RHODIUM EXHIBITING A BROADLY HYSTERIC FIRST ORDER TRANSISTION BETWEEN THE FERROMAGNETIC AND ANTIFERROMAGNETIC STATES ARE PRODUCED BY SEQUENTIALLY DEPOSITING IRON AND RHODIUM FILMS UPON A REFRACTORY SUBSTRATE AT A PRESSURE IN THE RANGE OF 1X10**-6 TORR, ANNEALING THE STRUCTURE IN A VACUUM OF 1X10**-6 TORR AT A TEMPERATURE OF APPROXIMATELY 700* C. FOR 1 HOUR TO PRODUCE A COMPLETE DIFFUSION OF THE IRON AND RHODIUM LAYERS, AND SUBSEQUENTLY SUBJECTING THE DIFFUSED LAYERS TO A SECOND ANNEAL IN AN ATMOSPHERE GREATER THAN 10 PARTS PER MILLION OXYGEN IN A THERMAL CYCLE THAT INCLUDES SLOWLY HEATING THE STRUCTURE TO 400* C., MAINTAINING THE 400* C. FOR APPROXIMATELY 10 MINUTES AND SLOWLY COOLING TO ROOM TEMPERATURE. FILMS THUS FORMED ARE ADVANTAGEOUSLY EMPOLYED IN THE RECORDING OF DIGITAL INFORMATION BY ELECTRON BEAM HEATING INDIVIDUAL REGIONS THROUGH A FIRST ORDER TRANSISTION TO THE FERROMAGNETIC STATE WHEREUPON THE REGIONS ARE PERMITTED TO COOL TO A BIASING TEMPERATURE SLIGHTLY HIGHER THAN THE TEMPERATURE OF TRANSISTION BACK TO AN ANTIFEROMAGNETIC STATE. A MAGNETIC FIELD THEN IS APPLIED TO THE ENTIRE FILM TO MAGNETIZE ONLY THOSE REGIONS OF THE FILM IN THE FERROMAGNETIC STATE AND READOUT OF THE RECORDED INFORMATION CAN BE ACHIEVED BY CONVENTIONAL ELECTRON BEAM MICROSCOPY. THE FERROMAGNETISM OF THE FILM SUBSEQUENTLY CAN BE ERASED BY COOLING THE FILM BELOW THE TRANSISTION TEMPERATURE TO THE ANTIFERROMAGNETIC STATE OR BY THE APPLICATION OF A STRAIN TO THE FILM.