A high coercivity bias piece for making acousto-magnetic labels is made of an alloy strip with 10-14% weight percent Mn, less than 7% weight percent of one or more other transitional metals, with the balance Fe, after cold rolling to final gage, going through a final aging heat treatment at below 590 C, longer than 5 minutes. The strip thickness is 0.065-0.18 mm with coercivity measured by direct current method being 56-90 Oe. The method of making the high coercivity bias piece is to cold roll the strip to 0.07-0.15 mm with aging temperature at 450-570 C, for 0.5-20 hours to form a magnetic strip with coercivity of 60-85 Oe, followed by cutting the strip to required size. This high coercivity bias piece is manufactured without expensive Co and Ni materials, showing that a low cost Fe-(10-14% weight percent Mn) based alloy can be used to make high coercivity bias.