a glassy metal alloy consists essentially of the formula co a fe b ni c m d b e si f c g , where m is selected from molybdenum and &# 34 ; a &# 34 ;, &# 34 ; b &# 34 ;, &# 34 ; c &# 34 ;, &# 34 ; d &# 34 ;, &# 34 ; e &# 34 ;, &# 34 ; f &# 34 ; and &# 34 ; g &# 34 ; are in atom percent , &# 34 ; a &# 34 ; ranges from about 40 to about 43 , &# 34 ; b &# 34 ; ranges from about 35 to about 42 and &# 34 ; c &# 34 ; ranges from 0 to about 5 , &# 34 ; d &# 34 ; ranges from 0 to about 3 , &# 34 ; e &# 34 ; ranges from about 10 to about 25 , &# 34 ; f &# 34 ; ranges from 0 to about 15 and &# 34 ; g &# 34 ; ranges from 0 to about 2 . the alloy can be cast by rapid solidification into ribbon or otherwise formed into a marker that is especially suited for use in magneto - mechanically actuated article surveillance systems . advantageously , the marker is characterized by relatively linear magnetization response in the frequency regime wherein harmonic marker systems operate magnetically . voltage amplitudes detected for the marker are high , and interference between surveillance systems based on mechanical resonance and harmonic re - radiance is virtually eliminated .