Effect of B content on the magnetic properties, phase evolution, and aftereffect of nanocrystalline FeCoPtB ribbons

Effect of B content on the magnetic properties, phase evolution, magnetic after effect, and the activation energy (E-a) for the melt- spun [(Fe0.7Co0.3)(0.725)Pt-0.275](100-x)B-x (x=14-18) ribbons has been investigated. Sufficient amount of boron addition effectively decreases the activation energy of ordering transformation, and also refines the grain size of the studied ribbons after thermal annealing, resulting in the improvement of H-i(c) from 3.4 kOe for x=14 to 6.2 kOe for x=18. The highest permanent magnetic properties of B-r=10.1 kG, H-i(c)=5.4 kOe, and (BH)(max)=15.7 MGOe can be achieved in [(Fe0.7Co0.3)(0.725)Pt-0.275](85)B-15 ribbons. Meanwhile, the magnetic after effect study evidences that the activation volume is reduced with the increase in B content from V=41.33x10(-19) cm(3) for x=14 to V=21.71x10(-19) cm(3) for x=18, arisen from the lower volume fraction of magnetically soft phases and the stronger exchange-coupling effect between magnetic grains. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068466]