Enhanced soft magnetic properties and magnetocaloric effect in B substituted amorphous Fe–Zr alloy ribbons

Magnetic properties and magnetocaloric effect in amorphous Fe89−xBxZr11 (x = 0–10) alloys prepared by melt spinning technique have been investigated. The crystallization temperature, Curie temperature (TC), and room temperature saturation magnetization (MS) of the alloys increase almost linearly with B addition. Coercivity decreases from 13 Oe to 0.015 Oe with the addition of 5 at.% B and then increases to 0.063 Oe for the alloy with 10 at.% B. Low temperature thermomagnetization curves of Fe89Zr11 alloy show a bifurcation between field-cooled and zero-field-cooled curves below 35 K. No such bifurcation was observed in the alloys containing B. High temperature thermomagnetic curves indicate an amorphous-to-crystalline transition above 800 K corresponding to the precipitation of α-Fe phase. These studies reveal that addition of B not only enhances the crystallization temperature, but also decreases the degree of competition between ferromagnetic and antiferromagnetic interactions and there by enhances the soft magnetic nature of the alloys. Magnetic domain structure shows large-sized domains with smooth and relatively straight domain walls for the Fe84B5Zr11 alloy. The magnetic domain structure analysis is used to understand the origin of the ultralow coercivity in these alloys. Due to the enhanced soft magnetic properties of these alloys and the possibility of tuning TC and MS by B addition, change in magnetic entropy (ΔSM) was also investigated. ΔSM showed enhancement from 1.3 J/(kg-K) for the Fe89Zr11 alloy to 1.73 J/(kg-K) for the Fe79B10Zr11 alloy for a field change of 0–18 kOe.