Influence of b content on the magnetostrictive properties of single-crystalline, poly-crystalline, and amorphous fe-co-b alloy films

(Fe0.7Co0.3)100–xBx (x = 0–15, at. %) alloy films of 100 nm thickness are prepared on VN(001) single-crystalline underlayers at 600 °C and on VN poly-crystalline underlayers at room temperature (RT). A high substrate temperature of 600 °C is used to promote epitaxial film growth on VN(001) underlayer. Influences of B content on the structural, magnetic, and magnetostrictive properties are investigated. The films formed on VN(001) underlayers involve bcc(001) epitaxial crystalline phase, whereas those formed on VN poly-crystalline underlayers consist of poly-crystalline and/or amorphous phases. Surface roughness of film formed on VN(001) underlayer at 600 °C increases with increasing the B content, whereas flat surfaces are realized for the films formed on VN poly-crystalline underlayers at RT. The surface morphology is influenced by both the substrate temperature and the B content. The films with flat surfaces show good soft magnetic properties. In contrast, rough surface causes an increase in the saturation magnetic field. In the case of films formed on VN(001) single-crystalline underlayer at 600 °C, magnetostriction value of λ100 increases from +200 × 10–6 to +310 × 10–6, as the B content increases from x = 0 to 5. With further increasing the B content, λ100 value decreases due to unsaturation of magnetization at a magnetic field of 1200 Oe which is the maximum value used for measurement. λ111 values are nearly zero (–10 × 10– 6 – +20 × 10–6 ) for all the investigated B contents. Slight addition of B atoms around 5 at. % is effective in enhancing the λ100 value, while keeping high crystallographic quality, flat surface, and soft magnetic property. On the contrary, the films formed on VN poly-crystalline underlayers at RT show moderately large λ values of about +60 × 10–6 for all the B contents. The present study shows that control of B content and realization of flat surface are important factors in enhancing the magnetostriction of Fe-Co-B film. © 2021, Magnetics Society of Japan. All rights reserved.