Piezomagnetic Performance of Stress-Annealed FeAlB Alloys

Two FeAlB polycrystalline alloys were stress annealed and had the piezomagnetic behavior determined before and after the stress annealing (SA). The concentration of boron is constant, 1.6% (at%). The alloys are basically formed by the phase Fe
₂
B dispersed in a bcc matrix. The bcc matrix can be formed of a disordered and/or ordered structure, depending on ratio of Fe:Al, that was fixed as 86Fe:14Al and 80Fe:20Al. Magnetostriction and magnetic induction were measured as a function of magnetic field and compressive stresses. The piezomagnetic coefficient d
₃₃
≡ dλ/dH improvement due to SA was achieved, in which λ is the magnetostriction and H the applied magnetic field. SA causes the reorientation of the magnetic moment of the material creating an artificial magnetic anisotropy. The behavior of the coefficient d
₃₃
varies due to changes in Al content, since the magnetocrystalline anisotropy of the alloy depends on the ordering of the bcc matrix. Values of d
₃₃
up to 4 nm/A were reached for the polycrystalline alloy with 14% Al (at%) in an interval of compressive stresses of 0 ≤ |σ | ≤ 177 MPa. This large interval of compression stress is due to the presence of the Fe
₂
B phase.