Influence of Al addition on structural, crystallization and soft magnetic properties of DC Joule annealed FeCo based nanocrystalline alloys

•Minor Al addition in FeCoBSiNbCu alloy system promotes amorphous structure stabilization.•The Al added alloy shows distinct and favourable nanocrystallization behaviour.•DC Joule annealing technique under longitudinal magnetic field promotes good magnetic softness.•The Al added alloy shows improved magnetic field induced anisotropy (Ku) during longitudinal field assisted Joule annealing.•The magnetic properties and microstructural properties are in agreement with the extended-random anisotropy model. The effect of minor Al addition on structural, crystallization, soft magnetic behaviour and magnetic field induced anisotropy through DC Joule annealing in (Fe53.95Co29.05)83Si1.3B11.7-xNb3Cu1Alx, (X=0, 1) alloys has been studied. The Al added as-quenched melt spun ribbons show good glass forming ability, better thermo-physical properties like a high Tx1 of 438°C, Tcam of 435°C and Tcnc of 906°C, compared to Tx1 of 389°C, Tcam of 409°C and Tcnc of 900°C for the alloy without Al addition. The longitudinal magnetic field annealed Al added alloy exhibits low Hc of 12.92A/m and maximum Ms. of 1.78T. The better soft magnetic properties of Al added alloy are achieved through a high nucleation density of BCC-FeCo(Al) nanocrystallites having low K1 and λ values. The as-quenched alloys possess high magneto-strain exceeding 30ppm and approach near zero value on nanocrystallization. The longitudinal magnetic field assisted DC Joule annealing, having current density (J) in the range of J=20–25A/mm2 promotes good magnetic softening due to precipitation of 5–35nm nanocrystallites as explained by extended-random anisotropy model. The Al added alloy shows better magnetic field induced anisotropy (Ku) on nanocrystallization and shows visible change in the shape of hysteresis loop.