A method of forming a micromagnetic device including providing a substrate and forming a magnetic core layer over the substrate from a magnetic alloy. The magnetic alloy includes iron, cobalt and phosphorous. A content of the cobalt is in a range of 1.8 to 4.5 atomic percent. A content of the phosphorus is in a range of 20.1 to 30 atomic percent. A content of the iron is substantially a remaining proportion of the magnetic alloy.