Superior high-temperature magnetic softness for Al-doped FeCo-based nanocrystalline alloys

The temperature dependence of initial permeability (μi-T), the average grain size (D), the Curie temperature of amorphous phase (Tcam) of a series of annealed (Fe0.5Co0.5)73.5Nb3Si13.5Cu1B9 − xAlx (x = 0, 1, 2, 3) alloys were investigated. The Curie temperature of amorphous phase (Tcam) for the Al-contained alloys decreased compared with the Al-free alloy, but the high-temperature magnetic softness was improved. It was found that the increasing Al content enlarged the interval temperature (ΔTx) between the onset crystallization temperature (Tx1) and the secondary crystallization temperature (Tx2). The μi of 530 °C vacuum annealed samples tended to increase both at room temperature (except for x = 3 alloy) and elevated temperature when Al replaced B element. The (Fe0.5Co0.5)73.5Nb3Si13.5Cu1B6Al3 alloy exhibited excellent high-temperature magnetic softness, and its higher μi above 1000 can be maintained up to 670 °C.