Structure And Magnetic Properties Of Nanocrystalline Fe-Co-Nb(V)Si-B-Cu Soft Magnetic Alloys

The magnetic properties and structure of FeCo-based (Fe_0.5Co_0.5)_73.5Nb₃Si_13.5B₉Cu₁ and(Fe_0.5Co_0.5)_73.5Nb₂V₁Si_13.5B₉Cu₁ alloys annealed at different temperature were investigated. Itis shown that the good magnetic properties can be obtained when the two alloys is annealed at460℃, which is lower than that of FINEMET alloys. With increasing annealing temperature, thecrystallite size becomes larger, which makes the initial permeability decrease.When heated up tothe end of the second DSC exotherm, some boride-type phases mainly Fe2B,(FeCo)₂₃B₆ areformed, which makes magnetic properties harden quickly.The Curie temperature of as-quenched (Fe_0.5Co_0.5)_73.5Nb₃Si_13.5B₉Cu₁ and(Fe_0.5Co_0.5)_73.5Nb₂V₁Si_13.5B₉Cu₁ alloys is almost the same about 460℃which is much higherthan that of Co-free Fe_73.5Nb₃Si_13.5B₉Cu₁ and Fe_73.5Nb₂V₁Si_13.5B₉Cu₁ alloys. After the optimumisothermally annealing at 460℃for 30s in vacuum, the initial permeabilityμi of(Fe_0.5Co_0.5)_73.5Nb₃Si_13.5B₉Cu₁ alloy can keep a constant up to 300℃, while the initialpermeabilityμi of (Fe_0.5Co_0.5)_73.5Nb₂V₁Si_13.5B₉Cu₁ alloy,which is obtained from partiallyreplacing Nb by V, could only keep a constant up to 200℃. Moreover, as the temperature iselevated to 320℃, the initial permeability of (Fe_0.5Co_0.5)_73.5Nb₂V₁Si_13.5B₉Cu₁ alloys wouldbecome less than that of (Fe_0.5Co_0.5)_73.5Nb₃Si_13.5B₉Cu₁ alloys. On the other hand, increasingannealing temperature can make the initial permeability more stable at high temperature, forexample, the initial permeability of 580℃annealed sample can keep less decrease below 600℃which is significant for seeking new high-temperature soft materials.The dependence of the products of initial permeabilityμi and relaxation frequency ofdomain wall motion fo on different annealing temperatures was also studied by using animpedance analyzer. It is shown that the initial permeabilityμi and relaxation frequency ofdomain wall motion fo closely depended on the restoring coefficientα. Overannealing resultsin a drastic decrease of the initial permeability and a significant increase in relaxation frequencyfo .