Eddy‐Current Confined Cu/Al 2 O 3 /Nb/Fe 20 Ni 80
Xiaofeng Pu, Zhijun Sheng, Fu Liu, Huaidong Li, Zhoulu Yu, Zhaochen Liu, Baorui Xia, Jiaxing Chai, Changjun Jiang, Guozhi Chai, Daqiang GaoABSTRACT
Magnetic‐label biosensing requires sensing platforms capable of resolving weak stray field signals from low‐abundance biomarkers. In orthogonal fluxgate (OFG), the achievable detection limit is largely determined by the equivalent magnetic noise, which is closely linked to dynamic magnetic loss in the soft magnetic core. However, conventional Cu/FeNi composite wire cores contain continuous conductive interfaces. These interfaces readily induce radial current leakage and large‐scale eddy‐current loops, thereby increasing noise. To address this issue, we construct an interface engineered Cu/Al 2 O 3 /Nb/Fe 20 Ni 80 multilayer wire core for eddy‐current confined low noise OFG sensing. The Al 2 O 3 layer blocks radial current leakage between the Cu core and Fe 20 Ni 80 shell. The nanocrystalline‐amorphous Nb seed layer enhances interfacial scattering and refines Fe 20 Ni 80 grains, shortening current pathways. As a result, the multilayer core shows a 4.7‐fold resistance increase at 200 kHz, a 70.36% reduction in circumferential dynamic hysteresis loop area, and a 28.5% decrease in effective damping coefficient. Consequently, the equivalent magnetic noise of the OFG at 1 Hz decreases from 59 to 25 pT/√Hz. As an application demonstration, the platform detects magnetic beads down to 100 pg/mL and enables prostate‐specific antigen detection with a detection limit of 100 fg/mL and a linear range from 100 fg/mL to 100 ng/mL.