Temperature-tuned electrodeposited CoNiP as an internal bias layer for self-biased LiNbO 3 /Metglas DC magnetic-field sensor

Abstract Electrodeposited CoNiP is investigated as a material for a remanent magnetic biasing layer for self-biased magnetoelectric sensors. CoNiP coatings were deposited from a sulfate-hypophosphite electrolyte at temperatures between 40 and 55 °C while the remaining deposition parameters were held constant. Raising the electrolyte temperature resulted in an increase in the phosphorus concentration from 3.1 to 13.5 at.%, accompanied by a transition from an acicular crystalline morphology to a finer and more structurally disordered morphology. The in-plane coercive field decreased from 618 to 260 Oe, while the saturation magnetization decreased from 101.1 to 57.2 emu/g. The coating deposited at 40 °C, which exhibited the highest coercivity and magnetization, was used as a magnetization layer in an magnetoelectric (ME) composite structure based on a y+128°-cut bidomain LiNbO3 plate and 1K101 Metglas to form a self-biased laminate. Two flexural resonances were observed at 465 and 3393 Hz, with magnetoelectric coefficients of 193 and 117 V/(cm·Oe), respectively. A modulation frequency of 3396 Hz was selected because it combined a high magnetoelectric response with a low equivalent electric noise level. At zero external bias, the laminate exhibited a magnetoelectric coefficient of 103.3 V/(cm·Oe) at the modulation frequency and an approximately linear response from −1.10 to +1.04 Oe for a 10% nonlinearity criterion. The DC magnetic-field sensitivity was 17.6·103 V/T, corresponding to a limit of detection (LOD) of 40 pT/Hz1/2. Time-domain measurements resolved 2 nT DC magnetic field steps. These results demonstrate that electrodeposited CoNiP can provide stable internal magnetic biasing for compact magnetoelectric sensors operating without an external DC-bias magnet.