Magnetic Properties Enhancement of FeNi45 Soft Magnetic Composites Based on Ni0.5Zn0.5Fe2O4 Ferrite-Phosphate Insulation Layer

Abstract

Soft magnetic composites (SMCs) have found extensive application in electrical energy conversion. Enhancing the high-frequency operational efficiency and reducing the core loss of the materials are critical for improving energy conversion efficiency and minimizing energy consumption. Here, we develop a methodology to enhance the effective permeability and its frequency stability under high-frequency operation and reduce core loss, through optimized particle size distribution and improved insulation layer morphology. A Ni-Zn ferrite-phosphate coating approach is proposed. Results indicate that optimizing the particle size distribution of FeNi45 to 53-75 mu m leads to a 44.3% increase in effective permeability (f = 50 kHz) and an 82.0% reduction in core loss (f = 50 kHz, B m = 50 mT). As the serrated grain morphology and crack of the Ni-Zn ferrite layer proved insufficient for insulation, phosphoric acid with good wettability was subsequently applied over the ferrite layer, forming a continuous, complete, and dense Ni-Zn ferrite-phosphate composite insulation layer. Scanning electron microscopy analysis revealed that the phosphate effectively fills the gap and crack within the ferrite, blocking eddy current paths. With a 1 wt % phosphoric acid addition, yielding a core loss of 146.71 mW/cm3, particularly the eddy current loss decreased significantly from 386.21 mW/cm3 to 26.47 mW/cm3 (f = 50 kHz, B m = 50 mT). Concurrently, exhibited an effective permeability of 82.85 (f = 50 kHz) and a DC bias performance of 53% (f = 50 kHz, H DC = 7.96 x 103 A/m (1 Oe approximate to 79.6 A/m)). These findings provide insights and practical methodologies for optimizing coating strategies in SMCs, which is beneficial for enhancing their high-frequency working efficiency in electronic applications and reducing energy consumption.