On the Squareness Factor determination of Nd-Dy-Fe-B-Cu hydrogen sintered magnets

Abstract

This study examines how milling time and chemical composition affect the magnetic properties of sintered NdFeB permanent magnets. The primary objective was to correlate magnetic performance with the intrinsic characteristics of the alloy, including remanence (Br), intrinsic coercivity (iHc), squareness factor (SF), squareness ratio (SQ), and the integrated area beneath the intrinsic demagnetization curves. Hysteresis loop simulations were carried out using standard magnetic parameters and interpolation methods from the SciPy library, with graphical representations generated using Matplotlib. Samples were prepared using powder metallurgy techniques and subsequently characterised magnetically using a permeameter. The results indicated that milling time plays a critical role in determining the magnetic properties. The Nd16Fe76B8 alloy exhibited the highest remanence (1225.9±1.0 mT) and intrinsic coercivity (1012.4±2.1 kA.m-1) after 54 hours of milling, used as a reference. The Nd14.5Dy1.5Fe76Nb1B7 alloy achieved superior coercivity (1130.8±20.8 kA.m-1) at the cost of reduced remanence (1093.2±5.0 mT), underscoring the influence of dysprosium on magnetic performance. The inclusion of copper in the Nd17Fe76.5Cu1.5B5 alloy improved magnetic properties at shorter milling times but it negatively impacted the squareness factor and long-term magnetic stability. The highest squareness factor (0.95±0.04) and squareness ratio (0.97±0.04) were observed for the Nd14.5Dy1.5Fe76Nb1B7 alloy, confirming the role of dysprosium and niobium in enhancing demagnetization resistance. Microstructural characterization confirmed that prolonged milling time promotes grain homogeneity, although its effect varies depending on chemical composition. These findings highlight the importance of balancing chemical composition and processing parameters to maximize magnetic stability and performance for advanced technological applications.