Coercivity mechanism in Nd ₆₀ Fe ₃₀ Al ₁₀ and Nd ₆₀ Fe ₂₀ Co ₁₀ Al ₁₀ alloys

The temperature dependence of the hysteresis loops and susceptibility for the melt-spun ribbon and bulk Nd ₆₀ Fe ₃₀ Al ₁₀ and Nd ₆₀ Fe ₂₀ Co ₁₀ Al ₁₀ alloys were studied. The investigations were performed on as-cast and annealed samples. Measurements of the hysteresis loops with maximum field of μ ₀ H _max = 22 T were made between 4.2 and 300 K. The temperature dependence of the coercivity follows a law that describes hard magnetic behavior based on pinning-site inhomogeneities interacting with domain walls. A quantitative evaluation of the domain-wall width, the exchange and anisotropy constants was made. The coercivity of the alloys at room temperature depends strongly on the quenching rate and/or on the production method. The room-temperature coercivity of the alloys shows an exponential behavior with the Curie temperature. Depending on the quenching rate, the melt-spun Nd-Fe, Co-Al alloys form distinctly different nonequilibrium phases, indicating that the magnetically hard precursor may vary mainly with quenching rate.