Glass-forming Ability and Magnetic Properties of Nd_70−xFe₂₀Al₁₀Co_x Alloys

The influence of Co addition on the glass-forming ability of slowly cooled Nd_70-xFe₂₀Al₁₀Co_x alloys (0 ≤ x ≤ 10) was studied by x-ray diffraction, constant-rate heating calorimetry, and magnetic measurements. Without addition of Co, the as-cast Nd₇₀Fe₂₀Al₁₀ cylinders of 3-mm diameter show a mixture of amorphous and crystalline phases after copper mold casting. Increasing the Co content promotes amorphization, and bulk amorphous specimens can be obtained for Nd₆₀Fe₂₀Al₁₀Co₁₀. No glass transition or supercooled liquid region before crystallization was observed for the bulk Nd₆₀Fe₂₀Al₁₀Co₁₀ alloy. The bulk amorphous alloy exhibits hard magnetic behavior with a remanence (J_r) of 0.09 T, a magnetization (J₁₅₀₀) of 0.13 T, and a coercivity (H_c) of 298 kAm⁻¹. The Curie temperature for the as-cast Nd_70-xFe₂₀Al₁₀Co_x cylinders increases from 480 K for x =0 to 487 K for x = 10. The enhanced glass-forming ability for the Nd–Fe–Al-based alloys upon Co addition will be critically discussed with respect to classical nucleation theory and the formation of metastable ordered clusters upon solidification.