Crystal Structure and Magnetic Properties of Al_{15 + x}Fe_{9 – x}Nd₂ (x = 0, 1) Alloy

Al_{15 + x}Fe_{9 – x}Nd₂ (x = 0, 1) are tetragonal structured crystals with space group I4/mmm (No. 139, tI26). The lattice constants of Al₁₅Fe₉Nd₂ (x = 0) are a = 8.7965(1) Å and c = 5.0572(1) Å, and the lattice constants of Al₁₆Fe₈Nd₂ (x = 1, also known as Al₈Fe₄Nd) are a = 8.8155(1) Å and c = 5.0595(1) Å. Temperature-dependent magnetic susceptibility data show that Al₁₅Fe₉Nd₂ has field-sensitive characteristics under magnetic ordering transformation at a temperature below about 200 K. Under the magnetic field of 50 Oe, the Curie temperatures T_c of Al₁₅Fe₉Nd₂ and Al₈Fe₄Nd are 317 and 489 K, respectively. In a magnetic field of 8 T, the magnetization curve of Al₁₅Fe₉Nd₂ at 2 K is close to saturation, and the maximum magnetic moment is 0.66 μ_B/f.u., the remanence is 0.42 μ_B/f.u., and H_c is 1.57 T. A small increase in Al content will result in a sharp decrease in the magnetization of Al_{15+ x}Fe_{9 – x}Nd₂ (x = 0, 1) and can significantly increase the Curie temperature of the alloy. When the external magnetic field varies from –8 to 8 T at the temperature of 2 K, the alloy at x = 0 has a greater magnetic moment, remanence and coercivity; and the maximum magnetic moment, remanence, and coercivity of both phases decrease to some extent at the temperature of 300 K. x = 0 still has a relatively large magnetic moment and remanence, while x = 1 has a larger coercivity than x = 0.