Structure and magnetic properties of melt-spun Nd₃₃(Fe_xAl)₆₇ alloys

Structural and magnetic properties of melt-spun and annealed ribbons with the compositions Nd₃₃(Fe_xAl)₆₇ (x=1,2,3 and 4) have been studied. XRD and DSC results show that an amorphous structure was formed during melt spinning with a wheel surface speed of 30m/s. Several crystalline Nd-Fe-Al phases were found after annealing. A tetragonal phase with a = 9.778 Å and c = 11.516 Å was formed in the Nd₃₃(Fe_xAl)₆₇ (x=2,3 and 4) alloys after melt-spinning and annealing at 873K. This phase is antiferromagnetic with a Néel temperature of 260 K. Metamagnetism is observed at a temperature of 140K or below. Annealing Nd₃₃(FeAl)₆₇ alloy show the formation of a hexagonal phase with lattice parameters a=5.5111Å and c=8.7448Å. The magnetic measurement show that the annealed sample exhibited a hard magnetic behavior at low temperatures with a Curie temperature of 110K and a Neel temperature of 260K and a coercivity of 529 kA/m at 4.2K. The magnetic entropy change was calculated from directly isothermal magnetic measurements. The results showed that the amorphous alloy had a relatively higher magnetocaloric effect than the annealed sample, indicating that it can be considered as a candidate for magnetic refrigeration applications.