Ferromagnetic Decagonal Mn–Al–Ge–B–Fe Quasicrystals with High Coercive Force

Abstract

A ferromagnetic decagonal phase with high coercive forces exceeding 80 kA/m (I kOe) was found to form in rapidly solidified Mn 45-X AL 25 Ge 15 B 15 fe X (x = 10 and 15 at %) alloys. The decagonal alloy containing 15 at%Fe consists of fine grains with sizes of 5 to 20 nm and has the periodic lattice spacing of 1.2 nm along the c-axis direction. Furthermore, the decagonal phase contains a high density of internal defects and the electron diffraction patterns consist of reflection spots with significant streaks along the direction in the quasilattice a-b plane. The decagonal Mn 30 AL 25 Ge 15 B 15 fe 15 alloy exhibits ferromagnetic properties of 2.89 x 10 -5 Wb m/kg for magnetization under a field of 1432 kA/m (J 1432 ), 1.38 x 10 -5 Wb m/kg for remanence (B R ), 114 kA/m for intrinsic coercive force ( i H c ), 1.4 kJ / m 3 for maximum energy product (BH) max and 620 K for Curie temperature (t c ). The high coercive force is presumably due to the formation of the nanoscale ferromagnetic decagonal grains containing a high density of phason defects. The first success of synthesizing the ferromagnetic decagonal alloy with the hard magnetic characteristics is encouraging for future progress of quasicrystalline alloys as a new type of engineering material.