Crystal structure of Zr2Co11 hard magnetic compound

The compound traditionally called Zr2Co11 was studied by X-ray diffraction and electron diffraction in various cast and rapidly solidified ZrCo5.1 specimens including a single crystal. The study reveals two crystal structures. One structure is rhombohedral with arhomb = 0.476 nm and crhomb = 2.42 nm. The other structure can be described as orthorhombic with aortho ≈ arhomb, bortho≈2arhomb3 and cortho = crhomb. It is argued that these two structures correspond to high- and low-temperature Zr2Co11 phases. When cooling the solidified alloy, grains of the low-temperature orthorhombic phase are formed inside grains of the high-temperature rhombohedral phase in accordance with the orientation relations: [0 0 1]ortho//[0 0 0 1]rhomb and [0 1 0]ortho//〈1 1¯ 0 0〉rhomb. Magnetic measurements indicate that the easy magnetization direction is parallel to [0 0 0 1]rhomb and [0 0 1]ortho. We also observed possible signs of one more, hexagonal, high-temperature Zr2Co11 phase with ahex = arhomb and chex = 2crhomb/3.