Hf Doping Effect on Hard Magnetism of Nanocrystalline Zr$_{18\hbox{-}{\rm x}}$Hf$_{\rm x}$Co$_{82}$ Ribbons

I A Al-Omari,J E Shield,Lanping Yue,W Y Zhang,X Z Li,D J Sellmyer,R Skomski

doi:10.1109/tmag.2013.2245498

Abstract

The effects of substituting Zr by Hf on the structural and the magnetic properties of the nanocrystalline rapidly solidified Zr 18-x Hf x Co 82 ribbons (x = 0, 2, 4, and 6) have been studied. X-ray diffraction and thermomagnetic measurement results indicated that upon rapid solidification processing four magnetic phases occur: rhombohedral Zr 2 Co 11 , orthorhombic Zr 2 Co 11 , hcp Co, and cubic Zr 6 Co 23 phases. Microstructure analysis results showed the reduction in the percentage of the soft-magnetic phase (Co) compared to the hard-magnetic phase (Zr 2 Co 11 (rhombohedral)) with the increase in the Hf concentration. All the samples under investigation have ferromagnetic nature, at 4.2 K and at room temperature. The coercive force (H c ) and the saturation magnetization are (M s ) found to linearly increases with x (x ≤ 2), then H c slightly increases and M s slightly decreases with increasing x. The maximum energy product (BH) max at room temperature is found to increases with increasing x reaching a maximum value for x = 4. The magnetocrystalline anisotropy parameter of these samples are calculated to be K = 1.1 MJ/m 3 and independent of Hf concentration. The above results indicate that the replacement of Zr by Hf improves the hard-magnetic properties of this class of rear-earth-free nanocrystalline permanent magnet materials.

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