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

Abstract

The effects of substituting Zr by Hf on the structural and the magnetic properties of the nanocrystalline rapidly solidified Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18-x</sub> Hf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">82</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , orthorhombic Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , hcp Co, and cubic Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sub> phases. Microstructure analysis results showed the reduction in the percentage of the soft-magnetic phase (Co) compared to the hard-magnetic phase (Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> (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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and the saturation magnetization are (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) found to linearly increases with x (x ≤ 2), then H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> slightly increases and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> slightly decreases with increasing x. The maximum energy product (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> 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.