The low coercivity in MnAl alloys has become a barrier to develop high performance MnAl‐based magnets for more than five decades. Herein, a high room‐temperature coercivity of 0.59 T in MnAl disc is achieved by severe plastic deformation. The grain size of the MnAl decreases significantly when ε‐phase is transformed into τ‐phase and when the τ‐phase is severely deformed. The aging process enhances the magnetization of the deformed τ‐phase significantly and reduces the coercivity of the MnAl disc to 0.396 T. The magnetic domain structure of the severely deformed τ‐MnAl exhibits many pinning sites in the intergranular regions and within the domains, resulting in the high coercivity of the bulk samples. The deformation process produces locally oriented texture of τ‐phase. This study opens a window for development of MnAl‐based bulk magnet with high coercivity and enhanced remanence.
An epoxy-resin bonding route was used to produce composite rods of the highly magnetostrictive alloys Tb 1-x Nd x( Fe 0.8 Co 0.2)1.93 (0.20 ≤ x ≤ 0.75). The structure, spin configuration, magnetostriction and particle size are investigated by means of X-ray diffraction (XRD), a standard strain technique and scanning electron microscope (SEM). The epoxy-bonded 0–3 type and pseudo 1–3 type composites are successfully fabricated, respectively. XRD analysis shows that the easy magnetization direction (EMD) for the alloy of x = 0.20 lies along 〈111〉 axis. The magnetic curing field makes the particles align as a particulate chain and also causes the particles rotating along its EMD direction. The pseudo 1–3 type epoxy-bonded composite has a larger magnetostriction than that of the 0–3 type composite, which can be attributed to the larger magnetostriction coefficient λ111, EMD lying along 〈111〉 direction, the 〈111〉-textured orientation and the chain structure. A large saturation magnetostriction (λ0S ~ 570 ppm) is achieved for the 1–3 type epoxy/ Tb 0.35 Nd 0.65( Fe 0.8 Co 0.2)1.93 composite (about 150–250 μm, 10 kOe), which approaches 70% of its monolithic alloy. Furthermore, it only contains 27 vol.% alloy particles in the insulating epoxy matrix and performs a low magnetic anisotropy, which could make it technologically interesting for the field of Nd -containing magnetostrictive materials.
Ping‐Zhan Si et al. (article number http://doi.wiley.com/10.1002/pssb.201900356) have prepared bulk MnAl nanocrystalline alloy with a highest room‐temperature coercivity up to 0.59 T by using a high‐pressure torsion process. The severe plastic deformation process decreased the grain size of τ‐phase MnAl significantly. As a result, the coercivity of the MnAl was enhanced remarkably. This work opens a window for the development of bulk MnAl with high coercivity and enhanced remanence for applications of MnAl‐based magnets. – The cover article is part of the Special Section “Advanced Magnetic Oxides”, comprising one Feature Article and 8 Original Papers (see the Preface, article number http://doi.wiley.com/10.1002/pssb.202000058).
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