A coercivity as large as 2.4 kOe has been achieved in the Ni/NiO composite film after an annealing under a magnetic field of 10 kOe and an O_2 partial pressure of 0.001 torr.The coercivity was attributed to the strong...A coercivity as large as 2.4 kOe has been achieved in the Ni/NiO composite film after an annealing under a magnetic field of 10 kOe and an O_2 partial pressure of 0.001 torr.The coercivity was attributed to the strong exchange coupling of Ni and NiO.Small grain size of Ni and NiO was observed after the post-annealing.The enhanced coercivity is probably associated with the domain wall pinning by local energy minima,the distribution of Ni and NiO,and the domain structure in the interface of Ni/NiO generated under the presence of the magnetic field during the post-annealing.展开更多
Implementation of manganese–bismuth(MnBi)alloys as high-performance permanent magnets is a challenge for physicists and engineers because the ferromagnetic low-temperature phase(LTP)is not exclusively obtained.In thi...Implementation of manganese–bismuth(MnBi)alloys as high-performance permanent magnets is a challenge for physicists and engineers because the ferromagnetic low-temperature phase(LTP)is not exclusively obtained.In this work,melting powered by four commercial magnetrons of 2000–2500 W in a microwave furnace is demonstrated as a new route to alloy MnBi.Under an argon atmosphere,microwave heating transferred to pieces of broken Bi ingots and Mn flakes for 2 h gave rise to products of inhomogeneous composition and morphology.Scanning electron micrographs were classified into three regions according to morphology and elemental composition.Cubic-like clusters characterized as Mn precipitated over light solidified Bi-rich regions,and the MnBi phase was formed in homogeneous regions with a balanced composition between Mn and Bi.A ferromagnetic hysteresis loop was obtained in the ground powder with a coercivity of 40 kA/m.Subsequent annealing at 553 K under a pressure of 414 kPa for 12 h enhanced the MnBi phase with extended regions of balanced composition.It follows that the coercivity was increased to 60 kA/m.However,remanent magnetization was slightly reduced.This MnBi alloyed by microwave radiation can be further used in rare-earth-free magnets.展开更多
文摘A coercivity as large as 2.4 kOe has been achieved in the Ni/NiO composite film after an annealing under a magnetic field of 10 kOe and an O_2 partial pressure of 0.001 torr.The coercivity was attributed to the strong exchange coupling of Ni and NiO.Small grain size of Ni and NiO was observed after the post-annealing.The enhanced coercivity is probably associated with the domain wall pinning by local energy minima,the distribution of Ni and NiO,and the domain structure in the interface of Ni/NiO generated under the presence of the magnetic field during the post-annealing.
基金Project(ThEP-60-PIP-WU3)supported by the Thailand Center of Excellence in Physics。
文摘Implementation of manganese–bismuth(MnBi)alloys as high-performance permanent magnets is a challenge for physicists and engineers because the ferromagnetic low-temperature phase(LTP)is not exclusively obtained.In this work,melting powered by four commercial magnetrons of 2000–2500 W in a microwave furnace is demonstrated as a new route to alloy MnBi.Under an argon atmosphere,microwave heating transferred to pieces of broken Bi ingots and Mn flakes for 2 h gave rise to products of inhomogeneous composition and morphology.Scanning electron micrographs were classified into three regions according to morphology and elemental composition.Cubic-like clusters characterized as Mn precipitated over light solidified Bi-rich regions,and the MnBi phase was formed in homogeneous regions with a balanced composition between Mn and Bi.A ferromagnetic hysteresis loop was obtained in the ground powder with a coercivity of 40 kA/m.Subsequent annealing at 553 K under a pressure of 414 kPa for 12 h enhanced the MnBi phase with extended regions of balanced composition.It follows that the coercivity was increased to 60 kA/m.However,remanent magnetization was slightly reduced.This MnBi alloyed by microwave radiation can be further used in rare-earth-free magnets.
