Determination Of Interface Layer Effects On Exchange Coupling Between Ferromagnetic Entities And Magnetic Hardening Of Nd-Ce-Fe-B Films With High Ce Concentration

Based on ultra-high vacuum?UHV?magnetron sputtering system,we systematically studied the influence of interlayer between nanocomposite permanent magnetic materials and the effect of the exchange coupling in ferromagnetic materials.The preparation and mechanism of high performance Nd-Ce-Fe-B permanent magnetic films were also studied in this paper.X-ray diffraction?XRD?,magnetic measurement systems?MPMS-SQUID?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,and scanning probe microscopy?SPM?were used to analyze phase composition,microstructure,grain size,magnetic properties and magnetic domain structure of the samples.The effects of different interlayer materials on the exchange coupling were studied and discussed.The high-performance Nd-Ce-Fe-B films with high Ce content was prepared and analyzed.The main results are as follows:?1?The interface layer?or interlayer?could strongly influence the magnetic properties and exchange coupling in magnetic materials.Even the nature of the exchange coupling could be modified.In particular,the interlayer plays a crucial role in regulating the ferromagnetic coupling,while it is still not fully understood in a quantitative way.In this paper,a rational design method is used to characterize the interface layer effect quantitatively.A nanocomposite hard-soft layered films Sm-Co?15 nm?/interlayer?0-4 nm?/Fe?20 nm?was chosen to study the interlayer effects.It is demonstrated that the properties of nanocomposite magnets can be effectively enhanced by adding a thin nonmagnetic interlayer.The nucleation field of soft phase H_ns is determined experimentally.Here it is used as a“detector”to quantitatively characterize and further calculate the dependence of exchange coupling on thickness of nonmagnetic Cr,Ta and rare earth-rich phase interlayers.The nature of exchange coupling between the hard and soft phases after adding a nonmagnetic interlayer is identified.The decaying behavior of ferromagnetic coupling through these interlayers is determined quantitatively for the first time.The results demonstrate the validity for determining the decaying behavior of ferromagnetic coupling through different interface materials via strategy established in the present work.It opens up new opportunities to gain insight into the mechanism comprehension and high-performance design for functional magnetic materials,such as permanent magnets,magnetic recording media,etc.?2?Partial substitution of Ce in Nd-Fe-B magnets is a feasible way to cope with the crisis of Nd and Dy in Nd-Fe-B production and reduce the cost of Nd-Fe-B magnets.In the present paper,the Nd-Ce-Fe-B films with high performance have been successfully fabricated by using an ultra high vacuum?UHV?magnetron sputtering system.High magnetic performance with a ceorcivity of 13.3 kOe,a remanence of 11.4 kGs and a maximum energy product of 29.4GMOe is obtained with the Ce substitution for 50 wt.%Nd without Dy addition.The high coercivity achieved in this work is much larger than that of previously reported Ce magnets with the same Ce concentration?5-7.7 kOe?.The phase structure,microstructure and coercivity mechanism are analyzed.The coercivity mechanism is found to be mainly dominated by nucleation.Based on the microstructure observation and coercivity mechanism analysis,the fine and well separated grains,smooth grain surface,small and less inhomogeneities should be responsible for the high coercivity.Our results demonstrate that the substitution of Ce for Nd in Nd-Fe-B magnets may provide a promising way for alleviating the criticality of Nd and Dy elements.