Magnetic microstructure and range of critical magnetic correlations in nanocrystalline gadolinium

我们将研究内部界面（晶粒和相边界）对居里转变和纳米晶块状钆和纳米晶钆合金的磁性微结构的影响。高品质的纳米晶体块状钆样品现在可以通过惰性气体冷凝技术制备，其磁性将通过磁力测量，比热测量，中子衍射，特别是通过测量使用磁性小角中子散射低捕获同位素160钆。与磁场相关的小角中子散射结合微磁学理论是一种新的方法，它允许人们确定铁磁体的内禀相互作用参数，如交换常数，各向异性场，杂散场，和自旋失调的特征长度。通过将纳米晶钆与高各向异性的稀土金属铽合金化，我们旨在定制增加的磁各向异性，并研究其对磁相互作用的影响。此外，我们建议研究晶界化学对磁行为的影响，通过合金化纳米晶钆与钽元素，表现出强烈的界面偏析的倾向。特别是，通过改变钽界面过剩浓度，我们能够研究跨晶界的交换耦合的机制。

We will study the influence of internal interfaces (grain and phase boundaries) on the Curie transition and on the magnetic microstructure of nanocrystalline bulk gadolinium and nanocrystalline gadolinium alloys. High-quality nanocrystalline bulk gadolinium samples can now be prepared by the inert-gas condensation technique, and their magnetic properties will be investigated by means of magnetometry, specific-heat measurements, neutron diffraction, and in particular by measurements using magnetic small-angle neutron scattering on the low-capturing isotope 160gadolinium. Magneticfield dependent small-angle neutron scattering in conjunction with the theory of micromagnetics is a novel approach which allows one to determine the set of intrinsic interaction parameters of a ferromagnet such as exchange constant, anisotropy field, stray field, and a characteristic length of spin misalignment. By alloying nanocrystalline gadolinium with the highly anisotropic rare-earth metal terbium, we aim at tailoring increasing magnetic anisotropy and study its effect on the magnetic interactions. Furthermore, we propose to study the effect of grain-boundary chemistry on the magnetic behavior by alloying nanocrystalline gadolinium with the nonmagnetic element tantalum which exhibits a strong tendency to interfacial segregation. In particular, by varying the tantalum interfacial excess concentration, we are able to study the mechanism of exchange coupling across grain boundaries.