Recipe for High Moment Materials with Rare-earth and 3d Transition Metal Composites

Abstract

Materials with high volume magnetization are perpetually needed for the generation of sufficiently large magnetic fields by writer pole of magnetic hard disks, especially for achieving increased areal density in storage media. In search of suitable materials combinations for this purpose, we have employed density functional theory to predict the magnetic coupling between iron and gadolinium layers separated by one to several monolayers of 3d transition metals (Sc-Zn). We demonstrate that it is possible to find ferromagnetic coupling for many of them and in particular for the early transition metals giving rise to high moment. Cr and Mn are the only elements able to produce a significant ferromagnetic coupling for thicker spacer layers. We also present experimental results on two trilayer systems Fe/Sc/Gd and Fe/Mn/Gd. From the experiments, we confirm a ferromagnetic coupling between Fe and Gd across a 3 monolayers Sc spacer or a Mn spacer thicker than 1 monolayer. In addition, we observe a peculiar dependence of Fe/Gd magnetic coupling on the Mn spacer thickness.

A systematic study of4dand5dtransition metal mediated exchange coupling between Fe and Gd nanolaminates

“…For the non-magnetic mat erials, the heterostructure presents an oscillating behavior in the coupling between Fe and Gd due to the presence of the induced magnetic moment. For four non magnetic spacers, the magnetic coupling disappears, while in Cr and Mn the oscillating behaviour is sustained by the intrinsic magnetic moment as experimentally observed [11,21]. The oscillating behaviour, reported in figure 5, was already observed in other heterostructures with bcc Fe/Co [20,24].…”

“…In figure 3 we can observe a correlation between the energy differences and the induced magnetic moments for the phase where Fe and Gd are ferromagnetically coupled. We mention that the correlation is weaker respect to the 3d case [11]. Probably this occurs because the magnetism in 4d and 5d is less relevant respect to the 3d elements.…”

“…Instead an antiferromagn etic coupling between Fe and the interlayer strongly favors a ferromagnetic coupling between Fe and Gd. All the 3d elements follow this trend [11], while the few exceptions are the d 3 , d 6 and d 9 configurations of the 4d and 5d elements. In particular, the 4d 3 and 5d 3 are the only elements able to couple ferromagnetically at the same time with Fe and Gd.…”

“…Probably this occurs because the magnetism in 4d and 5d is less relevant respect to the 3d elements. Interlayers coupling ferromagnetically with Fe tend to couple antiferromagnetically with Gd resulting in an antiferromagnetic phase of the heterostructure as for the 3d elements [11]. Instead an antiferromagn etic coupling between Fe and the interlayer strongly favors a ferromagnetic coupling between Fe and Gd.…”

Magnetic properties of 3d, 4d, and 5d transition-metal atomic monolayers in Fe/TM/Fe sandwiches: Systematic first-principles study

“…There has also been interest in forcing ferromagnetic cou- pling in rare-earth-metal/Fe sandwiches systems using 3d elements, which allow to obtaine huge magnetic moments of the order of 10 µ B /rare-earth atom [11,12]. Furthermore, the ferromagnetic coupling in the Fe/TM/Gd sandwich system with 4d and 5d metal spacers was found to be stronger than that with 3d spacers [13].…”