Forcing Ferromagnetic Coupling Between Rare-Earth-Metal and3dFerromagnetic Films

Abstract

Using density functional calculations, we have studied the magnetic properties of nanocomposites composed of rare-earth-metal elements in contact with 3d transition metals (Fe and Cr). We demonstrate the possibility to obtain huge magnetic moments in such nanocomposites, of order 10mu(B)/rare-earth-metal atom, with a potential to reach the maximum magnetic moment of Fe-Co alloys at the top of the so-called Slater-Pauling curve. A first experimental proof of concept is given by thin-film synthesis of Fe/Gd and Fe/Cr/Gd nanocomposites, in combination with x-ray magnetic circular dichroism.

Realizing a high magnetic moment in Gd/Cr/FeCo: The role of the rare earth

“…This then raised the possibility of an overall ferromagnetic (FM) coupling between the 3d transition magnetic metal such as Fe and the RE. This was supported by density functional theory calculations that informed the synthesis of a series of Gd/Cr/Fe multilayer systems 11 . Examination of the multilayers with X-ray magnetic circular dichroism (XMCD) measurements identified coupling as evidenced by changes in the T c of the multilayer system.…”

“…External corroboration of the observation that a parasitic fcc phase is present and so degrades functional magnetic response occurs if we revisit the microstructure of the originally proposed Gd/Cr/Fe where a more recent report clearly indicated that at the thickness (4.34nm) of Gd employed there is a similarly large fraction of the Gd fcc phase present 24 , though it is not indexed. Consequently, taking our data here along with the absence of functional data in other work 11,24 we believe that "huge magnetization" of such RE/M/FM multilayers cannot be practically realized until this paramagnetic portion can be removed from the Gd or other RE film in such multilayers.…”

“…The largest values of M S occur for Cr thickness of 0.8nm and 1.0 nm and the lowest at 1.4nm and 1.8nm. For the RE/M/FM system it is postulated that the coupling sign oscillates with FM/RE separation 11 where an odd number of monolayers of Cr (0.145nm) gives antiferromagnetic coupling and even number ferromagnetic. While we do see a modulation of saturating magnetization with varying spacer distance there is not an exact corroboration with the model.…”

“…More recently there has been the suggestion to employ the use of a metal (M) spacer layer such as Chromium to mediate the coupling 11 . This was based upon the recognition that while Fe couples AF to Cr 12 , Cr couples AF to Gd 13 .…”

Structure and magnetism of Tm atoms and monolayers on W(110)

“…Ultrathin RE magnetic films and multilayers have also attracted attention due to their ability to induce perpendicular magnetic anisotropy in adjacent transition-metal layers [11], control magnetic damping in spin valve devices [12,13], as well as fabricate materials with higher magnetization compared to transition-metal alloys [14,15].…”