Alpha N'Diaye1 Ryan Snow2 Harsh Bhaktar2 Yves Idzerda2 Andreas Scholl1 Gong Chen3 Yizheng Wu4 Padraic Shafer1 Elke Arenholz1

1, Lawrence Berkeley National Lab, Berkeley, California, United States
2, Montana State University, Bozeman, Montana, United States
3, University of California, Davis, Davis, California, United States
4, Fudan University, Shanghai, , China

Magnetic phenomena are determined by delicate energy balances which determine the magnitude and orientation of magnetic moments as well as domain structures and topology. In transition metal alloys, varying composition and structural parameters allows tuning magnetic anisotropy[1], magnetic phase transitions (e. g. in FeRh)[2], chiral skyrmion structures [3], and many other magnetic characteristics. Here we are focusing on two examples: Tuning the stoichiometry in FexCoyMn1-x-y to enhance/ the magnetic moment and varying the Co layer thickness in a (Cu3MLCo3-10MLPt2ML)10 stack to engineer the transition from a chiral magnetic stripe phase to non-chiral and closure domain structures.

The average magnetic moment in binary 3d transition magnetic alloys is known/has been shown to follow the Slater Pauling Curve. A peak magnetic moment of 2.4 μB/atom is achieved for Fe70Co30.
Here we have explored the average magnetic moment of ternary alloys FexCoyMn1-x-y. Moreover, using epitaxial strain, we have locked-in a bcc crystal structure up to unexpectedly high Mn concentrations, up to 35%, whereas the bulk material converts to the non-magnetic fcc structure above ~12% Mn. [4] Using x-ray magnetic circular dichroism we determine the magnetic moment for each element for a variety of compositions covering around 80% of the ternary phase diagram and find that for some compositions the average magnetic moment collapses, whereas for others, which are unstable in bulk form, it reaches ~3.25 μB/atom, exceeding the moment of Fe70Co30.

Another intriguing example of magnetic engineering are (Cu3MLCo3-10MLPt2ML)10 multilayers with varying Co thickness. Changing the Co thickness, changes the impact of the interface induced Dzialochinsky-Moriia interaction (DMI): The interface anisotropy energy is unaltered, whereas the dipolar energy of the system and the cost of a domain wall increases. This leads to a transition from a chiral magnetic stripe phase through a non-chiral stripe phase to the formation of Néel closure domains. We follow this transition using x-ray spectroscopy and scattering, and x-ray PEEM.

These are two intriguing examples show important magnetic characteristic can be carefully engineered using compositions and layer thicknesses in 3d transition metal systems.