Magnetism on the Surface of the Bulk Paramagnetic Intermetallic Compound ${\mathrm{YCo}}_2$

Using full-potential electronic structure calculations, we predict that the (111) surface of the cubic Laves phase Pauli paramagnet $\mathrm{YC}{\mathrm{o}}_2$ is ferromagnetic. The magnetism of the (111) surface is independent of the termination of the surface, does not extend beyond two Co layers, and is related to the field-induced metamagnetism of the bulk. $\mathrm{YC}{\mathrm{o}}_2$ appears to be a prominent candidate to demonstrate the phenomenon of surface-induced itinerant magnetism localized in two dimensions.

Figure 1

Structure of the cubic Laves phase (C15) compound ${\mathrm{YCo}}_2$: upper panel: bulk. Lower panels: top and side view of the Co-terminated ${\mathrm{YCo}}_2(111)$ surface. $a,b$ denote different Y and Co sites introduced by the surface.

Figure 2

Calculated magnetic moment vs applied field for bulk ${\mathrm{YCo}}_2$ at lattice constants corresponding to equilibrium nonmagnetic LDA, to experiment, to a value halfway between, and to the calculated equilibrium values determined for fixed $\mu$. The inset shows the relative free energy at constant magnetic field for $a=7.086\AA$. (Note that only comparisons of $\Delta F_H$ at the same field are meaningful.)

Figure 3

Nonmagnetic DOS for a bulk-truncated unrelaxed Co-terminated ${\mathrm{YCo}}_2(111)$ surface.