Dead magnetic layers at the interface: Moment quenching through hybridization and frustration

Using spin-polarized scanning tunneling microscopy (STM) we observe a two-dimensional $c(2\times 2)$ antiferromagnetic state in a pseudomorphic Mn double layer on the W(001) surface. First-principles calculations confirm the antiferromagnetic ground state. Surprisingly, only the surface Mn layer possesses a magnetic moment while the moments of interface Mn atoms vanish. Calculated STM and spin-polarized STM images as well as local vacuum density of states are in good agreement with experiments and provide strong evidence of a dead magnetic interface layer.

Figure 1

(a) Overview scan of 1.3 AL Mn/W(001) measured with a magnetic Fe/W tip. (b) Characteristic magnetic stripe pattern of the atomically resolved Mn ML. (c) Magnetic resolution and (d) spin-averaged data measured on top of a Mn DL island. The enlarged $\left(\sqrt{2}\times \sqrt{2}\right)$ magnetic unit cell indicates AFM order. The colored arrows illustrate the magnetization directions of tip and sample, respectively. Scan parameters: (a) $U=1\mathrm{V}, I=1\mathrm{nA}$; (b) $U=10\mathrm{mV}, I=20\mathrm{nA}$; (c) $U=10\mathrm{mV}, I=3\mathrm{nA}$; (d) $U=10\mathrm{mV}, I=5\mathrm{nA}$.

Figure 2

Spin-resolved local density of states (LDOS) of the Mn double layer on W(001) in the ferromagnetic (FM, dashed lines) and $c(2\times 2)$ antiferromagnetic (AFM) state (solid lines). (a) Mn surface layer, (b) Mn interface layer, and (c) W surface layer.

Figure 3

(a) Vacuum LDOS 3 Å above the Mn double layer on W(001) in the $c(2\times 2)$ AFM state as calculated via DFT. (b) Tunneling differential conductance spectrum measured on the Mn double layer on W(001). Stabilization parameters: $U=1\mathrm{V}, I=1\mathrm{nA}$ (blue); $U=0.3\mathrm{V}, I=0.5\mathrm{nA}$ (green).

Figure 4

(a) Calculated STM image ($U=+10$ mV) of the $c(2\times 2)$ AFM Mn DL on W(001) at a distance of 3 Å above the surface. Surface and interface Mn atoms are denoted by green and blue solid circles, respectively. White crosses and dots denote the downwards and upwards pointing magnetic moments. Note that we find an out-of-plane easy magnetization direction from DFT [36]. (b) Calculated SP-STM image as in (a) assuming a tip spin polarization of 0.5. (c), (d) Cross-section plots through the spin-up and spin-down partial charge density in the energy range $[E_{\mathrm{F}},E_{\mathrm{F}}+0.01\text{eV}]$ for $y$ = 0 Å of (a). (e) Total energy and (f) magnetic moment of the Mn interface and surface layer in dependence of the distance between the Mn DL and the W(001) substrate with respect to the structurally relaxed distance. The insets show simulated SP-STM images for the three interlayer distances marked in (e).

Figure 5

(a), (b) SP-STM images of the Mn DL on W(001) with a tip magnetization which is reversed between the two images due to an uncontrolled tip switching event. Scan parameters: $U=10$ mV, $I=3$ nA. The insets in the upper right corner show the calculated SP-STM image with a tip spin polarization of $+0.5$ as in Fig. 4 and with a reversed tip spin polarization of $-0.5$. (c) Sum and (d) difference of the images of (a) and (b). Note that the defect structure in the center of the experimental image serves as a marker and that its origin is nonmagnetic.