Magnetism of epitaxial Tb films on W(110) studied by spin-polarized low-energy electron microscopy

Thin epitaxial films of Tb metal were grown on a clean W(110) substrate in ultrahigh vacuum and studied in situ by low-energy electron microscopy. Annealed films present magnetic contrast in spin-polarized low-energy electron microscopy. The energy dependence of the electron reflectivity was determined and a maximum value of its spin asymmetry of about 1% was measured. The magnetization direction of the Tb films is in-plane. Upon raising the temperature, no change in the domain distribution is observed, while the asymmetry in the electron reflectivity decreases when approaching the critical temperature, following a power law $\sim {(1-T/T_C)}^{\beta }$ with a critical exponent $\beta$ of 0.39.

Figure 1

(a) LEEM image of the clean W(110) surface prior to deposition.The electron energy is 5.4 eV and the field of view is 7.5 $\mu \mathrm{m}$. (b) LEEM image of the as-grown 4 ML Tb/W(110) film. The electron energy is 6.2 eV and the field of view is 7.5 $\mu \mathrm{m}$.

Figure 2

Electron reflectivity at an electron energy of 5.4 eV as a function of the Tb evaporation time on the clean W(110) surface, normalized to the value prior to deposition start. Inset: Reflected electron intensity as a function of energy for both the 4 ML Tb(0001)/W(110) film and the substrate W(110). Intensities have been normalized to their respective maximum values and there is an increase in gain by a factor of about 1.5 due to a change in the detector settings in the curve for the film at an energy of about 3 eV.

Figure 3

(a) LEEM image showing the film topography after annealing at 650 K; (b) SPLEEM image with the electron polarization direction in-plane with azimuthal angle of ${70}^{\circ }$; (c) LEEM and (d) SPLEEM images of a region containing holes due to dewetting of the substrate after annealing at 800 K, showing magnetic contrast only in the film region. The field of view is 12 $\mu \mathrm{m}$.

Figure 4

(a) LEEM image showing the film topography after annealing at 650 K; (b) composite color image combining SPLEEM images acquired with the spin polarization of the electron beam at ${87}^{\circ }$ and $-3^{\circ }$ in-plane. (c) Polar histogram of magnetization directions in the area imaged in (b). Field of view is 12 $\mu \mathrm{m}$.

Figure 5

Spin asymmetry of a 20 ML terbium film as a function of electron energy along the ${47}^{\circ }$ direction. The images correspond to the energies indicated on top of each one and have a size of 3.9 $\mu \mathrm{m}$.

Figure 6

Plot of the spin asymmetry, proportional to the sample magnetization, as a function of the temperature for a 20 ML Tb film at an electron energy of 2.9 eV along the ${47}^{\circ }$ direction. The red line is a fit to an expression proportional to ${(T_C-T)}^{\beta }$, giving $\beta =0.39$.