Thickness-dependent magnetic properties of oxygen-deficient EuO

We have studied how the magnetic properties of oxygen-deficient EuO sputtered thin films vary as a function of thickness. The magnetic moment, measured by polarized neutron reflectometry, and the Curie temperature are found to decrease with reducing thickness. Our results indicate that these surface-induced effects are caused by the reduced number of nearest neighbors, band bending, and the partial depopulation of the 4$f$ states of Eu.

Figure 1

PNR data (data points) and fit (lines) for varying thickness, ${\mathit{\text{d}}}_{PNR}=2.1$, 4.4, 5.2, and 6.2 nm. Data taken at $T=5$ K with an applied magnetic field of 3 kOe. The lateral dimensions of the data points indicate the extension of the vertical and horizontal error bars.

Figure 2

$T_C\left(d\right)$/$T_C$${}^{\infty }$ of EuO${}_{1-x}$ for varying thickness, for $\mathit{\text{x}}=4\%$ (black circles). The data for $\mathit{\text{x}}=0\%$ (blue triangles and circles) is taken from Refs. 19 and20. Above 40 nm, $T_C$ for $\mathit{\text{x}}=4\%$ saturates to 140 K (normalized value of unity, data points not shown). The red curve represents Eq. (1) normalized to its value for the largest experimentally considered thickness (10 nm). The black and blue fit lines are described in the text. The inset shows the EuO${}_{0.96}$ magnetization as a function of temperature for increasing thickness, with a 50 Oe applied field. Each magnetization curve is normalized to its own value at 5 K.

Figure 3

Magnetic moment of EuO${}_{0.96}$ for varying thickness (black squares), ${\mathit{\text{t}}}_{PNR}=2.1$, 4.4, 5.2, and 6.2 nm. The 11.7 nm data point is taken from Ref. 6. Data for EuO (blue triangles) is taken from Ref. 19. The inset shows a hysteresis loop taken by SQUID at 5 K for a 2-nm EuO${}_{0.96}$ sample.