Evidence of modified ferromagnetism at a buried Permalloy/CoO interface at room temperature

We have used magnetometry and resonant soft x-ray magnetic reflectometry to determine the depth-dependent charge and magnetization density on an absolute scale across a Permalloy/CoO interface above the Néel temperature of CoO. A thin magnetic layer of $1.0\mathrm{nm}$ forms at the interface. This layer has larger magnetization density and different temperature dependence of magnetization than Permalloy.

Figure 1

(Color online) (a) Hysteresis loop of Py/CoO measured at (a) $300\mathrm{K}$ and (b) $150\mathrm{K}$ after cooling in $700\mathrm{G}$ applied magnetic field. A negative exchange bias of $1000\mathrm{G}$ is observed at $150\mathrm{K}$. (c) TEM image of the Py/CoO bilayer sample.

Figure 2

(Color online) Asymmetry ratio curves as a function of wave-vector transfer $Q_Z$ at the Ni (a) and Co (b) edge. The blue circles and red squares are the data, while the continuous lines are the fitted curves. The inset in Fig. 2a shows the experimental scattering geometry used for the measurements. The inset in Fig. 2b shows an element specific hysteresis loop at the Ni $(Q_Z=0.028{\mathrm{nm}}^{-1})$ and Co $(Q_Z=0.025{\mathrm{nm}}^{-1})$ edge, respectively.

Figure 3

(Color online) (a) Charge density profile at $\mathrm{Cu}\mathrm{K}\alpha$ (black open square), Ni (blue square), and Co (red circle) energies. (b) Detail of the charge density profile at the Py/CoO interface. Right-hand scale is the $\mathrm{Cu}\mathrm{K}\alpha$ ordinate. (c) Magnetic density profile. Green lines represent structural/chemical interfaces, whereas violet dashed lines mark the region near the Py/CoO interface that exhibits modified magnetism.

Figure 4

(Color online) (a) Room temperature hysteresis measurements for same thickness of Py deposited on Si (blue) and $\mathrm{Co}\mathrm{O}∕\mathrm{Si}$ (black dashed). Red lines indicate the magnetization value at the positive and negative saturation for Py/Si and $\mathrm{Py}∕\mathrm{Co}\mathrm{O}∕\mathrm{Si}$, respectively. (b) Temperature dependence of the $M_{\mathrm{Py}∕\mathrm{Si}}∕M_{\mathrm{Py}∕\mathrm{Co}\mathrm{O}∕\mathrm{Si}}$ ratio.

Figure 5

(Color online) Depth-dependent magnetic density profile in absolute units in a Py/CoO bilayer system. Green solid lines represent structural/chemical interfaces. The inset shows the Py/CoO interface region where the structural and magnetic features are modified. Blue solid and red dashed-dot curves represent the individual Py and CoO contribution to the net magnetization. The hatched area within violet dashed lines represents the magnetic interface between Py and CoO.