Control of perpendicular magnetic anisotropy at the Fe/MgO interface by phthalocyanine insertion

Perpendicular magnetic anisotropy at an interface between Fe and MgO with Co-phthalocyanine (CoPc) adsorption has been investigated. We find that the CoPc adsorption at an Fe/MgO interface increases the perpendicular magnetic anisotropy energy (PMA) while maintaining the voltage-controlled magnetic anisotropy effect. By performing x-ray magnetic circular dichroism spectroscopy measurements, we reveal that the CoPc adsorption induces hole accumulation at the Fe surface. The origin of the PMA enhancement is attributed to the increased orbital magnetic moment anisotropy of the Fe atoms.

Figure 1

(a) Schematic of the film stack. (b),(c) Transmission electron microscope (TEM) images of the multilayers with 0.32 nm thick CoPc layer. (d),(e) TEM images of the multilayer with 3.2 nm thick CoPc layer.

Figure 2

(a) Schematic illustration of the measurement setup for the spin-torque ferromagnetic resonance (STFMR) with voltage-driven torque. (b) Input microwave frequency as a function of the resonant magnetic field. (c) STFMR spectra for a magnetic tunnel junction without CoPc layer [Fe(0.4 nm)/MgO)]. The black squares show resonant field for each spectrum. (d) STFMR spectra for a magnetic tunnel junction with 0.35 nm CoPc layer [Fe(0.4 nm)/CoPc(0.35 nm)/MgO]. The blue circles show resonant field for each spectrum. (e) Voltage-induced changes of the resonant magnetic field in an Fe/MgO device. (f) Voltage-induced changes of the resonant magnetic field in an Fe/CoPc(0.35 nm)/MgO device.

Figure 3

(a) Schematic illustration of the measurement setup for x-ray magnetic circular dichroism (XMCD) spectroscopy with the total electron yield method. (b) Magnetization hysteresis curves taken by measuring Fe-$L_3$ edge XMCD signals. (d) Fe-$L_{2,3}$ edge x-ray absorption spectra and (e) XMCD spectra under a magnetic field of 1.9 T with the perpendicular $\left(\theta =0^{\circ }\right)$ configuration.

Figure 4

(a) Hole number, (b) effective spin magnetic moment, and (c) orbital magnetic moment of the Fe atoms. (d) Orbital magnetic moment anisotropy of the Fe atoms.

Figure 5

Schematic of the computational model with differential charge distribution [saturated level: +0.06 (red) and −0.02 (blue) $e/\mathrm{boh}{\mathrm{r}}^3$]. The data were visualized by vesta [34].