To control the interplay among magnetic, electrical, and optical related properties of magnetic YIG heterostructures has been experimentally established by tuning the strengths of the photomagnetic and electrically induced anisotropies. Therefore, manipulations of YIG magnetic properties, such as the aforementioned, under an electric field or light modulations seem to enable the creation of less dissipative magneto-optical (MO) devices and spintronic devices. These manipulations are associated with variation in the spin-polarized density of states (DOSs) of YIG band structures. However, variation in spin DOSs during the manipulation process has been less widely explored. Energy resolved magnetic circular dichroism (MCD) spectra could provide an effective means of measuring the spin-polarized DOSs of magnetic materials. In addition, with regard to applications, the change in MCD not only reveals the change in optical polarization for the design of an MO device but also shows the change in carrier polarization widely used in spintronic-related applications.

In this work, we have demonstrated how low current densities (~10⁸ A/m²) can control and/or switch optical and carrier polarization in Pt/YIG magnetic heterostructures through the selection of proper excited energy. Due to the intrinsic characteristic of YIG spin-polarized DOSs measured by energy-resolved MCD, several intriguing physical properties have been reported for the first time:

1. The spin accumulation resulting from the spin current generated from Pt leads to current-controlled optical polarization by selecting excited energies near YIG d-d transitions.

2. Furthermore, low current densities toggle the reversible optical and carrier polarization switch, which can be achieved by selecting excited energy near the YIG–charge transfer transition.

3. Reversible switching of optical and carrier polarization without the help of magnetic field was also observed.

4. Energy-resolved MCD provides strong design-on-demand characteristics for the emerging research fields of low-dissipation electrically controlled MO and spintronics devices based on magnetic insulators.

We believe that these results will be of great impact for the development in this emergent research field.