Enhanced magnetoelectric effect in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 multiferroic nanocomposite films with a SrRuO3 buffer layer

Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

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The interface magnetization of n-type BaTiO 3 /La 0.7 Sr 0.3 MnO 3 heterojunction is selectively probed by magnetic second-harmonic generation at 80 K. The injection of minority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from ferromagnetic to antiferromagnetic exchange coupled, while the bulk magnetization remains unchanged. We attribute the emergent interfacial antiferromagnetic interactions to weakening of the doubleexchange mechanism caused by the strong Hund's rule coupling between injected minority spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications.

Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications.

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La0.67Sr0.33MnO3 (LSMO) films were prepared on SrTiO3 single-crystal substrates by the pulsed laser deposition method. X-ray photoelectron spectra (XPS) were measured for the LSMO films as-prepared and annealed in vacuum, respectively. Multiple peak fitting for Mn 2p3/2 XPS spectra shows that Mn3+ and Mn4+ proportionally decrease on the surface of the LSMO film annealed in vacuum compared with the as-prepared film. And the saturation magnetization (Ms) slightly decreases. Analysis indicates that a small amount of Mn2+, as surface defects of LSMO films, hardly changed after vacuum annealing. The total of Mn3+, Mn4+ and the low-binding energy peak (LEP) remains unchanged before and after annealing in vacuum, which suggests that LEP should be related with Mn3+ and Mn4+ when the magnetic properties are considered.

The interfacial spin state of n-type BaTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunction and its dependence on gate voltage is investigated with magnetic second-harmonic generation at 78 K. The injection of minority spins alters the interface magnetization of La0.7Sr0.3MnO3 from ferromagnetic to antiferromagnetic exchange coupled, while the bulk magnetization remains unchanged. The emergent interfacial antiferromagnetic interactions are attributed to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The results will help promote the development of new interface-based functionalities and device concepts.