Enhanced Magnetic Order and Reversed Magnetization Induced by Strong Antiferromagnetic Coupling at Hybrid Ferromagnetic-Organic Heterojunctions.

Organic-molecular magnets based on a metal-organic framework with chemically tuned electronic and magnetic properties have been attracting tremendous attention due to their promising applications in molecular magnetic sensors, magnetic particle medicines, molecular spintronics, etc. Here, we investigated the magnetic behavior of a heterojunction comprising a ferromagnetic nickel (Ni) film and an organic semiconductor (OSC) 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) layer. Through the magneto-optical Kerr effect (MOKE), a photoemission electron microscopy (PEEM), X-ray magnetic circular dichroism (XMCD), and X-ray photoelectron spectroscopy (XPS), we found that the adsorption of F4-TCNQ on Cu(100)/Ni not only reverses the in-plane magnetization direction originally exhibited by the Ni layer but also results in enhanced magnetic ordering. Furthermore, the cyano group (CN) in adsorbed F4-TCNQ was found spin-polarized along with conspicuous charge transfer with Ni. The density functional theory (DFT) calculations suggest that the experimentally found spin polarization originates from hybridization between the CN group's π orbitals and Ni's d band. These findings signify that the hybrid states at the organic-ferromagnet interface play a key role in tailoring the magnetic behavior of interfaces. For the case of the F4-TCNQ and Ni heterojunction reported here, interface coupling is an antiferromagnetic one.

Effect of Hole Shift on Threshold Characteristics of GaSb-Based Double-Hole Photonic-Crystal Surface-Emitting Lasers.

Photonic-crystal (PC) surface-emitting lasers (SELs) with double-hole structure in the square-lattice unit cell were fabricated on GaSb-based type-I InGaAsSb/AlGaAsSb heterostructures. The relative shift of two holes was varied within one half of the lattice period. We measured the lasing wavelengths and threshold pumping densities of 16 PC-SELs and investigated their dependence on the double-hole shift. The experimental results were compared to the simulated wavelengths and threshold gains of four band-edge modes. The measured lasing wavelength did not exhibit switching of band-edge mode; however, the calculated lowest threshold mode switched as the double-hole shift exceeded one quarter of the lattice period. The identification of band-edge lasing mode revealed that modal gain discrimination was dominated over by its mode wavelength separation.