It is generally believed that Veselagos criterion for negative refraction cannot be fulfilled in natural materials. However, considering imaginary parts of the permittivity ({epsilon}) and permeability ({mu}) and for metals at not too high frequencie
s the general condition for negative refraction becomes extremely simple: Re({mu}) < 0 --> Re(n) < 0. Here we demonstrate experimentally that in such natural metals as pure Co and FeCo alloy the negative values of the refractive index are achieved close to the frequency of the ferromagnetic resonance. Large values of the negative refraction can be obtained at room temperature and they can easily be tuned in moderate magnetic fields.
We report a memory resistance (memristor) behavior with nonlinear current-voltage characteristics and bipolar hysteretic resistance switching in the nanocolumnar manganite (LSMO) films. The switching from a high (HRS) to a low (LRS) resistance occurs
at a bias field ~1 MV/cm. Applied electric field drops mostly at the insulating interfacial LSMO layer and couples to correlated polarons at the LSMO(111)/LSMO(111) vertical interfaces. The observed memristance behaviour has an electronic (polaronic) origin and is caused by an electric-field-controlled Jahn-Teller (JT) effect, followed by the orbital reconstruction and formation of a metastable orbitally disordered interfacial phase (LRS). Compared to the earlier reported ionic memristor in Ti-O films, an electronic (polaronic) nano-sized LSMO memristor shows an additional (re-entrant) LRS-HRS switching at higher fields because of the second minimum in the elastic energy of a JT system.
A La0.75Ca0.25MnO3-film grown by metalorganic aerosol deposition technique was investigated by scanning tunnelling microscopy and spectroscopy. A small spot was found on the surface which exhibits the expected magnetic field dependence of the tunnell
ing conductivity giving the opportunity for a local spectroscopic study of the intrinsic colossal magnetoresistance (CMR) behavior. The tunnelling conductivity is strongly enhanced in an external magnetic field of 4 T and the CMR behavior can be interpreted in terms of a redistribution of occupied electronic states torwards the Fermi energy.
An interface modification of LCMO-BTO superlattices was found to massively influence magnetic and magnetotransport properties. Moreover it determines the crystal structure of the manganite layers, changing it from orthorhombic (Pnma) for the conventi
onal superlattice (cSL), to rhombohedral (R-3c) for the modified one (mSL). While the cSL shows extremely nonlinear ac transport, the mSL is an electrically homogeneous material. The observations go beyond an oversimplified picture of dead interface layers and evidence the importance of electronic correlations at perovskite interfaces.
