The electronic valence state of Mn in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 multiferroic heterostructures is probed by near edge x-ray absorption spectroscopy as a function of the ferroelectric polarization. We observe a temperature independent shift in the absorption edge of Mn associated with a change in valency induced by charge carrier modulation in the La0.8Sr0.2MnO3, demonstrating the electronic origin of the magnetoelectric effect. Spectroscopic, magnetic, and electric characterization shows that the large magnetoelectric response originates from a modified interfacial spin configuration, opening a new pathway to the electronic control of spin in complex oxide materials.PACS numbers: 75.70. Cn,78.70.Dm,73.90.+f,75.60.Ej,85.30.Tv,75.30.Kz,85.70.Ay Understanding how to couple the electric and magnetic order parameters in the solid state is a long-standing scientific challenge that is intimately linked to the spatial and temporal symmetries associated with charge and spin. Coupling of the order parameters is observed in many different materials, but the effect is generally weak in magnitude, even in materials that are both ferroelectric and ferromagnetic (multiferroic) [1][2][3]. Increasing the magnitude of the coupling is a fundamental problem in condensed matter physics with important implications for applications. For example, strong magnetoelectric coupling allows for the ultra-sensitive measurement of weak magnetic fields, and at smaller length scales, enables spin-based technologies by allowing the control of the spin state at the atomic scale via electric fields.In single phase multiferroics, the magnetic and ferroelectric orders often occur largely independent of each other, and as a result the magnetoelectric coupling tends to be small [2,4]. In order to overcome this intrinsic limitation in the coupling between the order parameters, artificially structured materials with enhanced magnetoelectric couplings have been engineered, where a break in time reversal and spatial symmetry occurs naturally at the interface between the different phases [3,5,6]. Moreover, the coupling mechanism can be tailored to benefit from several phenomena, including elastic [7,8], magnetic exchange bias [9][10][11], and charge-based [12] couplings. In charge-based multiferroic composites, the sensitivity of the electronic and spin state of strongly correlated oxides to charge provides enhanced coupling between magnetic and ferroelectric order parameters [12]; it often relies on charge doping of a "colossal" magnetoresistive (CMR) manganite to modulate between high and low spin states, which compete for the ground state of the system. However, the microscopic origin of this effect is still not fully understood. In particular, the nature of the effect and how the interplay between charge, spin, and valency combines to yield the large magnetoelectric response in this system remain to be addressed. In this Letter, we explore the sensitivity of x-ray absorption near edge spectroscopy (XANES) to the atomic electronic state to demons...

SrRuO 3 is an itinerant ferromagnet with T c ∼ 160 K and a 'bad metal' in the limit of k F l = O(1). While the magnetic properties of SrRuO 3 in the paramagnetic phase, near the ferromagnetic phase transition and at low temperatures are normal and consistent with its being a strong itinerant ferromagnet, the transport properties (resistivity and magnetoresistance) sharply deviate from that of good metallic ferromagnets. We conjecture that the distinct transport behaviour of SrRuO 3 is related to its being a 'bad metal' in the k F l = O(1) limit, and discuss the possible relevance of our results to the unusual transport properties of other 'bad metals' such as high-temperature superconductors.

The reflectivity of the itinerant ferromagnet SrRuO3 has been measured between 50 and 25,000 cm −1 at temperatures ranging from 40 to 300 K, and used to obtain conductivity, scattering rate, and effective mass as a function of frequency and temperature. We find that at low temperatures the conductivity falls unusually slowly as a function of frequency (proportional to 1/ω 1/2 ), and at high temperatures it even appears to increase as a function of frequency in the far-infrared limit. The data suggest that the charge dynamics of SrRuO3 are substantially different from those of Fermi-liquid metals.The occurrence of novel phenomena and new physics in correlated-electron systems is a recurring theme in condensed matter physics. d-electron based systems, in particular, present the combined intrigue of a range of dramatic phenomena, including superconductivity and itinerant ferromagnetism, and a tendency towards inscrutability, associated with the fact that key electronic states are often intermediate between the ideals of localization and itinerancy, which provide the starting points for most theory.Ruthenates constitute a class of transition-metal oxides occuring in both layered 1,2 and nearly cubic structures. Both electronic conduction and magnetic properties are associated with bands involving Ru-4d orbitals hybridized with O-2p levels, which manifest a range of phenomena including superconductivity and magnetism. For SrRuO 3 , which exhibits a transition from a paramagnetic to a ferromagnetic state at T c ≈ 150 K, bandstructure calculations are able to reproduce basic aspects of the magnetic behavior 3-6 . Specific heat and photoemission studies 4,7 , however, produce results for density of states and bandwidth that differ from band theory in manner that indicates the importance of electron correlation effects. In addition, transport studies 4,[8][9][10]

This review outlines developments in the growth of crystalline oxides on the ubiquitous silicon semiconductor platform. The overall goal of this endeavor is the integration of multifunctional complex oxides with advanced semiconductor technology. Oxide epitaxy in materials systems achieved through conventional deposition techniques is described first, followed by a description of the science and technology of using atomic layer-by-layer deposition with molecular beam epitaxy (MBE) to systematically construct the oxide-silicon interface. An interdisciplinary approach involving MBE, advanced real-space structural characterization, and first-principles theory has led to a detailed understanding of the process by which the interface between crystalline oxides and silicon forms, the resulting structure of the interface, and the link between structure and functionality. Potential applications in electronics and photonics are also discussed.

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