Site-specific spectroscopic measurement of spin and charge in (LuFeO3)m/(LuFe2O4)1 multiferroic superlattices

Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO3)m/(LuFe2O4)1 superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ → Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe2O4 layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.Fil: Fan, Shiyu. University of Tennessee; Estados UnidosFil: Das, Hena. Cornell University; Estados UnidosFil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Smith, Kevin. University of Tennessee; Estados UnidosFil: Mundy, Julia. Harvard University; Estados Unidos. Cornell University; Estados UnidosFil: Brooks, Charles. Cornell University; Estados UnidosFil: Holtz, Megan E.. Cornell University; Estados UnidosFil: Muller, David A.. Cornell University; Estados UnidosFil: Fennie, Craig J.. Cornell University; Estados UnidosFil: Ramesh, Ramamoorthy. Lawrence Berkeley National Laboratory; Estados Unidos. University of California at Berkeley; Estados UnidosFil: Schlom, Darrell G.. Cornell University; Estados UnidosFil: McGill, Stephen. National High Magnetic Field Laboratory; Estados UnidosFil: Musfeldt, Janice L.. University of Tennessee; Estados Unido

Realistic indirect spin interactions between magnetic impurities on a metallic Pb(110) surface

Motivated by recent experiments, here we study the indirect interactions between magnetic impurities deposited on top of a clean Pb(110) surface, induced by the underlying conduction electrons. Our approach makes use of ab initio calculations to characterize the clean Pb(110) surface and avoids self-consistency, a feature that greatly reduces the computational cost. In combination with second-order perturbation theory in the microscopic s-d exchange parameter Jsd between a magnetic adatom and the conduction electrons, we are able to systematically derive the Ruderman-Kittel-Kasuya-Yosida, the Dzyaloshinskii-Moriya, and the anisotropic tensor interactions emerging at the Pb(110) surface between magnetic impurities. The only adjustable parameter is Jsd, which is fitted to reproduce the experiments. Our results show important anisotropy effects arising both from the rectangular geometry of the (110) unit cell and from the strong Rashba spin-orbit interaction due to the broken inversion symmetry at the Pb(110) surface. In addition to Pb(110), the characterization of the indirect spin interactions described here could be extended to other realistic metallic surfaces for weakly coupled impurities and would enable us to fabricate atomic-size nanostructures with engineered interactions and on-demand magnetic properties, anticipating useful applications in nanotechnology.Fil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentin

Multiferroic properties of three-layer Aurivillius compound Bi4TiFeNbO12: A first-principles and experimental study

We present a first-principles and experimental study of the structural, ferroelectric, and magnetic properties of the potentially multiferroic three-layer Aurivillius compound Bi4TiFeNbO12. This system can be realized by inserting a BiFeO3 formula unit into the two-layer Aurivilius Bi3TiNbO9 matrix. The calculations are performed using the PBEsol exchange–correlation functional within the DFT+U framework. First we search for potential cation site preference by comparing the relative stability of different Fe, Nb and Ti arrangements. We find a preference for the Fe3＋ ions to occupy the inner site within the pseudoperovskite block. This configuration exhibits a band gap of 1.2 eV (UFe=4eV) and ferroelectric and magnetic orders. A value of 66 μC/cm2 is obtained for the spontaneous polarization, which is similar to the one obtained for Bi4Ti3O12 (BIT). The magnetic ground state of this system is characterized by a strong antiferromagnetic coupling between the Fe3＋ ions located in the central layer. By mapping to a Heisenberg model, the superexchange antiferromagnetic coupling between nearest-neighbor Fe3＋ cations is estimated to be J=53 meV. Finally, we synthesize Bi3.25La0.75TiFeNbO12 ceramics by the solid-state reaction method. Their structural, electric and magnetic properties are confronted with the theoretical predictions.Fil: Lavado, Cristian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Machado, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Stachiotti, Marcelo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin