Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y21: Emergent Magnetism at Oxide InterfacesInvited
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Sponsoring Units: GMAG Chair: Steve May, Drexel University Room: 281-282 |
Friday, March 17, 2017 11:15AM - 11:51AM |
Y21.00001: Tailoring non-collinear magnetism in oxide heterostructures, a path to novel memory Invited Speaker: Anand Bhattacharya We report upon the discovery of a non-collinear magnetic structure in superlattices of the ferromagnetic metallic oxide La$_{\mathrm{2/3}}$Sr$_{\mathrm{1/3}}$MnO$_{\mathrm{3}}$ (LSMO) and the correlated metal LaNiO$_{\mathrm{3}}$ (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependence of the non-collinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni$^{\mathrm{2+}}$ states. Furthermore, using a combination of the anomalous Nernst effect and anisotropic magnetoresistance measurements, we are able to map out the dependence of the magnetic structure on the angle and magnitude of the applied magnetic field. We are able to switch the orientation of the nearly anti-ferromagnetically aligned LSMO layers between different angular positions using a small magnetic field, and read out the different configurations using resistive measurements. Our findings suggest a pathway to a novel memory device that combines advantageous features of both antiferromagnetic and ferromagnetic memories.$\backslash $pard[1] J. Hoffman et al., ``Oscillatory Non-collinear Magnetism Induced by Interfacial Charge Transfer in Metallic Oxide Superlattices'', \textit{Phys. Rev}. X., \textit{accepted} (2016).2] J. Hoffman et al., ``Tunable Non-collinear Antiferromagnetic Resistive Memory through Oxide Superlattice Design'' (submitted). [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:27PM |
Y21.00002: Emergent Magnetic Phenomena at Oxide Interfaces Invited Speaker: Yaohua Liu Interfaces of transition metal oxides have attracted considerable attention for both fundamentally new physics and novel functionalities. Magnetic properties at oxide interfaces can be significantly different to the bulk constituents, because the delicate balance among competing terms can be broken by many mechanisms, including proximity effect, interfacial defects, strain, broken translational symmetry and charge transfer \textit{etc}. Both instances of suppressed magnetization and emergent magnetization have been observed, which can have significant consequence on the macroscopic properties of oxide heterostructures [1]. For example, we have found that the emergent nanoscale magnetization can give rise to the spin filter effect in magnetic tunnel junctions consisting of ferromagnetic manganite and insulating cuprate, which affects the spin dependent charge transport in oxide heterostructures and thus provides a knob for engineering oxide spintronics. We have also observed that the interfacial magnetization of a ferromagnetic manganite layer greatly depends on the thickness of the capping layers, which is apparently related to the induced interfacial oxygen vacancies. This result highlights the role of defect engineering in optimizing functional oxides, which is a key theme of the advanced semiconductor technology. At last, we will show that, with an adjacent oxygen-ion-conductor layer, interfacial oxygen vacancies of a transition metal oxide can be controlled via solid state gating, paving a path toward nonvolatile electric control on interfacial magnetism. [1] Y. Liu and X. Ke, Interfacial magnetism in complex oxide heterostructures probed by neutrons and x-rays. J. Phys. Condens. Matter, 27, 373003 (2015). [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 1:03PM |
Y21.00003: Controlling Emergent Ferromagnetism at Complex Oxide Interfaces Invited Speaker: Alexander Grutter The emergence of complex magnetic ground states at ABO$_{\mathrm{3}}$ perovskite heterostructure interfaces is among the most promising routes towards highly tunable nanoscale materials for spintronic device applications. Despite recent progress, isolating and controlling the underlying mechanisms behind these emergent properties remains a highly challenging materials physics problems. In particular, generating and tuning ferromagnetism localized at the interface of two non-ferromagnetic materials is of fundamental and technological interest. An ideal model system in which to study such effects is the CaRuO$_{\mathrm{3}}$/CaMnO$_{\mathrm{3}}$ interface, where the constituent materials are paramagnetic and antiferromagnetic in the bulk, respectively. Due to small fractional charge transfer to the CaMnO$_{\mathrm{3}}$ (0.07 e$^{\mathrm{-}}$/Mn) from the CaRuO$_{\mathrm{3}}$, the interfacial Mn ions are in a canted antiferromagnetic state. The delicate balance between antiferromagnetic superexchange and ferromagnetic double exchange results in a magnetic ground state which is extremely sensitive to perturbations. We exploit this sensitivity to achieve control of the magnetic interface, tipping the balance between ferromagnetic and antiferromagnetic interactions through octahedral connectivity modification. Such connectivity effects are typically tightly confined to interfaces, but by targeting a purely interfacial emergent magnetic system, we achieve drastic alterations to the magnetic ground state. These results demonstrate the extreme sensitivity of the magnetic state to the magnitude of the charge transfer, suggesting the potential for direct electric field control. We achieve such electric field control through direct back gating of a CaRuO$_{\mathrm{3}}$/CaMnO$_{\mathrm{3}}$ bilayer. Thus, the CaRuO$_{\mathrm{3}}$/CaMnO$_{\mathrm{3}}$ system provides new insight into how charge transfer, interfacial symmetry, and electric fields may be used to control ferromagnetism at the atomic scale. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:39PM |
Y21.00004: Magnetism, spin-lattice-orbital coupling and exchange-correlation energy in oxide heterostructures: Nickelate, titanate, and ruthenate Invited Speaker: Myung-Joon Han Many interesting physical phenomena and material characteristics in transition-metal oxides (TMO) come out of the intriguing interplay between charge, spin, orbital, and lattice degrees of freedom. In the thin film and/or heterointerface form of TMO, this feature can be controlled and thus be utilized. Simultaneously, however, its detailed characteristic is more difficult to be identified experimentally. For this reason, the first-principles-based approach has been playing an important role in this field of research. In this talk, I will try to give an overview of current status of first-principles methodologies especially for the magnetism in the correlated oxide heterostructures or thin films. Nickelate, titanate, and ruthenate will be taken as representative examples to demonstrate the powerfulness of and the challenges to the current methodologies On the one hand, first-principles calculation provides the useful information, understanding and prediction which can hardly be obtained from other theoretical and experimental techniques. Nickelate-manganite superlattices (LaNiO$_{\mathrm{3}}$/LaMnO$_{\mathrm{3}}$ and LaNiO$_{\mathrm{3}}$/CaMnO$_{\mathrm{3}})$ are taken as examples. In this interface, the charge transfer can induce the ferromagnetism and it can be controlled by changing the stacking sequence and number of layers. The exchange-correlation (XC) functional dependence seems to give only quantitatively different answers in this case. On the other hand, for the other issues such as orbital polarization/order coupled with spin order, the limitation of current methodology can be critical. This point will be discussed with the case of tatinate superlattice (LaTiO$_{\mathrm{3}}$/LaAlO$_{\mathrm{3}})$. For ruthenates (SrRuO$_{\mathrm{3\thinspace }}$and Sr$_{\mathrm{2}}$RuO$_{\mathrm{4}})$, we found that the probably more fundamental issue could be involved. The unusually strong dependence on the XC functional parametrization is found to give a qualitatively different conclusion for the experimentally relevant parameter regions. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 2:15PM |
Y21.00005: Magnetic coupling through lanthanum nickelate in non-metallic (111) LaMnO$_{\mathrm{3}}$/LaNiO$_{\mathrm{3}}$ superlattices Invited Speaker: Marta Gibert Perovskite nickelates (RNiO$_{\mathrm{3}}$, R$=$rare earth), with the exception of LaNiO$_{\mathrm{3}}$, display a bandwidth-controlled metal insulator transition (MIT) and antiferromagnetic order in the low temperature phase. Tuning of the MI and N\'{e}el transitions is efficiently achieved in nickelate thin films over a wide temperature range, and even LaNiO$_{\mathrm{3}}$ films undergo a MIT as the thickness is decreased. In this reduced dimensionality regime of LaNiO$_{\mathrm{3}}$, we will also report how interface engineering can be used not only to induce a new magnetic phase in this otherwise non-magnetic material but also to generate rich and complex magnetic behavior in (111)-oriented LaNiO$_{\mathrm{3}}$/LaMnO$_{\mathrm{3}}$ heterostructures. For 7-monolayer-thick LaNiO$_{\mathrm{3}}$/LaMnO$_{\mathrm{3}}$ superlattices, the emergence of negative and positive exchange bias is observed at low temperature before the stabilization of an antiferromagnetically coupled state between the LaMnO$_{\mathrm{3}}$ layers above the blocking temperature. This behavior is explained by the onset of an antiferromagnetic spiral of (1/4, 1/4 ,1/4) wave vector in the ultrathin LaNiO$_{\mathrm{3}}$ layer, akin to that of the other bulk insulating nickelates. Influence of the degree of intermixing at the monolayer scale on the interface-driven properties will also be discussed. [Preview Abstract] |
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