Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “multiferroics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO 3 Thin Films

Polarization-induced weak ferromagnetism (WFM) was demonstrated a few years back in LiNbO3-type compounds, MTiO3 (M = Fe, Mn, Ni). Although the coexistence of ferroelectric polarization and ferromagnetism has been demonstrated in this rare multiferroic family before, first in bulk FeTiO3, then in thin-film NiTiO3, the coupling of the two order parameters has not been confirmed Here, we report the stabilization of polar, ferromagnetic NiTiO3 by oxide epitaxy on a LiNbO3 substrate utilizing tensile strain and demonstrate the theoretically predicted coupling between its polarization and ferromagnetism by X-ray magnetic circular dichroism under applied fields. The experimentally observed direction of ferroic ordering in the film is supported by simulations using the phase-field approach. Our work validates symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and WFM in MTiO3 transition metal titanates crystallizing in the LiNbO3 structure. It also demonstrates the applicability of epitaxial strain as a viable alternative to high-pressure crystal growth to stabilize metastable materials and a valuable tuning parameter to simultaneously control two ferroic order parameters to create a multiferroic. Multiferroic NiTiO3 has potential applications in spintronics where ferroic switching is used, such as new four-stage memories and electromagnetic switches.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Multiferroic tunnel junctions and ferroelectric control of magnetic state at interface (invited)

As semiconductor devices reach ever smaller dimensions, the challenge of power dissipation and quantum effect place a serious limit on the future device scaling. Recently, a multiferroic tunnel junction (MFTJ) with a ferroelectric barrier sandwiched between two ferromagnetic electrodes has drawn enormous interest due to its potential applications not only in multi-level data storage but also in electric field controlled spintronics and nanoferronics. Here, we present our investigations on four-level resistance states, giant tunneling electroresistance (TER) due to interfacial magnetoelectric coupling, and ferroelectric control of spin polarized tunneling in MFTJs. Coexistence of large tunneling magnetoresistance and TER has been observed in manganite/(Ba, Sr)TiO{sub 3}/manganite MFTJs at low temperatures and room temperature four-resistance state devices were also obtained. To enhance the TER for potential logic operation with a magnetic memory, La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/BaTiO{sub 3}/La{sub 0.5}Ca{sub 0.5}MnO{sub 3} /La{sub 0.7}Sr{sub 0.3}MnO{sub 3} MFTJs were designed by utilizing a bilayer tunneling barrier in which BaTiO{sub 3} is ferroelectric and La{sub 0.5}Ca{sub 0.5}MnO{sub 3} is close to ferromagnetic metal to antiferromagnetic insulator phase transition. The phase transition occurs when the ferroelectric polarization is reversed, resulting in an increase of TER by two orders of magnitude. Tunneling magnetoresistance can also be controlled by the ferroelectric polarization reversal, indicating strong magnetoelectric coupling at the interface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Coupling between phonon and crystal-field excitations in multiferroic PrFe 3 ( BO 3 ) 4

Far-infrared reflection and ellipsometry measurements on multiferroic PrFe 3 ( BO 3 ) 4 and SmFe 3 ( BO 3 ) 4 single crystals were used to investigate the interaction between lattice phonons and electronic excitations associated with 4 f crystal-field transitions. A temperature-dependent interference between two types of excitations was observed in PrFe 3 ( BO 3 ) 4 in which the frequency of 4 f crystal-field electronic excitation of Pr 3 + falls into the TO-LO frequency interval of the optical phonon mode near 50 cm - 1 (1.5 THz). Experimental data were explained on the basis of a theoretical model of coupled electron-phonon modes. The fitting procedure revealed the value 14.8 cm - 1 for the electron-phonon coupling constant. This rather large value points to an essential role played by the electron-phonon interaction in the physics of multiferroics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Partial glass isosymmetry transition in multiferroic hexagonal ErMn O 3

Ferroelectric transitions of a hexagonal multiferroic, ErMnO 3 , are studied by x-ray scattering techniques. An isosymmetry transition, similar to that previously observed for YMnO 3 , approximately 300 K below the well-known ferroic transition temperature is investigated. The partial glassy behavior of the isosymmetry transition is identified by appearance of quasi-elastic scattering lines in high-energy-resolution scans. The glassy behavior is further supported by the increased interlayer decorrelation of (√3×√3)R30º ordering below the isosymmetry transition. The transition behavior is considered for possible hidden sluggish modes and two-step phase transitions theoretically predicted for the stacked triangular antiferromagnets. The in-plane azimuthal (orientational) ordering behaviors were also compared to the theoretical predictions. Coherent x-ray speckle measurements show unambiguously that the domain sizes decrease anomalously near both the isosymmetry and ferroic transitions. However, domain boundary fluctuations increase monotonically with an Arrhenius form with an activation energy of 0.54(5) eV through both transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Control of Domain Structures in Multiferroic Thin Films through Defect Engineering

Domain walls (DWs) have become an essential component in nanodevices based on ferroic thin films. The domain configuration and DW stability, however, are strongly dependent on the boundary conditions of thin films, which make it difficult to create complex ordered patterns of DWs. Here, it is shown that novel domain structures, that are otherwise unfavorable under the natural boundary conditions, can be realized by utilizing engineered nanosized structural defects as building blocks for reconfiguring DW patterns. It is directly observed that an array of charged defects, which are located within a monolayer thickness, can be intentionally introduced by slightly changing substrate temperature during the growth of multiferroic BiFeO 3 thin films. These defects are strongly coupled to the domain structures in the pretemperature-change portion of the BiFeO 3 film and can effectively change the configuration of newly grown domains due to the interaction between the polarization and the defects. Thus, two types of domain patterns are integrated into a single film without breaking the DW periodicity. The potential use of these defects for building complex patterns of conductive DWs is also demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Giant low-field magnetocaloric effect and refrigerant capacity in reduced dimensionality EuTiO 3 multiferroics

Engineering magnetic materials into a thin film form while preserving its excellent magnetocaloric response is essential in the development of miniature magnetic coolers. We demonstrate how this can be achieved in the case of EuTiO 3 - an emerging multiferroic material. Unlike conventional cases where reduced dimensionality considerably decreased the magnetic entropy change (ΔS M ) and hence the refrigerant capacity (RC), we show the large low-field enhancements of ΔS M and RC in a ~100 nm thick nanocrystalline EuTiO 3 film (ΔS M ~ 24 J kg -1 K -1 and RC = 152 J kg -1 for μ 0 ΔH = 2T) relative to its single crystal counterpart (ΔS M ~ 17 J kg -1 K -1 and RC ~ 107 J kg -1 for μ 0 ΔH = 2T). The nanocrystalline EuTiO 3 film is an excellent candidate for cryogenic magnetic refrigeration. From our study, a new approach for improving both MCE and RC in magnetic nanomaterials is proposed, which will stimulate further research on magnetocaloric thin films and related cooling devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Voltage-Controlled Sensitivity of the Spin Seebeck Effect in Pt/Y 3 Fe 5 O 12 /MgO/(PbMg 1/3 Nb 2/3 O 3 ) 0.7 (PbTiO 3 ) 0.3 Multiferroic Heterostructures

The characteristics of pure spin current from the longitudinal spin Seebeck effect are investigated at room temperature in Pt / Y 3 Fe 5 O 12 deposited on the ( Pb Mg 1 / 3 Nb 2 / 3 O 3 ) 0.7 ( Pb Ti O 3 ) 0.3 substrate, through which electrostrain can be controllably applied. The applied voltage enables the modification of magnetic anisotropy in the magnetic insulating Y 3 Fe 5 O 12 layer, and thus the sensitivity of the spin Seebeck effect at small magnetic fields, without suppressing the spin Seebeck effect and the inverse spin Hall effect. This is due to the robust intrinsic physical parameters in Pt / Y 3 Fe 5 O 12 . In conclusion, our results pave the way for the application of voltage-controlled pure spin-current devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗