Nanoscale suppression of magnetization at atomically assembled manganite interfaces: XMCD and XRMS measurements

Kavich, J. J.; Warusawithana, Maitri; Freeland, J. W.; Ryan, Philip; Zhai, Xiaofang; Kodama, R. H.; Eckstein, J. N.

doi:10.1103/physrevb.76.014410

Cited by 68 publications

(57 citation statements)

References 26 publications

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“…Figure 3(a) shows x-ray magnetic circular dichroism (XMCD) spectra at the Mn and Ti L edge of ½LSMO 6 =STO 2 8 at 6 K in a 1 T magnetic field, conducted at the ID08 Beamline of the European Synchrotron Radiation Facility. The Mn XMCD signal of 27% is consistent with previous studies on LSMO/STO interfaces [22]. Remarkably, a clear dichroic signal is also observed at the Ti edge demonstrating the ferromagnetic character of STO, although bulk STO is a diamagnetic band insulator.…”

supporting

confidence: 78%

Electronic and Magnetic Reconstructions inLa0.7Sr0.3MnO3/SrTiO3Heterostructures: A Case of Enhanced Interlayer Coupling Controlled by the Interface

et al. 2011

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=SrTiO 3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO 3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm. DOI: 10.1103/PhysRevLett.106.147205 PACS numbers: 75.70.Ài, 73.21.Cd, 75.47.Gk Among correlated electron systems, La 0:7 Sr 0:3 MnO 3 (LSMO) has been extensively studied as a possible source of spin-polarized electrons at room temperature [1]. The large values of tunneling magnetoresistance reported for LSMO=SrTiO 3 (STO)/LSMO tunnel junctions at a low temperature drop way below the Curie temperature of the magnetic electrodes, suggesting that a depolarization of the injected current may occur at the interface [2,3]. This effect has been attributed to deteriorated magnetic properties of the manganite layer at the interface, a so-called ''dead layer,'' the origin of which is still not well understood [4,5]. Modified electronic and orbital structures at the interface [6,7] could be at the origin of the dead layer problem. In this Letter, we examine the possibility of manipulating the spin structure of the dead layer through the orbital reconstruction at the interface.The origin of novel electronic states at the interface has been discussed in terms of the combined effect of epitaxial strain and the electronic and orbital reconstruction resulting from symmetry breaking [8][9][10]. Since in these correlated oxides spin ordering is largely determined by the orbital structure through Goodenough-Kanamori rules [11,12], the modified bonding at the interface determines its magnetic structure. This is the case for the ferromagnetic state reported to occur at the interface between nonferromagnetic LaFeO 3 and LaCrO 3 [13] and is also the origin of a ferromagnetic moment found in Cu at cuprate/manganite heterostructures [14,15] Here we show that manganite layers are magnetically coupled in LSMO/STO superlattices when the STO layer is thinner than 1 nm, which gives rise to very significant changes of magnetic and conducting properties. We have examined the electronic and magnetic structure of the LSMO/STO interface and found a magnetic moment induced at the Ti, resulting from the orbital reconstruction, which couples magnetically the LSMO layers. This finding constitutes direct evidence on how macroscopic properties of a heterostructure may be controlled by the interface orbital and spin reconstruction.Using a high-pressure pure oxygen sputtering technique, we have grown two series of ½LSMO M =STO N 8 superlattices consisting of 8 bilayers of M LSMO unit cells (u.c.) and N STO u.c., on (100) STO substrates. In the first series of samples, the LSMO thickness was fixed at M ¼ 6, thin enough to highlight the interface effects, with N STO ...

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confidence: 78%

Electronic and Magnetic Reconstructions inLa0.7Sr0.3MnO3/SrTiO3Heterostructures: A Case of Enhanced Interlayer Coupling Controlled by the Interface

et al. 2011

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“…One possible origin for the reduced TMR is the reduction of ferromagnetic ordering at the interface between the manganite and the STO. These interfacial effects have been suggested to be dominant as the LSMO layer thickness decreases, causing the magnetization and T c to degrade and the resistivity to increase, ultimately resulting in films that are insulating at all temperatures when the layer thickness decreases below a reported critical value of 7-13 unit cells (4)(5)(6)(7)(8)(9)(10)(11). This critical thickness for sustaining conductivity below T c is attributed to an inherent "dead layer" at the interface between LSMO and STO (12)(13)(14).…”

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confidence: 99%

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers

Kourkoutis

Song

Hwang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

142

123

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La 0.7 Sr 0.3 MnO 3 is a conducting ferromagnet at room temperature. Combined with thin SrTiO 3 layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La 0.7 Sr 0.3 MnO 3 ∕SrTiO 3 multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La 0.7 Sr 0.3 MnO 3 layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.electron energy loss spectroscopy | manganites | scanning transmission electron microscopy C olossal magnetoresistance, metal-insulator transitions, charge/orbital ordering, and half-metal ferromagnetism are only some of the intriguing phenomena that occur in manganites and have driven interest in the family of perovskite manganese oxides (ABO 3 perovskite structure, B site occupied by Mn) (1). With a Curie temperature (T c ) of ∼370 K, the half-metal La 0.7 Sr 0.3 MnO 3 (LSMO) has been considered a promising candidate for spintronics applications. However, although complete spin polarization in LSMO was inferred from photoemission measurements (2) and a record tunneling magnetoresistance (TMR) ratio of 1,800% was obtained at low temperature in tunnel junctions with manganite electrodes separated by a thin insulating layer of SrTiO 3 (STO) (3), the TMR decreased rapidly as the temperature increased and diminished while still far below T c . One possible origin for the reduced TMR is the reduction of ferromagnetic ordering at the interface between the manganite and the STO. These interfacial effects have been suggested to be dominant as the LSMO layer thickness decreases, causing the magnetization and T c to degrade and the resistivity to increase, ultimately resulting in films that are insulating at all temperatures when the layer thickness decreases below a reported critical value of 7-13 unit cells (4-11). This critical thickness for sustaining conductivity below T c is attributed to an inherent "dead layer" at the interface between . One origin for the reduced T c and saturation magnetization of thin LSMO films compared to the bulk is believed to be a result of spin canting at the LSMO/STO interface (6, 15). Alternatively, magnetic phase separation into ferromagnetic metallic and less-ord...

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“…In this respect experimental investigations by surface sensitive x-ray magnetic scattering of layered manganite single crystals 22 and of perovskite manganite thin films 23 have shown that the average in-plane FM ordering of the surface is significantly suppressed over a length scale of about 4 unit cells (u.c.) from the surface, even at low temperature.…”

Section: Introductionmentioning

confidence: 99%

Orbital occupation, atomic moments, and magnetic ordering at interfaces of manganite thin films

et al. 2009

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We have performed x-ray linear and circular magnetic dichroism experiments at the Mn L 2,3 -edge of the La 0.7 Sr 0.3 MnO 3 ultra thin films. Our measurements show that the antiferromagnetic (AF) insulating phase is stabilized by the interfacial rearrangement of the Mn 3d orbitals, despite the relevant magnetostriction anisotropic effect on the double-exchange ferromagnetic (FM) metallic phase. As a consequence, the Mn atomic magnetic moment orientation and how it reacts to strain differ in the FM and AF phases. In some cases a FM insulating (FMI) phase adds to the AF and FM. Its peculiar magnetic properties include in-plane magnetic anisotropy and partial release of the orbital moment quenching. Nevertheless the FMI phase appears little coupled to the other ones.

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Nanoscale suppression of magnetization at atomically assembled manganite interfaces: XMCD and XRMS measurements

Cited by 68 publications

References 26 publications

Electronic and Magnetic Reconstructions inLa0.7Sr0.3MnO3/SrTiO3Heterostructures: A Case of Enhanced Interlayer Coupling Controlled by the Interface

Electronic and Magnetic Reconstructions inLa0.7Sr0.3MnO3/SrTiO3Heterostructures: A Case of Enhanced Interlayer Coupling Controlled by the Interface

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers

Orbital occupation, atomic moments, and magnetic ordering at interfaces of manganite thin films

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