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<p class="MsoNormal"><span style="font-family:"Georgia","serif"">Please join us on Thursday, February 5<sup>th</sup> at 11:30am for the Condensed Matter Seminar presented by Yaohua Liu, Oak Ridge National Laboratory in the Smith Seminar Room (1080 PRB).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Georgia","serif"">TITLE: <b><i>“Implications of Interfacial Magnetization for Oxide Spintronics”<o:p></o:p></i></b></span></p>
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<p class="MsoNormal" style="text-align:justify"><b><i><span style="font-family:"Georgia","serif"">ABSTRACT:
</span></i></b><span style="font-family:"Georgia","serif";color:#333333;background:white">Strongly correlated oxides have attracted considerable attention because the interplay among their charge, spin, orbital, and lattice degrees of freedom can lead to a
wide variety of novel phenomena and functional properties. One example is the high spin polarization in several transition-metal perovskites and double perovskites, which is highly favored for spintronic applications. However, the physical properties are often
largely altered at oxide interfaces of interest, which are crucial for the device performance but challenging to be predicted. Thus, advanced characterizations of relevant boundary regions are generally required to uncover the underlying physics that describes
the behavior of strongly correlated electrons near oxide interfaces. I will present two cases [1, 2] where interface-sensitive neutron and x-ray techniques are used to address the structure-property relationships.<o:p></o:p></span></p>
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<span style="background:white">The first case is the high-<i>T<sub>C</sub></i> and high-spin-polarization ferrimagnetic double-perovskite Sr</span><sub>2</sub><span style="background:white">CrReO</span><sub>6</sub><span style="background:white"> (SCRO) films.
We investigated the effect of Cr/Re antisite disorder and strain on the interfacial magnetization via x-ray reflectometry and polarized neutron reflectometry. It is found that these SCRO films show a nanoscale interfacial layer with reduced magnetization at
interfaces with (LaAlO</span><sub>3</sub><span style="background:white">)</span><sub>0.3</sub><span style="background:white">(Sr</span><sub>2</sub><span style="background:white">AlTaO</span><sub>6</sub><span style="background:white">)</span><sub>0.7</sub><span style="background:white"> (LSAT)
and SrTiO</span><sub>3</sub><span style="background:white"> (STO) substrates, consistent with the antisite disorders observed previously. Strain due to the lattice mismatch does not show a strong effect on the suppression of interfacial magnetization. Furthermore,
when grown on SrCr</span><sub>0.5</sub><span style="background:white">Nb</span><sub>0.5</sub><span style="background:white">O</span><sub>3</sub><span style="background:white"> (SCNO) buffered STO, the reduced-magnetization region narrows, but is clearly wider
than the antisite disorder region at the SCRO/SCNO interface. Thus, the Cr/Re antisite disorder is not the solo mechanism for the reduced interfacial magnetization and more efforts are needed to optimize the SCRO films.<o:p></o:p></span></span></p>
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<span style="background:white">The second one is the emergent low dimensional magnetization that has recently been observed at several epitaxial oxide interfaces, which have triggered increasing efforts to explore its influence on macroscopic properties. We
have utilized magnetic tunneling junctions (MTJs) consisting of ferromagnetic manganite La</span><sub>0.7</sub><span style="background:white">Ca</span><sub>0.3</sub><span style="background:white">MnO</span><sub>3</sub><span style="background:white"> (LCMO)
and insulating cuprate PrBa</span><sub>2</sub><span style="background:white">Cu</span><sub>3</sub><span style="background:white">O</span><sub>7</sub><span style="background:white"> (PBCO) to explore its effects on the charge transport. For these MTJs, the
tunnel magnetoresistance (TMR) exhibits an anomalous decrease at low temperatures. Polarized neutron reflectometry and x-ray magnetic circular dichroism (XMCD) studies ruled out the magnetization degradation of the contacts as a cause. XMCD experiments also
found a large interface-induced Cu magnetization. Calculations within the Wentzel-Kramers-Brillouin approximation show that the anomalous temperature dependence can be attributed to the competition between the positive spin polarization of the LCMO electrodes
and the negative spin-filter effect from the interfacial Cu magnetization. This work shows that the interface-induced magnetization in layered oxide heterostructures can affect the transport properties thus provides a knob for enigneering oxide spintronics.<o:p></o:p></span></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333;background:white">This work has benefited from the use of the SNS at ORNL, APS at ANL and LANSCE at LANL, which are funded by the US-DOE, BES, Scientific
User Facilities.</span><span style="font-family:"Georgia","serif""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333"><br>
<span style="background:white">[1] Yaohua Liu, J.M. Lucy <i>et al.</i>, “Effects of Strain and Buffer Layer on the Interfacial Magnetization of Sr2CrReO6 Films Determined by Polarized Neutron Reflectometry ”, Phy. Rev. B, 90, 104416 (2014).<o:p></o:p></span></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333;background:white">[2] Yaohua Liu, F.A. Cuellar
<i>et al.</i>, “Emergent Spin Filter at a Ferromagnetic and Insulating Layered Oxide Interface”, Phys. Rev. Lett. 111, 247203 (2013).<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333;background:white">If you would like to meet with Dr. Liu, please contact me for available times.<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333;background:white">Thank you,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333;background:white">Trisch<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-family:"Georgia","serif";color:#333333;background:white">2-2778<o:p></o:p></span></p>
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