Magnetic and electronic states in $({\mathrm{LaMnO}}_{3}){}_{2}({\mathrm{SrMnO}}_{3}){}_{2}$ superlattice exhibiting a large negative magnetoresistance

Magnetic and electronic states in $({LaMnO}_{3})_{2} ({SrMnO}_{3})_{2}$ superlattice exhibiting a large negative magnetoresistance

Hironori Nakao, Takaaki Sudayama, Masato Kubota, Jun Okamoto, Yuichi Yamasaki, Youichi Murakami, Hiroyuki Yamada, Akihito Sawa, and Kazuaki Iwasa

Phys. Rev. B 92, 245104 – Published 7 December 2015

Abstract

Magnetic and electronic states in $({LaMnO}_{3})_{2} ({SrMnO}_{3})_{2}$ superlattices fabricated on an $({LaAlO}_{3})_{0.3} ({SrAl}_{0.5} {Ta}_{0.5} O_{3})_{0.7}$ substrate, which exhibit a large nontrivial negative magnetoresistance (MR) effect, have been investigated. The crystal structure and the Mn valence state were determined using x-ray scattering measurements near the Mn $K$ edge. These measurements revealed that the Mn valences in the ${LaMnO}_{3}$ and ${SrMnO}_{3}$ layers are 3+ and 4+, respectively; that is, valence modulation coincides with the La/Sr stacking structure. The Mn spin structure was studied by means of resonant soft x-ray scattering at the Mn $L_{2, 3}$ edge and neutron magnetic scattering measurements. We succeeded in detecting a magnetic signal indicating ferromagnetism at the interface. Finally, we suggest that the origin of the MR is the competition between ferromagnetism at the interface and underlying antiferromagnetism.

Received 30 July 2015
Revised 31 October 2015

DOI:https://doi.org/10.1103/PhysRevB.92.245104

Authors & Affiliations

Hironori Nakao^*, Takaaki Sudayama, Masato Kubota^†, Jun Okamoto^‡, Yuichi Yamasaki^§, and Youichi Murakami

Condensed Matter Research Center and Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan

Hiroyuki Yamada and Akihito Sawa

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan

Kazuaki Iwasa

Department of Physics, Tohoku University, Sendai 980-8578, Japan

^*hironori.nakao@kek.jp
^†Present address: Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan.
^‡Present address: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
^§Present address: Department of Applied Physics and Quantum-Phase Electronics Center, The University of Tokyo, Tokyo 113-8656, Japan.

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Vol. 92, Iss. 24 — 15 December 2015

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Figure 1
(a)Temperature dependence of resistivity for L2S2 (thick lines) and L5S5 (thin lines). Measurements under magnetic fields of 0 and 7 T are indicated by solid and dashed lines, respectively. These were taken from Ref. [21]. (b) Schematic view of the crystal structure of the L2S2 superlattice. The size of the lattice distortion is magnified for clarity. Three kinds of layers, LMO, SMO, and interface, exist in the L2S2 structure. (c) Diffraction pattern of the L2S2 superlattice, indicated by the thick solid line. The reciprocal lattice unit of the lattice constant, $c = 1.548$ nm, which is four primitive cells of perovskite, is used. The model calculation is indicated by the thin solid line.
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Figure 2
Energy dependence of scattering intensities of (a) the 003, (b) 004, (c) 005, and (d) 007 reflections. See Fig. 1 regarding the intensity ratios among the reflections since the intensities are roughly scaled. Model calculations are indicated by a thick solid line (“rect” model) and a thin solid line (“no” model). See the text for the details of these models. The inset in (c) shows the schematic view of the experimental configuration. The inset in (d) shows the Mn valence states of the rect model.
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Figure 3
Anomalous scattering factors (a) $f^{'} (E)$ and (b) $f^{''} (E)$ near the Mn $K$ -edge energy, which were estimated using the simple LMO $({Mn}^{3 +})$ and SMO $({Mn}^{4 +})$ films as shown by solid and dashed lines, respectively. The inset in (b) shows the schematic view of the experimental configuration.
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Figure 4
Peak profiles for (a) 003 and (b) 002 reflections along the $h$ and $l$ directions, respectively. (c) Temperature dependence of peak intensity of the 002 reflection; the baseline is shifted to allow comparison with the magnetization data. The square of the magnetization [21] $M^{2}$ is indicated by a solid line.
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Figure 5
Magnetic structure models. (a) A-type antiferromagnetism (A-AF). The difference between the magnetic moment sizes and the canted components is magnified for clarity. (b) Interface ferromagnetism and underlying antiferromagnetism. The underlying AF is drawn in parentheses. (c) Canted-AF structure, in which the interface FM and the underlying AF are superimposed.
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Figure 6
(a) XAS spectrum of the L2S2 superlattice measured in the FY mode. The intensity at the $L_{3}$ edge is suppressed because of the self-absorption effect. (b) Energy dependence of the scattering intensities in the 001 reflection. (c) Temperature dependence of the intensity ratios between the intensity at 640.4 eV and that at 634.0 eV.
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Physical Review B

covering condensed matter and materials physics

Magnetic and electronic states in $({LaMnO}_{3})_{2} ({SrMnO}_{3})_{2}$ superlattice exhibiting a large negative magnetoresistance

Hironori Nakao, Takaaki Sudayama, Masato Kubota, Jun Okamoto, Yuichi Yamasaki, Youichi Murakami, Hiroyuki Yamada, Akihito Sawa, and Kazuaki Iwasa

Phys. Rev. B 92, 245104 – Published 7 December 2015

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Physical Review B

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Magnetic and electronic states in (LaMnO3)2(SrMnO3)2 superlattice exhibiting a large negative magnetoresistance

Hironori Nakao, Takaaki Sudayama, Masato Kubota, Jun Okamoto, Yuichi Yamasaki, Youichi Murakami, Hiroyuki Yamada, Akihito Sawa, and Kazuaki Iwasa

Phys. Rev. B 92, 245104 – Published 7 December 2015

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Magnetic and electronic states in $({LaMnO}_{3})_{2} ({SrMnO}_{3})_{2}$ superlattice exhibiting a large negative magnetoresistance