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Interlayer coupling through a dimensionality-induced magnetic state.

Gibert M, Viret M, Zubko P, Jaouen N, Tonnerre JM, Torres-Pardo A, Catalano S, Gloter A, Stéphan O, Triscone JM - Nat Commun (2016)

Bottom Line: We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers.All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3.This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices.

View Article: PubMed Central - PubMed

Affiliation: Département de Physique de la Matière Quantique, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland.

ABSTRACT
Dimensionality is known to play an important role in many compounds for which ultrathin layers can behave very differently from the bulk. This is especially true for the paramagnetic metal LaNiO3, which can become insulating and magnetic when only a few monolayers thick. We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers. For 7-monolayer-thick LaNiO3/LaMnO3 superlattices, negative and positive exchange bias, as well as antiferromagnetic interlayer coupling are observed in different temperature windows. All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3. This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices.

No MeSH data available.


Structural characterization of (111)-oriented LNO/LMO superlattices.(a) Reflectivity curve for linear vertical polarization of the lightat the Mn L3-edge at 300 K (above the Curie point of LMO)for a (LNO7/LMO7)15 heterostructureattesting its excellent structural quality. Dots are experimentalmeasurements and solid lines are fits. Inset: X-ray diffractogram for thesame sample. (b) High-angle annular dark-field scanning transmissionelectron microscope images corresponding to a(LNO5/LMO5)20 superlattice projectedonto the (10) plane. Growth direction is from bottom to top. Ni and Mn mapsand profiles obtained from EELS at the Ni L3 (green) and Mn (red)L2,3-edges revealing an interfacial structural asymmetry(indicated by rectangles of different width), that is, the LMO-on-LNOinterface is more abrupt than the LNO-on-LMO one.
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f1: Structural characterization of (111)-oriented LNO/LMO superlattices.(a) Reflectivity curve for linear vertical polarization of the lightat the Mn L3-edge at 300 K (above the Curie point of LMO)for a (LNO7/LMO7)15 heterostructureattesting its excellent structural quality. Dots are experimentalmeasurements and solid lines are fits. Inset: X-ray diffractogram for thesame sample. (b) High-angle annular dark-field scanning transmissionelectron microscope images corresponding to a(LNO5/LMO5)20 superlattice projectedonto the (10) plane. Growth direction is from bottom to top. Ni and Mn mapsand profiles obtained from EELS at the Ni L3 (green) and Mn (red)L2,3-edges revealing an interfacial structural asymmetry(indicated by rectangles of different width), that is, the LMO-on-LNOinterface is more abrupt than the LNO-on-LMO one.

Mentions: [(LNO)N/(LMO)M]Xsuperlattices, where N and M are the number of MLs in eachlayer—the metal–metal distance in the (111) direction—andX the number of repetitions of the stack, were grown on(111)-oriented STO substrates. As shown in Fig. 1a, strongsuperlattice peaks and thickness fringes are clearly observed in X-rayreflectivity, and diffraction measurements demonstrating the high quality of the(111)-oriented heterostructures investigated. The coherent epitaxial growth andthe absence of secondary phases or dislocations are confirmed by high-resolutionhigh-angle annular dark-field scanning transmission electron microscopy andelectron energy loss spectroscopy (EELS; Fig. 1b).Interestingly, throughout the superlattice structure, the two interfaces arefound not to be structurally equivalent: when LMO is deposited on LNO, a verysharp interface is obtained (roughness of one ML), whereas the LNO-on-LMOinterface is intermixed on the scale of two to three MLs (Fig.1b, right panels)28. Moreover, reducing the LNOthickness results in the loss of the metallic character observed in the thickerlayers as can be seen in Fig. 2a, where the resistivity ofthe (LNO7/LMO7)15 heterostructure displays atemperature-activated dependence in this low LNO thickness regime(t7LNO-[111]∼1.5 nm). This confirmsthat the dimensionality-induced insulating character of LNO, previously reportedin (001)-oriented structures, is also observed in (111)-LNO/LMO superlattices.Figure 2a also shows the temperature dependence of themagnetization for a (LNO7/LMO7)15 superlatticeafter cooling in +0.2 T, whereas magnetization-field loops atdifferent temperatures, acquired after both positive and negative field-coolingprocesses, are displayed in Fig. 2b. At 2 K, squarehysteresis loops shifted along the field axis are observed, consistent with thepresence of the previously reported negative EB17. Surprisingly,the EB changes sign at ∼15 K, before disappearing at ∼30 Kto give way to rounded magnetic loops with remnant magnetization that decreasesrapidly with temperature (SupplementaryFig. 1). The latter behaviour hints at some degree of AF couplingbetween the LMO layers in the heterostructures. Figure 2csummarizes the temperature evolution of the EB field HEB,defined as the offset of the hysteresis loop along the field axis. It is worthnoting that whereas negative EB occurs at low temperature for all periodicities,EB sign reversal is exclusively observed for the(LNO7/LMO7)15 superlattices. Successivemagnetic training measurements (shown in Supplementary Fig. 2) proved that the positive EB is an intrinsiceffect of the heterostructure and cannot be attributed to disorder29.


Interlayer coupling through a dimensionality-induced magnetic state.

Gibert M, Viret M, Zubko P, Jaouen N, Tonnerre JM, Torres-Pardo A, Catalano S, Gloter A, Stéphan O, Triscone JM - Nat Commun (2016)

Structural characterization of (111)-oriented LNO/LMO superlattices.(a) Reflectivity curve for linear vertical polarization of the lightat the Mn L3-edge at 300 K (above the Curie point of LMO)for a (LNO7/LMO7)15 heterostructureattesting its excellent structural quality. Dots are experimentalmeasurements and solid lines are fits. Inset: X-ray diffractogram for thesame sample. (b) High-angle annular dark-field scanning transmissionelectron microscope images corresponding to a(LNO5/LMO5)20 superlattice projectedonto the (10) plane. Growth direction is from bottom to top. Ni and Mn mapsand profiles obtained from EELS at the Ni L3 (green) and Mn (red)L2,3-edges revealing an interfacial structural asymmetry(indicated by rectangles of different width), that is, the LMO-on-LNOinterface is more abrupt than the LNO-on-LMO one.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4835538&req=5

f1: Structural characterization of (111)-oriented LNO/LMO superlattices.(a) Reflectivity curve for linear vertical polarization of the lightat the Mn L3-edge at 300 K (above the Curie point of LMO)for a (LNO7/LMO7)15 heterostructureattesting its excellent structural quality. Dots are experimentalmeasurements and solid lines are fits. Inset: X-ray diffractogram for thesame sample. (b) High-angle annular dark-field scanning transmissionelectron microscope images corresponding to a(LNO5/LMO5)20 superlattice projectedonto the (10) plane. Growth direction is from bottom to top. Ni and Mn mapsand profiles obtained from EELS at the Ni L3 (green) and Mn (red)L2,3-edges revealing an interfacial structural asymmetry(indicated by rectangles of different width), that is, the LMO-on-LNOinterface is more abrupt than the LNO-on-LMO one.
Mentions: [(LNO)N/(LMO)M]Xsuperlattices, where N and M are the number of MLs in eachlayer—the metal–metal distance in the (111) direction—andX the number of repetitions of the stack, were grown on(111)-oriented STO substrates. As shown in Fig. 1a, strongsuperlattice peaks and thickness fringes are clearly observed in X-rayreflectivity, and diffraction measurements demonstrating the high quality of the(111)-oriented heterostructures investigated. The coherent epitaxial growth andthe absence of secondary phases or dislocations are confirmed by high-resolutionhigh-angle annular dark-field scanning transmission electron microscopy andelectron energy loss spectroscopy (EELS; Fig. 1b).Interestingly, throughout the superlattice structure, the two interfaces arefound not to be structurally equivalent: when LMO is deposited on LNO, a verysharp interface is obtained (roughness of one ML), whereas the LNO-on-LMOinterface is intermixed on the scale of two to three MLs (Fig.1b, right panels)28. Moreover, reducing the LNOthickness results in the loss of the metallic character observed in the thickerlayers as can be seen in Fig. 2a, where the resistivity ofthe (LNO7/LMO7)15 heterostructure displays atemperature-activated dependence in this low LNO thickness regime(t7LNO-[111]∼1.5 nm). This confirmsthat the dimensionality-induced insulating character of LNO, previously reportedin (001)-oriented structures, is also observed in (111)-LNO/LMO superlattices.Figure 2a also shows the temperature dependence of themagnetization for a (LNO7/LMO7)15 superlatticeafter cooling in +0.2 T, whereas magnetization-field loops atdifferent temperatures, acquired after both positive and negative field-coolingprocesses, are displayed in Fig. 2b. At 2 K, squarehysteresis loops shifted along the field axis are observed, consistent with thepresence of the previously reported negative EB17. Surprisingly,the EB changes sign at ∼15 K, before disappearing at ∼30 Kto give way to rounded magnetic loops with remnant magnetization that decreasesrapidly with temperature (SupplementaryFig. 1). The latter behaviour hints at some degree of AF couplingbetween the LMO layers in the heterostructures. Figure 2csummarizes the temperature evolution of the EB field HEB,defined as the offset of the hysteresis loop along the field axis. It is worthnoting that whereas negative EB occurs at low temperature for all periodicities,EB sign reversal is exclusively observed for the(LNO7/LMO7)15 superlattices. Successivemagnetic training measurements (shown in Supplementary Fig. 2) proved that the positive EB is an intrinsiceffect of the heterostructure and cannot be attributed to disorder29.

Bottom Line: We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers.All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3.This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices.

View Article: PubMed Central - PubMed

Affiliation: Département de Physique de la Matière Quantique, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland.

ABSTRACT
Dimensionality is known to play an important role in many compounds for which ultrathin layers can behave very differently from the bulk. This is especially true for the paramagnetic metal LaNiO3, which can become insulating and magnetic when only a few monolayers thick. We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers. For 7-monolayer-thick LaNiO3/LaMnO3 superlattices, negative and positive exchange bias, as well as antiferromagnetic interlayer coupling are observed in different temperature windows. All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3. This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices.

No MeSH data available.