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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.


Related in: MedlinePlus

Soft X-ray reflectivity at the Ni L2-edge for the(LNO7/LMO7)15 superlattice at 30 Kafter cooling in 0.05 T.(a) Reflectivities for circularly left (CL, blue line) and right (CR,orange line) polarized light acquired in 0.05 T. (b)Reflectivity anisotropy ratio([I(H)−I(−H)]/[I(H)+I(−H)]),obtained by reversing the sign of the 0.1 T field between eachangular step, for CL (blue dots) and CR (orange dots) polarized light, andthe corresponding fit to the model for the CL polarization (solid blackline). Vertical lines indicate ½-, first-, and second-order Braggpeaks. (c) Sketch of the proposed magnetic arrangement in (111)-LNO.The (¼,¼,¼) order is stabilized by the ferromagneticcoupling with the LMO on both sides, and the resulting interaction betweenneighbouring LMO layers through 7 MLs of LNO is antiferromagnetic.
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f4: Soft X-ray reflectivity at the Ni L2-edge for the(LNO7/LMO7)15 superlattice at 30 Kafter cooling in 0.05 T.(a) Reflectivities for circularly left (CL, blue line) and right (CR,orange line) polarized light acquired in 0.05 T. (b)Reflectivity anisotropy ratio([I(H)−I(−H)]/[I(H)+I(−H)]),obtained by reversing the sign of the 0.1 T field between eachangular step, for CL (blue dots) and CR (orange dots) polarized light, andthe corresponding fit to the model for the CL polarization (solid blackline). Vertical lines indicate ½-, first-, and second-order Braggpeaks. (c) Sketch of the proposed magnetic arrangement in (111)-LNO.The (¼,¼,¼) order is stabilized by the ferromagneticcoupling with the LMO on both sides, and the resulting interaction betweenneighbouring LMO layers through 7 MLs of LNO is antiferromagnetic.

Mentions: As previously mentioned, bulk LNO is a paramagnetic metal but it can acquire somemagnetic properties when ultrathin insulating layers are sandwiched in aheterostructure configuration111718193031323334.Specifically, a non-collinear AF order with a (¼,¼,¼)pseudocubic wave vector analogous to the one displayed by all other members ofthe perovskite nickelates family has been measured for LaAlO3/LNOsuperlattices grown along the (001) direction1130. We suggesthere that such a 4-unit-cell-period magnetic superstructure along the[111]pc direction is at the origin of the AF couplingobserved in our (111)-oriented LNO/LMO superlattices with N=7,since this particular (111)-LNO thickness would specifically favour an AFarrangement between the LMO layers as illustrated in Fig.4c. Within this model, a LNO thickness of 3 and 11 MLs should alsolead to AF coupling between LMO layers. Unfortunately, N=3superlattices are not smooth enough, whereas the N=11 ones aremetallic and do not seem to stabilize the (¼,¼,¼)antiferromagnetic structure. For the other (111)-LNO thicknesses, the couplingis expected to be either ferromagnetic or at 90°. In the latter case, anychange of chirality of the (¼,¼,¼) spin arrangements wouldactually modify the coupling from 90° to −90°. The resultingrandomness would favour a multidomain state in the LMO layers, or at leastincomplete local magnetization. This behaviour is in agreement with bothmagnetometry and reflectivity measurements of superlattices with N≠7,where no ½-order peaks have been observed (as shown in Supplementary Fig. 4). The behaviour of the7-ML-LNO superlattices has been checked in three different samples. Theinsulating character of the very thin LNO layers, along with the ferromagneticcoupling to LMO at each interface181935, contribute tostabilize the (¼,¼,¼)-magnetic superstructure, otherwisefluctuating in metallic LNO3136. The existence of aninterface-induced moment in Ni, coupled parallel to the LMO magnetization, wasindeed inferred from X-ray magnetic circular dichroism measurements in several(LNO/LMO) multilayers35, as also found in other publishedworks1819. This is expected through the effect offerromagnetic superexchange between Ni2+ andMn4+, that is, in the presence of interfacial chargetransfer between LMO and LNO, and reinforced by the slight intermixing atinterfaces. In both cases the local magnetic properties would be close to thoseof the ordered La2MnNiO6 compound37, thatis, a ferromagnetic alignment of Mn and Ni spins.


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)

Soft X-ray reflectivity at the Ni L2-edge for the(LNO7/LMO7)15 superlattice at 30 Kafter cooling in 0.05 T.(a) Reflectivities for circularly left (CL, blue line) and right (CR,orange line) polarized light acquired in 0.05 T. (b)Reflectivity anisotropy ratio([I(H)−I(−H)]/[I(H)+I(−H)]),obtained by reversing the sign of the 0.1 T field between eachangular step, for CL (blue dots) and CR (orange dots) polarized light, andthe corresponding fit to the model for the CL polarization (solid blackline). Vertical lines indicate ½-, first-, and second-order Braggpeaks. (c) Sketch of the proposed magnetic arrangement in (111)-LNO.The (¼,¼,¼) order is stabilized by the ferromagneticcoupling with the LMO on both sides, and the resulting interaction betweenneighbouring LMO layers through 7 MLs of LNO is antiferromagnetic.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Soft X-ray reflectivity at the Ni L2-edge for the(LNO7/LMO7)15 superlattice at 30 Kafter cooling in 0.05 T.(a) Reflectivities for circularly left (CL, blue line) and right (CR,orange line) polarized light acquired in 0.05 T. (b)Reflectivity anisotropy ratio([I(H)−I(−H)]/[I(H)+I(−H)]),obtained by reversing the sign of the 0.1 T field between eachangular step, for CL (blue dots) and CR (orange dots) polarized light, andthe corresponding fit to the model for the CL polarization (solid blackline). Vertical lines indicate ½-, first-, and second-order Braggpeaks. (c) Sketch of the proposed magnetic arrangement in (111)-LNO.The (¼,¼,¼) order is stabilized by the ferromagneticcoupling with the LMO on both sides, and the resulting interaction betweenneighbouring LMO layers through 7 MLs of LNO is antiferromagnetic.
Mentions: As previously mentioned, bulk LNO is a paramagnetic metal but it can acquire somemagnetic properties when ultrathin insulating layers are sandwiched in aheterostructure configuration111718193031323334.Specifically, a non-collinear AF order with a (¼,¼,¼)pseudocubic wave vector analogous to the one displayed by all other members ofthe perovskite nickelates family has been measured for LaAlO3/LNOsuperlattices grown along the (001) direction1130. We suggesthere that such a 4-unit-cell-period magnetic superstructure along the[111]pc direction is at the origin of the AF couplingobserved in our (111)-oriented LNO/LMO superlattices with N=7,since this particular (111)-LNO thickness would specifically favour an AFarrangement between the LMO layers as illustrated in Fig.4c. Within this model, a LNO thickness of 3 and 11 MLs should alsolead to AF coupling between LMO layers. Unfortunately, N=3superlattices are not smooth enough, whereas the N=11 ones aremetallic and do not seem to stabilize the (¼,¼,¼)antiferromagnetic structure. For the other (111)-LNO thicknesses, the couplingis expected to be either ferromagnetic or at 90°. In the latter case, anychange of chirality of the (¼,¼,¼) spin arrangements wouldactually modify the coupling from 90° to −90°. The resultingrandomness would favour a multidomain state in the LMO layers, or at leastincomplete local magnetization. This behaviour is in agreement with bothmagnetometry and reflectivity measurements of superlattices with N≠7,where no ½-order peaks have been observed (as shown in Supplementary Fig. 4). The behaviour of the7-ML-LNO superlattices has been checked in three different samples. Theinsulating character of the very thin LNO layers, along with the ferromagneticcoupling to LMO at each interface181935, contribute tostabilize the (¼,¼,¼)-magnetic superstructure, otherwisefluctuating in metallic LNO3136. The existence of aninterface-induced moment in Ni, coupled parallel to the LMO magnetization, wasindeed inferred from X-ray magnetic circular dichroism measurements in several(LNO/LMO) multilayers35, as also found in other publishedworks1819. This is expected through the effect offerromagnetic superexchange between Ni2+ andMn4+, that is, in the presence of interfacial chargetransfer between LMO and LNO, and reinforced by the slight intermixing atinterfaces. In both cases the local magnetic properties would be close to thoseof the ordered La2MnNiO6 compound37, thatis, a ferromagnetic alignment of Mn and Ni spins.

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.


Related in: MedlinePlus