Interlayer coupling through a dimensionality-induced magnetic state

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.

Oscillatory Noncollinear Magnetism Induced by Interfacial Charge Transfer in Superlattices Composed of Metallic Oxides

“…The behavior shown in Fig. 4 is also remarkably different from that recently reported for (111)-oriented LaMnO 3 =LaNiO 3 superlattices, where noncollinear magnetism was only observed for a LNO thickness of exactly 7 unit cells [16].…”

“…In this context, interfaces between oxides that are metallic in the bulk are particularly intriguing, as the large electronic compressibility, the relatively large bare dielectric constant, and band misalignment can work in concert to create significant interfacial charge transfer over a region of several unit cells [2][3][4]. In oxides derived from correlated Mott insulators, this effect can manifest latent electronic and magnetic instabilities, leading to new collective states near the interface.While a large body of work has emerged on heterostructures that incorporate insulating complex oxides [5][6][7][8][9][10][11][12][13][14][15][16], those created exclusively with metallic oxide constituents have been far less explored [17][18][19], despite the technological importance and wide range of behaviors observed in multilayers of conventional metals. The discovery of giant magnetoresistance (GMR) [20,21] and the subsequent demonstration of a tunable collinear exchange coupling in such structures [22] opened new pathways to high-density magnetic data storage.…”

Manipulating the polar mismatch at the LaNiO3/SrTiO3 (111) interface

“…These unusual interfacial phenomena have ignited tremendous effort aimed at engineering or controlling interface properties [1,5]. An important aspect of the search for and control of interfacial properties is the orientation of the substrate [6][7][8]. A prototype example is the LaNiO 3 /LaMnO 3 superlattice in highly polar [111] direction, exhibiting an unusual coupling at the interface, which displays exchange bias between ferromagnetic LaMnO 3 and paramagnetic LaNiO 3 [9,10].…”

Positive exchange bias between permalloy and twined (101¯0)-Cr2O3 films

“…The net effect of a competition between exchange coupling and uniaxial magnetic anisotropy could lead to a positive HEB [9,10]. Besides, a positive HEB has also been observed in AFM CuMn blow its spin glass transition, which is related to the Ruderman-Kittel-Kasuya-Yosida interaction [11], in (111) oriented LaNiO3/LaMnO3 superlattice, which is associated with the antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3 [12], and in the heterostucture of Co/CoO due to interfacial pinning of the AFM spins [13].…”

“…In most cases for the FM/AFM bilayer structure, a positive cooling magnetic field gives rise to a negative HEB, the shift of the magnetization hysteresis loop toward negative magnetic fields [2]. Whilst, there have been also quite a few studies reporting a positive HEB at the interface of FM/AFM and several mechanisms have been proposed to account for the positive HEB [6][7][8][9][10][11][12]. For example, magnetic ordering of the AFM spins under large cooling magnetic fields and the antiferromagnetic coupling between FM/AFM spins could give rise to a positive HEB [6][7][8].…”