Emergentc-axis magnetic helix in manganite-nickelate superlattices

Abstract

The nature of the magnetic order in (La 2/3 Sr 1/3 MnO3)9/(LaNiO3)3 superlattices is investigated using x-ray resonant magnetic reflectometry. We observe a new c-axis magnetic helix state in the (LaNiO3)3 layers that had never been reported in nickelates, and which mediates the ∼ 130 • magnetic coupling between the ferromagnetic (La 2/3 Sr 1/3 MnO3)9 layers, illustrating the power of x-rays for discovering the magnetic state of complex oxide interfaces. Resonant inelastic x-ray scattering and x-ray absorption spectroscopy show that Ni-O ligand hole states from bulk LaNiO3 are mostly filled due to interfacial electron transfer from Mn, driving the Ni orbitals closer to an atomic-like 3d 8 configuration. We discuss the constraints imposed by this electronic configuration to the microscopic origin of the observed magnetic structure. The presence of a magnetic helix in (La 2/3 Sr 1/3 MnO3)9/(LaNiO3)3 is crucial for modeling the potential spintronic functionality of this system and may be important for designing emergent magnetism in novel devices in general.Interfaces between complex oxide materials exhibit remarkably rich physics driven by the interplay of various types of charge, orbital and spin couplings [1-3]. Particularly fascinating is their proven ability to host new types of emergent magnetic order that do not exist in either of the bulk constituents, representing a challenge to our understanding of electron correlations, as well as an opportunity for exploitation in spintronic devices [2-4]. In fact, complex magnetic phases are potentially common in transition metal oxide superlattices given the severe effects of interfacial symmetry breaking in localized 3d orbitals [5-9], but scrutiny over the microscopic magnetic interactions at such interfaces is often constrained by limited direct evidence of the resulting magnetic structure. Superlattices composed of manganites and nickelates are a paradigmatic venue for efforts to discover and understand emergent interface magnetism, motivated by the complex magnetic order and phase diagram of its bulk constituents [10,11]. In fact, this system harbors fascinating phenomena, such as exchange bias and interfacial electronic reconstructions [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Recently, a highly unusual magnetic coupling between ferromagnetic (LSMO) 9 layers was observed in [001]-oriented (La 2/3 Sr 1/3 MnO 3 ) 9 /(LaNiO 3 ) n [(LSMO) 9 /(LNO) n , n = 1 − 9], in which the coupling angle between (LSMO) 9 layers varies between zero and 130 • as a function of n ( Fig. 1) [21]. Despite the demonstrated ability of this system to be used as resistive memory devices [4], there is no experimental evidence for how or if the non-collinear magnetism of the (LSMO) 9 layers is mediated through (LNO) n . Such lack of information critically hampers the ability to understand the physical mechanism driving the (LSMO) 9 magnetic coupling, which consequently inhibits the design of new superlattices with optimized magnetic properties.In this work we focus on the (...

Observation of an antiferromagnetic quantum critical point in high-purity LaNiO3

“…LaNiO 3 (LNO), with the largest Re cation, is the only Re-NiO 3 nickelate that is metallic down to the lowest temperatures. LNO is a correlated metal 8 and it has long been suspected that the properties of LNO are influenced by its proximity to magnetic and structural instabilities 9,10 , perhaps even by quantum fluctuations resulting from these instabilities 11,12 . However, clear experimental evidence for the effect of quantum fluctuations at low temperatures has not been reported in LNO until now.…”

Visualizing quantum phenomena at complex oxide interfaces: An atomic view from scanning transmission electron microscopy

“…In particular, our main focus is to show the indispensability of STEM for understanding the properties of complex oxide interfaces and what needs to be improved and developed in the future. We note other techniques including synchrotronbased x-ray spectroscopies [33][34][35][36][37] (such as x-ray absorptions, x-ray linear dichroism and x-ray magnetic circular dichroism) and nonlinear optics [38][39][40] (such as second harmonic generations) are also powerful tools to study complex oxide interfaces.…”

PERSPECTIVE: Emergent phases in rare earth nickelate heterostructures

“…ICT has been also reported at the interface of nickelates with mixed-valent manganite [100][101][102][103]. Among several reports, the most notable observation is the existence of helical spin arrangements within LNO layers, containing atomic-like Ni +2 with 3d 8 electron configuration [100,101].…”