Charge-transfer-induced interfacial ferromagnetism in La0.7Sr0.3MnO3/NdNiO3

Abstract

Charge-transfer-induced interfacial ferromagnetism and its impact on the exchange bias effect in La 0.7 Sr 0.3 MnO 3 /NdNiO 3 correlated oxide heterostructures were investigated by soft x-ray absorption and x-ray magnetic circular dichroism spectra in a temperature range from 10 to 300 K. Besides the antiferromagnetic Ni 3+ cations which are naturally part of the NdNiO 3 layer, Ni 2+ ions are formed at the interface due to a charge-transfer mechanism involving the Mn element of the adjacent layer. They exhibit a ferromagnetic behavior due to the exchange coupling to the Mn 4+ ions in the La 0.7 Sr 0.3 MnO 3 layer. This can be seen as detrimental to the strength of the unidirectional anisotropy since a significant part of the interface does not contribute to the pinning of the ferromagnetic layer. By analyzing the line-shape changes of the x-ray absorption at the Ni L 2,3 edges, the metal-insulator transition of the NdNiO 3 layer is resolved in an element-specific manner. This phase transition is initiated at about 120 K, way above the paramagnetic to antiferromagnetic transition of the NdNiO 3 layer which measured to be 50 K. Exchange bias and enhanced coercive fields were observed after field cooling the sample through the Néel temperature of the NdNiO 3 layer. Different from La 0.7 Sr 0.3 MnO 3 /LaNiO 3 , the exchange bias observed in La 0.7 Sr 0.3 MnO 3 /NdNiO 3 is due to the antiferromagnetism of NdNiO 3 and the frustration at the interface. These results suggest that reducing the interfacial orbital hybridization may be used as a tunable parameter for the strength of the exchange bias effect in all-oxide heterostructures which exhibit a charge-transfer mechanism.

Proximity‐Induced Novel Ferromagnetism Accompanied with Resolute Metallicity in NdNiO3 Heterostructure

“…The interfacial ferromagnetism previously was explained as consequences of a charge transfer from FM layer to Ni sites. [ 26 , 30 ] However, our study shows that it can be induced in the NNO primarily by the stray field from the LSMO layer, which aligns the spins at Ni sites. We demonstrate that, in addition to strain and film thickness, the proximity layer emerges as an additional “knob” for manipulating existing and inducing novel physical properties, consequently ameliorating the phase diagram of RE NiO 3 .…”

“…Consequently, the ferromagnetism at the interface emerges by the exchange coupling between Ni2 + and Mn4 + ions. [ 26 ] Furthermore, it is also reported that interfacing the NNO layer with AF insulating (in its bulk form) NdMnO 3 layer ferromagnetic interplays between Mn and Ni ions occurs at low T. Although the charge transfer cannot be foreseen directly, the authors speculate that an epitaxial strain in NdNiO 3 /NdMnO 3 heterostructures is responsible for the different transport behavior. Dhaka et al., indeed found that a moderate compressive epitaxial strain very much alters the electronic structure and, therefore, transport properties on NNO film, primarily due to band reordering.…”

“…[27] Indeed, it was reported that both electronic and magnetic properties of NNO film in the proximity to a magnetic layer are strongly affected. [26,28] Moreover, various complex heterostructures created from NNO and other TMOs (CoFe 2 O 4 , LSMO, NdMnO 3 ) showed the emergence of interfacial ferromagnetism. [26,29,30] Therefore, it is crucial to disentangle the size effect from the interlayer charge transfer and potentially establish a link between the electronic structure (and MIT) and a magnetic ordering when the thin NNO film is magnetically perturbed.…”

“…Thin films and heterostructures of NNO offer new possibilities of altering the MIT via strain (compressive or tensile), film thickness [ 7 , 21 , 22 , 23 , 24 , 25 ] and/or interlayer charge transfer. [ 26 ] However, in addition to noticeable MIT change, the AFM ordering in NNO might also be modified solely by reducing the film thickness, similarly to the effect observed in LNO based superlattices. [ 27 ] Indeed, it was reported that both electronic and magnetic properties of NNO film in the proximity to a magnetic layer are strongly affected.…”

Perspective—Emergent Phases in Rare Earth Nickelate Heterostructure

“…97,100 ICT has been also reported at the interface of nickelates with mixed-valent manganite. [101][102][103][104] 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. 101,102 Wrobel et al investigated a series of La 2 CuO 4 /LaO/LaNiO 3 heterostructures to separate the dopant and doped layers from each other.…”