Exchange bias and inverted hysteresis in monolithic oxide films by structural gradient

Saghayezhian, Mohammad; Wang, Zhen; Guo, Hangwen; Jin, Rongying; Zhu, Yimei; Zhang, Jiandi; Plummer, E. W.

doi:10.1103/physrevresearch.1.033160

“…Although this might seem contradictory with our low doping bare GGA results, the DOS spectral features (including the pseudo-bandgap value) obtained with GGA are in better agreement with experimental measurements compared to GGA + U. Furthermore, LSMO thin films grown under low oxygen pressure (on top of ) with a Sr compositional gradient, recently revealed Sr-poor regions displaying a compression of the out of plane lattice parameter along with a complex magnetic behaviour 29 . Under these growth conditions, oxygen vacancies are expected throughout the sample and according to our predictions, the occupation of the bonding defect level is favoured, thus locally reducing the lattice parameter and inducing a softening of the ferromagnetic properties.…”

Section: Discussionsupporting

confidence: 59%

Localized electronic vacancy level and its effect on the properties of doped manganites

Juan

¹

,

Pruneda

²

,

Ferrari

³

2021

Sci Rep

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Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites $$\text {La}_{(1-\text {x})} \text {Sr}_{\text {x}} \text {MnO}_{3}$$ La ( 1 - x ) Sr x MnO 3 , varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range ($$0.2\,<\,\text {x}\,<\,0.5$$ 0.2 < x < 0.5 ). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites ($$\text {x}\,\sim \,1/3$$ x ∼ 1 / 3 ), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds.

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“…Also, it has been reported for multilayer structures with topological spin textures (surface skyrmions) [23,[25][26][27]. The inverted hysteresis corresponds to the antiferromagnetic interfacial coupling between the magnetic phases [51,52,57], which provides the exchange bias field.…”

Section: Discussionmentioning

confidence: 92%

“…The width of the slanted region is increasing with temperature, so the step-like magnetization switching is shifted across the zero fields. This hysteresis loop type is known as the so called inverted hysteresis [51,52]. The magnetization loops are completely suppressed above the Curie temperature, see the linear 180 K curves in Fig.…”

Section: Resultsmentioning

confidence: 98%

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Evidence for surface spin structures from first order reversal curves in magnetic topological semimetal

Avakyants¹,

Orlova²,

Timonina³

et al. 2022

Preprint

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We study magnetization reversal and first order reversal curves for two different magnetic topological semimetals, Co3Sn2S2 and Fe3GeTe2, in a wide temperature range between 80 K and 180 K. For the magnetization hysteresis loops, we observe strong temperature dependence of the initial (low-temperature) step-like magnetization switchings, so asymmetric regions of slanted magnetization appears above 140 K. Usually, similar behavior is ascribed to appearance of the second, temperature-induced magnetic phase. However, first order reversal curve analysis shows two-phase behavior even at lowest temperatures of our experiment. While the bulk ferromagnetic phase is of high temperature dependence, the second magnetic phase demonstrates perfect temperature stability below the Curie temperature. We connect the robust second phase with the surface spin textures, which are inherent for magnetic topological semimetals, so the excellent temperature stability is due to the topological protection of the semimetal surface states. This conclusion is also supported by the characteristic bow-tie magnetic hysteresis loops.

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“…S7(a) [24]), suggesting a good chemical ordering of Ru and Ti atoms across the SL. The positions of the perovskite-oxide heterostructures [38][39][40][41]. It is known that bulk STO has no out-of-plane oxygen octahedral tilt [42,43], while bulk SRO has a θRu-O-Ru around 168° [38].…”

mentioning

confidence: 99%

Interface engineering of phase separation in SrRuO3/SrTiO3 hybrid superlattices

Cui

¹

,

Zhang

²

,

Zhai

³

et al. 2022

Phys. Rev. B

1

0

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Most of the observed electronic phase separation (EPS) phenomena in complex oxides occur in systems with chemical doping, and theories have established the strong correlation between EPS and chemical-doping induced quenched disorder. Recent experiments on fabricated oxide superlattices with exclusion of chemical disorder also confirmed that the EPS disappears in the clean systems. Thus far, the existence of EPS in strongly correlated oxides without the presence of chemical doping or chemical disorder has not been proved. Here, we have built fully chemically ordered hybrid superlattices using prototypical SrRuO3 and SrTiO3 perovskite oxides. Contrary to previous theoretical and experimental results, we observe an EPS of two magnetic phases with perpendicular and cubic magnetic anisotropies, indicating the coexisting metallic and insulating phases in the superlattices. Our results provide an alternative pathway other than the chemical doping to introduce EPS in correlated oxides and strongly suggest that EPS can exist in clean systems without the need of chemical disorder.3 Electronic phase separation (EPS) in complex oxides is often manifested by the competition between multiple phases with distinct electronic/magnetic properties [1]. This phenomenon is most prominent in superconducting cuprates and colossal magnetoresistance manganites which typically show the coexistence of metallic and insulating phases on the micron to nanometer length scales [2,3]. In most cases, EPS phenomena are induced by chemical doping through ionic replacements, interstitials, or vacancies in the parent compounds [2][3][4][5]. Occasionally, EPS appears in some oxides with no apparent chemical doping, such as CaFe3O5 and LuFe2O4; however, cation nonstoichiometry still exists in these oxides [6,7] such that they can be viewed as solid solutions of Fe 2+ and Fe 3+ . The chemical dopants inevitably distribute randomly in the lattice, leading to a quenched disorder, and the role of such randomness in phase transition has been one of the main research subjects in condensed matter physics [8,9].

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Exchange bias and inverted hysteresis in monolithic oxide films by structural gradient

Cited by 10 publications

References 47 publications

Localized electronic vacancy level and its effect on the properties of doped manganites

Localized electronic vacancy level and its effect on the properties of doped manganites

Evidence for surface spin structures from first order reversal curves in magnetic topological semimetal

Interface engineering of phase separation in SrRuO3/SrTiO3 hybrid superlattices

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