Polarity and Spin–Orbit Coupling Induced Strong Interfacial Exchange Coupling: An Asymmetric Charge Transfer in Iridate–Manganite Heterostructure

Abstract

Charge transfer is of particular importance in manipulating the interface physics in transition-metal oxide heterostructures. In this work, we have fabricated epitaxial bilayers composed of polar 3d LaMnO3 and nonpolar 5d SrIrO3. Systematic magnetic measurements reveal an unexpectedly large exchange bias effect in the bilayer, together with a dramatic enhancement of the coercivity of LaMnO3. Based on first-principles calculations and x-ray absorption spectroscopy measurements, such a strong interfacial magnetic coupling is found closely associated with the polar nature of LaMnO3 and the strong spin-orbit interaction in SrIrO3, which collectively drives an asymmetric interfacial charge transfer and leads to the emergence of an interfacial spin glass state. Our study provides new insight into the charge transfer in transition-metal oxide heterostructures and offer a novel means to tune the interfacial exchange coupling for a variety of device applications. .cn (X.Q.S) † These authors contributed equally to this work IntroductionThe synthesis of dissimilar complex oxide heterostructures is currently one of the hottest areas in the design of novel functional materials. Due to the strong interplay among charge, spin, orbital, and lattice degrees of freedom, the interface between different transition-metal oxides (TMOs) in artificially layered heterostructures exhibits many exotic physical properties that are absent in the constituent bulk materials. 1-5 Among many factors, the interfacial charge transfer has been identified as an effective knob to tune the interface physics, such as mediating the interfacial magnetic coupling in YBa2Cu3O7/La0.66Ca0.33MnO3 8,9 and La0.75Sr0.25MnO3/LaNiO3 10 heterostructures. Generally, the charge transfer can be driven by the work function differences between the contact TMOs 11 or even by their polarity discontinuity 1,[12][13][14] .The most prominent model of polarity discontinuity is the emergence of two-dimension electron gas at the interface of two band insulators: polar LaAlO3 and nonpolar SrTiO3 1,12,13 . Novel phenomena, such as the insulator-to-metal transition and magnetism emerged at the interface of such heterostructures have been reported.Therefore, by manipulating the polarity discontinuity at the interface, one can effectively modulate the interfacial physical properties of TMO heterostructures 15 . Recently, the 5d iridium oxides, in which the large spin-orbit coupling (SOC) and on-site Coulomb interaction exhibit a comparable energy scale, have attracted considerable attention due to theoretical predictions of unconventional phases like superconductivity, topological Mott insulator, and Weyl semi-metals 16-19 . But so far, only a few exotic phenomena arising from the strong interfacial coupling in perovskite SrIrO3-based heterostructures have been reported 20-24 . One typical example is the observation of ferromagnetic ground state and strong anomalous Hall effect at the interface between antiferromagnetic (AFM) SrMnO3 and paramagnetic (PM) SrIrO3 2 . Despite the nonpo...

Tunable and enhanced Rashba spin-orbit coupling in iridate-manganite heterostructures

“…In addition, X-ray photoelectron spectroscopy (XPS) measurements indicates different fraction of Mn 3+ and Mn 4+ valence states in LaMnO 3 grown at different oxygen partial pressures, this affects the spin-orbit coupling related parameters at LaMnO 3 /SrIrO 3 interface. Also, interfacial charge transfer from Ir 4+ to Mn 3+ and Mn 4+ from growth variation has not been reported at a 3d -5d interface, where as individual (Mn 3+ ) LaMnO 3 /SrIrO 3 [29] and (Mn 4+ ) SrMnO 3 /SrIrO 3 interfaces charge transfer have been reported earlier [1,28].…”

“…In our case, we have mixed-valence states with varying amount of Mn 3+ and Mn 4+ for HP-and LP-LMO-SIO samples. Further, the e g states of Mn 3+ and Mn 4+ couples with interfacial e g states of Ir 4+ to give rise to molecular orbitals with energetically lower lying bonding and upper lying antibonding levels [29]. This coupling of e g (3z 2 -r 2 bonding orbital) states at the interface promotes charge transfer from Ir 4+ to Mn 3+ and Mn 4+ states.…”

“…3a and b. In general, in hole-doped LaMnO 3 systems, the Mn ions are in a mixed trivalent (3d 4 ) and tetravalent (3d 3 ) states [29]. In the case of Mn 4+ the e g orbitals are empty and singly occupied for Mn 3+ .…”

“…Novel magnetic phases such as spin-glass and skyrmions in SrRuO 3 /SrIrO 3 superlattices were also reported [27]. The interfacial charge transfer driven phenomena like the emergence of magnetism in SrIrO 3 /SrMnO 3 superlattices [1,28] and interfacial reentrant spin/super spin-glass state has been reported recently in LaMnO 3 /SrIrO 3 bilayer [29].…”

Emergent topological states via digital (001) oxide superlattices

“…While the (001) surface is the most natural surface for a (001)-grown oxide superlattice, a (100) or (010) surface can also be obtained by either cleaving the sample or mechanically polishing the sample 91,92 . Such preparation of (100) or (010) surfaces is routinely made in transmission electron microscopy (TEM) and cross-sectional scanning tunneling microscopy (STM) measurements [93][94][95][96] . Finally, we comment on how one may separate the topological surface bands from the bulk spectrum.…”