Epitaxial perovskite (110) oriented SrIrO3(SIO) thin films were grown by pulsed laser deposition on (110) oriented DyScO3(DSO) substrateswith various film thicknesst(2 nm1 increases with decreasingTand is especially pronounced for the thinnest films, whichlikewise display a hysteretic field dependence belowT∗≈3 K. The coercive fieldHcamounts to 2-5 T. Both,T∗andHcare very similar to themagnetic ordering temperature and coercivity of DSO which strongly suggests substrate-induced mechanism as a reason for the anisotropicmagnetotransport in the SIO film

Fuchs, D.

Jaiswal, A. K.

Schneider, R.

Singh, R.

Zaitsev, A. G.

English

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AIP Advances 9, 125034 (2019); https://doi.org/10.1063/1.5129350 9, 125034© 2019 Author(s).Magnetotransport of SrIrO3 films on (110)DyScO3Cite as: AIP Advances 9, 125034 (2019); https://doi.org/10.1063/1.5129350Submitted: 27 September 2019 . Accepted: 20 November 2019 . Published Online: 23 December 2019A. K. Jaiswal, A. G. Zaitsev, R. Singh, R. Schneider, and D. FuchsCOLLECTIONSPaper published as part of the special topic on 64th Annual Conference on Magnetism and Magnetic MaterialsNote: This paper was presented at the 64th Annual Conference on Magnetism and Magnetic Materials.ARTICLES YOU MAY BE INTERESTED INSuppression of twinning and enhanced electronic anisotropy of SrIrO3 filmsApplied Physics Letters 115, 031904 (2019); https://doi.org/10.1063/1.5110982Strain-engineering of charge transport in the correlated Dirac semimetal of perovskiteCaIrO3 thin filmsAPL Materials 7, 081115 (2019); https://doi.org/10.1063/1.5109582Tuning the superconducting transition of SrTiO3-based 2DEGs with lightApplied Physics Letters 115, 122601 (2019); https://doi.org/10.1063/1.5119417AIP Advances ARTICLE scitation.org/journal/advMagnetotransport of SrIrO3 films on (110) DyScO3Cite as: AIP Advances 9, 125034 (2019); doi: 10.1063/1.5129350Presented: 5 November 2019 • Submitted: 27 September 2019 •Accepted: 20 November 2019 • Published Online: 23 December 2019A. K. Jaiswal,1,2 A. G. Zaitsev,1 R. Singh,2 R. Schneider,1 and D. Fuchs1,a)AFFILIATIONS1 Institute for Solid-State Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany2Department of Physics, Indian Institute of Technology Delhi, 110016 New Delhi, IndiaNote: This paper was presented at the 64th Annual Conference on Magnetism and Magnetic Materials.a)Corresponding author: dirk.fuchs@kit.eduABSTRACTEpitaxial perovskite (110) oriented SrIrO3 (SIO) thin films were grown by pulsed laser deposition on (110) oriented DyScO3 (DSO) substrateswith various film thickness t (2 nm < t < 50 nm). All the films were produced with stoichiometric composition, orthorhombic phase, and withhigh crystallinity. The nearly perfect in-plane lattice matching of DSO with respect to SIO and same symmetry result in a full epitaxial in-planealignment, i.e., the c-axis of DSO and SIO are parallel to each other with only slightly enlarged d110 out-of-plane lattice spacing (+0.38%) due tothe small in-plane compressive strain caused by the DSO substrate. Measurements of the magnetoresistance MR were carried out for currentflow along the [001] and [1-10] direction of SIO and magnetic field perpendicular to the film plane. MR appears to be distinctly differentfor both directions. The anisotropy MR001/MR1-10 > 1 increases with decreasing T and is especially pronounced for the thinnest films, whichlikewise display a hysteretic field dependence below T∗ ≈ 3 K. The coercive field Hc amounts to 2-5 T. Both, T∗ and Hc are very similar to themagnetic ordering temperature and coercivity of DSO which strongly suggests substrate-induced mechanism as a reason for the anisotropicmagnetotransport in the SIO films.© 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/1.5129350., sI. INTRODUCTIONQuantum materials with competing strength of various interac-tions have gained increasing interests in recent years due to their richphase diagram and possible application of realizing new quantumstates.1,2 Iridium based 5d-transition metal oxides (TMOs) displaylarge spin-orbit coupling (SOC) compared to 3d- & 4d- TMOs dueto the heavy Ir with atomic number Z = 77 (SOC ∝ Z4).3 The deli-cate interplay of spin-orbit coupling, electron correlations, and crys-tal field energy makes iridates a prototype system to explore exoticphases originating from the competition of these interactions.4–14Dimensionality controlled physical properties have beenobserved in the Ruddlesden-Popper (RP) family of strontium iri-dates (Srn+1IrnO3n+1 ≡ SrO(SrIrO3)n) where n layers of SrIrO3 areintercalated between SrO layers along the c-axis direction.15 The endmember SrIrO3 (n = ∞) has a semimetallic paramagnetic ground-state. An increase of n results in an increase of hybridization of Ir5d and O 2p orbitals which consequently pushes SrIrO3 (SIO) to asemimetallic state.16 Thus, SIO is very close to a metal-to-insulatortransition and magnetic order. Therefore, the properties of SIO areexpected to be susceptible to external perturbations.At ambient pressure, the monoclinic phase C2/2 (15) of SIO isenergetically favorable while orthorhombic perovskite phase Pbnm(62) requires synthesis under high pressure (p ≈ 40 kbar). How-ever, it is possible to stabilize the orthorhombic phase at ambientpressure using thin-film growth technology. Recently, people havesuccessfully grown thin films of SIO on various lattice-matchedsubstrates.17–19 Growth conditions, underlying substrate, and filmthickness have a profound effect on the electronic properties of SIOfilms.16,20 A metal-to-insulator transition (MIT) has been observedfor SIO films with thickness t ≤ 3-unit cells on SrTiO3 (001) wheresuppression of in-plane octahedral rotation opens a charge gap at theFermi level.21 In literature, there are few reports of magnetic order-ing in SIO based interfaces and superlattices.22,23 For [(SrIrO3)m,SrTiO3] (m = 1,2,3 and ∞) superlattices, where m is the numberof SIO unit cells, a semimetal to insulator and magnetic phase tran-sition has been observed simultaneously, for m ≈ 3, indicating thecorrelation between charge gap and magnetic ordering.22In this study, we report on the magnetotransport of SIO filmson DSO (110) substrates for various film thickness t. Magnetoresis-tance MR is positive and shows sharp cusp at lower fields hinting toSOC-induced weak-antilocalization. MR displays different behaviorAIP Advances 9, 125034 (2019); doi: 10.1063/1.5129350 9, 125034-1© Author(s) 2019AIP Advances ARTICLE scitation.org/journal/advalong the [001] and [1-10] direction. In contrast to films with t ≥9 nm, SIO film with t = 2.3 nm show a hysteretic behavior belowT∗ ≈ 3 K. The measurements hint to a substrate-induced magneticorder in the SIO film.II. EXPERIMENTAL(110) oriented perovskite SIO films were grown on DyScO3(110) substrates (5×5 mm2 from CrysTec GmbH) with various filmthickness t (2nm < t < 50 nm) using a pulsed laser deposition sys-tem with a KrF excimer laser (λ = 248 nm). Details on film growthare described elsewhere.24 A capping layer of STO (∼4 nm) wasdeposited in situ to protect and prevent the SIO film surfaces fromany possible degradation. Structural properties of the films such asfilm thicknesses t, roughness r, crystallinity and out of plane latticespacing d110 were analyzed by x-ray reflectivity (XRR) and diffrac-tion (XRD) measurements using a four-circle diffractometer (BrukerD8 Discover). Stoichiometric film composition was confirmed byRutherford backscattering spectrometry.To study electronic transport, microbridges in Hall bar geome-try were patterned along the two orthogonal [1-10] and [001] crys-tallographic in-plane directions by standard UV-photolithographyand argon-ion milling. The dimensions of the Hall bars are 100 ×20 μm2. Patterned samples were post-annealed in flowing O2 for5 h to avoid possible oxygen deficiency and parasitic conductivityinduced by argon-ion milling. Electrical contacts for the transportmeasurement were produced by ultrasonic Al-wire bonding. Resis-tance measurements were carried out in standard four-point probe(FPP) geometry using a Quantum Design physical property mea-surement system (PPMS) equipped with a 14-T superconductingmagnet. Magnetization measurements were performed by means ofa Quantum Design superconducting quantum interference device(SQUID).III. RESULTS AND DISCUSSIONIn Fig. 1, the x-ray reflectivity and θ/2θ x-ray diffraction in thevicinity of the (110) reflection of DSO are presented. From the fit-ting of measured XRR curves the critical angle (αc), film thickness (t)and surface roughness (r) are deduced which reveal a smooth layer-by-layer growth with negligible surface roughness. Symmetric XRDscans of SIO show a single crystalline phase. With decreasing t, thepeak maximum of the (110) film reflection is shifted toward lower 2θvalues, i. e., larger d-spacing due to the in-plane compressive straincaused by the DSO substrate. The out-of-plane lattice spacing (d110)increases from 3.96 Å for t = 50 nm to 4.09 Å for t = 2.3 nm. Laueoscillations on both sides of the (110) reflection evidence a layeredgrowth.Fig. 2 shows the normalized resistivity ρ001(T)/ρ001(300K)and ρ1-10(T)/ρ1-10(300K) of SIO films for the two orthogo-nal in-plane directions for various film thickness t. Generally,ρ001(T) is distinctly smaller compared to ρ1-10(T). In Fig. 2(d),we have plotted the ratio of the normalized resistivity,rn = [ρ1-10(T)/ρ1-10(300 K)]/[ρ001(T)/ρ001(300 K)], as a func-tion of T. The anisotropic behavior can be discussed in termsof the T-dependence of the structural in-plane anisotropy,√(a(T)2 + b(T)2)/c(T), which for bulk SIO24,25 looks very similarFIG. 1. X-ray reflectivity (green symbols) and x-ray diffraction (blue lines) for theSIO films deposited on DSO (110) for different film thickness t. Red solid lines arefits to the reflectivity. Film peak position of the (110) reflection is indicated by arrow.The dashed line indicates the 2θ peak position of the (110) reflection of bulk SIO.to the T-dependence of rn. Interestingly, rn(T) does not change sig-nificantly with decreasing t for t > 2.3 nm. However, for t = 2.3 nm,rn(T) drops down to about 1.08 at 4 K, indicating less anisotropictransport. Possible reason for that is very likely an increase of epi-taxial strain to the SIO layer, which is naturally expected withdecreasing film thickness. Mismatch of thermal expansion betweenSIO and DSO may also lead increasingly to T-dependent structuralchanges, i. e., orthorhombic distortion, with decreasing t, which mayaffect resistivity anisotropy in SIO considerably. The measurementsdemonstrate the impact of the substrate material on the electronictransport and anisotropy of thin (t ≤ 2.3 nm) SIO films.In the following, we will focus on the magnetotransport ofSIO. Magnetoresistance measurements were performed with mag-netic field B perpendicular to the film surface. Figure 3 showsmagnetoresistance MR = R(B)−R(0)R(0) of of patterned SIO micro-bridges for various film thickness t. MR is always positive and dis-plays an anisotropic behavior along the [1-10] and [001] directionwith MR001/MR1-10 > 1. Generally, MR increases with decreas-ing T and increasing B. For the thinnest film (t = 2.3 nm), theanisotropy (MR001/MR1-10) shows a distinct increase. In addition,a field-dependent butterfly-shaped hysteresis occurs for differentfield-sweep direction at T = 2 K. Interestingly, the field-dependenceAIP Advances 9, 125034 (2019); doi: 10.1063/1.5129350 9, 125034-2© Author(s) 2019AIP Advances ARTICLE scitation.org/journal/advFIG. 2. Normalized resistivity ρ(T)/ρ(300 K) as a function of T for the [001] and[1-10] directions and t = 50 nm (a), 9 nm (b), and 2.3 nm (c). The ratio of the nor-malized resistivity, rn = [ρ1-10(T)/ρ1-10(300 K)]/[ρ001(T)/ρ001(300 K)], as a functionof T for different SIO film thickness t = 50, 9, and 2.3 nm (d). The arrow indicatesthe reduction of rn with decreasing t, most prominent for t = 2.3 nm.changes significantly if T is increased to 5 K, see Fig. 3(d). To doc-ument the hysteresis-behavior more clearly, we have plotted againMR at T = 2 K for the low field range -2.5 T < B < 2.5 T in Fig. 4.Magnetic field sweep direction is indicated in the figure byarrows. The hysteresis is obviously more pronounced for the [1-10]direction. The minima around 0.5 T (for upward sweep-direction)and -0.5 T (for downward sweep-direction) are anomalies withpronounced deviations from classical B2-dependence of MR whichare very likely caused by weak antilocalization. Such features, typ-ically occurring at B = 0 for SIO on STO are well known forthin SIO films20 and are caused by the strong SOC of the iri-dates. Interestingly, the hysteretic behavior of MR disappears forT ≥ 5 K which hints to magnetic order in the film below 5 K.Such an anomalous and anisotropic behavior of MR is not observedfor SIO films on STO, which strongly suggests influence of theDSO substrate material. DSO displays strong paramagnetic behav-ior with antiferromagnetic ordering at TN = 3.1 K.26,27 In addi-tion, the Dy-moments display canted alignment, which gives riseto a net magnetic moment and hence hysteretic behavior belowTN.26 In addition, DSO displays strong magnetic anisotropy with[1-10] direction as easy axis and [001] direction being the hardaxis.The simultaneous appearance of hysteretic effects below 5 Kon resistivity and magnetic moment for SIO and DSO, respec-tively, strongly hints to a substrate-induced mechanism as a reasonfor the anisotropic magnetotransport in SIO. The strong magneticanisotropy of DSO likely results in a large spin-polarization of SIOcharge carriers along the [1-10] direction, i. e., the easy axis directionFIG. 3. Magnetoresistance MR at T = 2 K for the [1-10]- (red line) and [001]-direction (blue line) of a patterned SIO film on DSO with t = 50.0 nm (a), t = 9.0 nm(b), and t = 2.3 nm (c). (d) MR for t = 2.3 nm at T = 5 K.of DSO, if magnetic field is applied. Consequently, spin-flip scat-tering becomes less effective along the [1-10] direction which mayexplain the reduced MR compared to that of the [001] direction.Reducing the film thickness makes substrate induced effects moretransparent, and thus, anisotropic MR is stronger in the thinnestfilm. Possibly, substrate induced spin-polarization in SIO is signif-icant in the vicinity of the substrate/film interface and hence limitedto the first few SIO monolayers. More detailed information on thethickness of the spin-polarized layer has to be figured out by furtherexperiments.FIG. 4. Low-field MR for a thin SIO film (t = 2.3 nm) on DSO at T = 2 K for the[1-10] (red color) and the [001] (blue color) direction. The arrows indicate upward(dashed lines) and downward (solid lines) sweep-direction for the [1-10] direction.AIP Advances 9, 125034 (2019); doi: 10.1063/1.5129350 9, 125034-3© Author(s) 2019AIP Advances ARTICLE scitation.org/journal/advIV. SUMMARY AND CONCLUSIONSThe magnetotransport properties of SIO films on DSO sub-strates have been investigated. The measurements demonstrate thatthe MR is always positive and displays weak-antilocalization forT < 10 K and B < 2 T. The MR shows anisotropic behavior forthe [1-10] and [001] direction with MR1-10 < MR001. In addition,a butterfly-shaped hysteresis is observed for the thinnest SIO film(t = 2.3 nm) on DSO below 5 K. The observed anisotropy and hys-teretic behavior of the MR evidence substrate-induced impact on themagnetotransport in thin SIO films.ACKNOWLEDGMENTSWe would like to thank R. Thelen and the KarlsruheNano Micro Facility (KNMF) for providing us the Atomic ForceMicroscopy facility. We also thank J. Schubert from the Peter Grün-berg Institut, Forschungzentrum Jülich, for Rutherford backscat-tering spectrometry measurements. AKJ acknowledges DAAD forfinancial funding within India IIT Master Sandwich Programme(57434206). AKJ and DF also acknowledge S. Mukherjee and K. Senfor fruitful discussions.REFERENCES1W. Witczak-Krempa, G. Chen, Y. B. Kim, and L. Balents, Annu. Rev. Condens.Matter Phys. 5, 57 (2014).2G. Cao and L. DeLong, Frontiers of 4D- and 5D-Transition Metal Oxides (WorldScientific, 2013).3J. P. Clancy, N. Chen, C. Y. Kim, W. F. Chen, K. W. Plumb, B. C. Jeon, T. W. Noh,and Y. J. Kim, Phys. Rev. B - Condens. Matter Mater. Phys. 86, 195131 (2012).4A. Shitade, H. Katsura, J. Kuneš, X. 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Magnetotransport of SrIrO₃ films on (110) DyScO₃

https://publikationen.bibliothek.kit.edu/1000104608/53736543

Magnetotransport of SrIrO₃ films on (110) DyScO₃

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