AVS 67 Session MI-Contributed On Demand: Magnetic Interfaces Contributed On Demand Session

On Demand available October 25-November 30, 2021

Session Abstract Book
(356KB, Oct 26, 2021)
Time Period OnDemand Sessions | Topic MI Sessions | Time Periods | Topics | AVS 67 Schedule

MI-Contributed On Demand-1 Direct Imaging of the Ac Component of the Pumped Spin Polarization With Element Specificity
Santa Pile (Johannes Kepler University Linz, Austria); Taddäus Schaffers (Johannes Kepler University Linz); Sven Stienen (Helmholtz-Zentrum Dresden-Rossendorf); Martin Buchner (Johannes Kepler University Linz); Sebastian Wintz (Max Planck Institute for Intelligent Systems, Germany); Sina Mayr (Paul Scherrer Institute, Switzerland); Johannes Förster (Max Planck Institute for Intelligent Systems); Verena Ney (Johannes Kepler University Linz); Ryszard Narkowicz, Kilian Lenz (Helmholtz-Zentrum Dresden-Rossendorf); Markus Weigand (Helmholtz-Zentrum Berlin); Hendrik Ohldag (Stanford Synchrotron Radiation Laboratory; University of California Santa Cruz); Jürgen Lindner (Helmholtz-Zentrum Dresden-Rossendorf); Andreas Ney (Johannes Kepler University Linz)

For the development of novel spintronic devices, it is important to understand the dynamic magnetic processes on the micro- and nanoscale [1]. In spintronics the generation and manipulation of pure spin currents is in the focus of research activities. Amongst the utilized fundamental effects is spin pumping where a precessing magnetization of a ferromagnet being at ferromagnetic resonance (FMR) transfers angular momentum to an adjacent nonferromagnetic layer [2], i.e. spin current. By using lithographically fabricated micro-resonators it is possible to measure FMR of the small samples with a detection sensitivity of down to 106 spins [3]. These micro-resonators allow combining STXM with XMCD spectroscopy and FMR (STXM-FMR). The STXM-FMR setup enables the visualization of the high frequency magnetization dynamics in the GHz regime with a high lateral resolution of nominally 35 nm and a time resolution of 17.4 ps [4]. In this contribution we present the STXM-FMR results for thin magnetic Py (Ni80Fe20) microstrips with the lateral dimensions: 5x1 µm2 measured individually and adjacently to the Co-doped ZnO thin film.

Two types of samples were investigated: single Py microstrips and a heterostructure consisting of Co-doped ZnO thin film with the Py microstrip placed on top (Co:ZnO/Py) in order to investigate the ac component of the pumped spin polarization directly inside the nonferromagnet with ultimate spatio-temporal resolution and elemental selectivity. For FMR and STXM-FMR measurements a static magnetic field was applied in the plane of the strips. Both FMR and STXM-FMR measurements confirm that quasi-uniform and spin-wave modes can be excited in the Py microstrips. The results for the single Py strip show, that with increasing the static magnetic field it is possible to observe the transition from one mode to another and additionally observe superposition of the modes in-between the FMR signals. When superposition of the modes occurs, a non-standing character of the spin-waves can be observed for the Py strip. For the Co:ZnO/Py sample we demonstrate the feasibility to investigate the lateral distribution of the pumped ac spin polarization inside the adjacent non-ferromagnet, when Py microstrip is driven into quasi-uniform main FMR excitation or a spin-wave excitation [5].

Financial support by the Austrian Science Fund (FWF), Project No. I-3050 is gratefully acknowledged.


[1] H. Stoll et al., Front. in Phys. 3, 26 (2015).

[2] Y. Tserkovnyak et al., Phys. Rev. Lett. 88, 117601 (2002).

[3] R. Narkowicz et al., J. Magn. Reson. 175, 275 (2005).

[4]S. Bonetti et al., Rev. Sci. Instrum. 86, 093703 (2015).

[5] S. Pile et al., arXiv:2005.08728 (2020).
MI-Contributed On Demand-4 Breaking Time-Reversal Symmetry at the M Point: Spin Signal from a Surface State on Tl/Ge(111)
Markus Donath, Philipp Eickholt, Peter Krüger, Sebastian D. Stolwijk, Anke B. Schmidt (Westfälische Wilhelms-Universität Münster, Germany)

We report on an additional effect influencing the observed spin polarization in SARPES (spin- and angle-resolved photoemission) and SRIPE (spin-resolved inverse photoemission) experiments. We detected and analyzed a spin-dependent intensity asymmetry for spin-degenerate surface states at the M point in the unoccupied electronic structure of Tl/Ge(111)-(1x1) [1]. Approximating the initial state by a plane wave, we calculated the SRIPE process and obtained good agreement with the experimental data [2]. Our model reveals that this spin asymmetry at a point of time-reversal invariant momentum (TRIM) is of different origin than other effects discussed in the literature, which are based on the light detection geometry, photon energy, and experimental probing depth of the electrons. Instead, the spin asymmetry in this nonmagnetic material with spin-orbit interaction is caused by breaking the initial-state time-reversal symmetry in the experiment. Since SARPES and SRIPE are based on time-reversed processes, the effect is also expected for SARPES experiments where the outgoing photoelectrons break the time-reversal symmetry in the same way as the incoming electrons in SRIPE experiments. Understanding and considering such experimentally induced spin asymmetries is essential for correctly interpreting spin-resolved (inverse) photoemission data.

[1] P. Eickholt, P. Krüger, S. D. Stolwijk, A. B. Schmidt, and M. Donath, Phys. Rev. B 93, 085412 (2016).

[2] P. Eickholt, P. Krüger, S. D. Stolwijk, A. B. Schmidt, and M. Donath, Phys. Rev. B 101, 165411 (2020).

MI-Contributed On Demand-7 Spin-orbit-induced effects in VLEED experiments from MoS2/Au(111)
Christoph Angrick, Annika Henriksen, Nicole Mutzke, Andre Reimann (University of Münster); Moritz Ewert, Lars Buß (Brandenburg University of Technology Cottbus-Senftenberg); Jens Falta (University of Bremen); Jan Ingo Flege (Brandenburg University of Technology Cottbus-Senftenberg); Markus Donath (University of Münster)

The influence of spin-orbit interaction on low-energy electron reflection from MoS2 on Au(111) was studied by VLEED (very-low-energy electron diffraction) [1,2,3]. Maps of the electron reflectivity and the spin asymmetry of the reflected

electron intensities were measured for a wide range of electron incidence angles and kinetic energies. To account for an adlayer coverage of about 30%, maps of the Au(111) substrate and for a MoS2 bulk sample were measured as well.

The adlayer and substrate signals were distinguished by a comparison of the maps.

For MoS2/Au(111), we obtained a spin asymmetry of the reflected intensities, which shows a characteristic feature with alternating sign in the energy region of a VLEED fine structure [1]. The Au(111) substrate, in contrast, shows qualitatively

different spin-asymmetry features, partially with reversed sign compared with MoS2/Au(111). The results of bulk MoS2 resemble the single-layer data to a great extend. The influence of the substrate on the results will be discussed.

[1] Burgbacher et al., Phys. Rev. B 87, 195411 (2013).

[2] Thiede et al., Phys. Rev. Applied 1 , 054003 (2014).

[3] Angrick et al., J. Phys.: Condens. Matter 33, 115001 (2020).

MI-Contributed On Demand-10 Direct Observation of Spin Accumulation in Cu Induced by Spin Pumping
Junjia Ding (Argonne National Laboratory); Wei Zhang (Oakland University); Benjamin Jungfleisch, John Pearson (Argonne National Laboratory); Hendrik Ohldag (Lawrence Berkeley Lab, University of California, Berkeley); Valentine Novosad (Argonne National Laboratory); Axel Hoffmann (University of Illinois at Urbana Champaign)

Pure spin currents have been ubiquitous in contemporary spintronics research. Despite its pro­found physical and technological significance, the detection of pure spin current has largely remained indirect, which is usually achieved by probing spin-transfer torque effects or spin-to-charge conversions. By using scanning transmission X-ray microscopy, we report the direct detection and spatial mapping of spin accumulation in a nonmagnetic Cu layer without any direct charge current injection. Such a pure spin current is induced by spin pumping from a Ni80Fe20 layer and is not accompanied by concomitant charge motion. The observed frequency dependence indicates that the signal is dominated by a coherent, pure spin current, but the magnitude of the spin accumulation suggests also possible additional thermal contributions. Our technique takes advantage of the X-ray magnetic circular dichroism and the synchronization of microwave with X-ray pulses, which together provide a high sensitivity for probing transient magnetic moment. From the detected X-ray signals, we observe two distinct resonance modes induced by spin pumping, Based on micromagnetic simulations, we attribute these two resonances to non-linear microwave excitations. Our result provides a new pathway for detecting pure spin currents that originate from many spintronics phenomena, such as spin Hall and spin Seebeck effects, and which can be applied to both metal and insulator spin current sources [1].

Work at Argonne, including experimental design and measurement, sample fabrication, data analysis, and manuscript preparation, was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Science and Engineering Division under Contract No. DE-AC02-06CH11357. Use of the Stanford Synchrotron Radiation Light source, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. W.Z. acknowledges the DOE visiting FacultyProgram.


[1] J. Ding et al, “Direct Observation of Spin Accumulation in Cu Induced by Spin Pumping”, Phys. Rev. Research Vol 2, art no. 013262 (2020)


MI-Contributed On Demand-13 Spatially Resolved Ferromagnetic Resonance of a Single Fe3O4 Nanoparticle Chain Using Scanning Transmission X-Ray Microscopy
Thomas Feggeler, Benjamin Zingsem, Ralf Meckenstock (University of Duisburg-Essen, Germany); Hendrik Ohldag (Lawrence Berkeley National Laboratory (LBNL)); Michael Farle, Heiko Wende, Katharina Ollefs (University of Duisburg-Essen, Germany)

Scanning Transmission X-Ray Microscopy imaged Ferromagnetic Resonance (STXM-FMR) [1, 2] at the Fe L3-edge was used for the first-time detection of the magnetization dynamics of a bi-segmented chain of 19 Fe3O4 nanoparticles (particle diameter: 40-50 nm), naturally grown inside a bacterium Magnetospirillum Magnetotacticum MS-1. A uniform resonant excitation within the chain segments was measured element specifically with a spatial resolution of about 50 nm and pico second time resolution. Micromagnetic simulations of a corresponding nano particle chain agree well to the observations made in the experiment. The combination of conventional Ferromagnetic Resonance, micromagnetic simulations and STXM-FMR allows the comprehensive characterization of magnetization dynamics on the nanoscale, necessary for the development of genetically engineered spin wave computing devices, as suggested in [3].


[1] S. Bonetti, R. Kukreja, et al.,Rev. Sci. Instrum. 86, 093703 (2015).

[2] S. Pile, T. Feggeler, et al., Appl. Phys. Lett. 116, 072401 (2020).

[3] B. W. Zingsem, T. Feggeler, et al., Nat. Commun., 10, 1 (2019).

Partial financial support by DFG Project: OL513/1-1 is acknowledged.

Helpful discussions with A. Ney and his team are acknowledged.

MI-Contributed On Demand-16 Scanning NV Magnetometry for Semiconductor Device Analysis
Umberto Celano (IMEC, Belgium); Peter Rickhaus, Hai Zhong (Qnami AG); Florin Ciubotaru (IMEC, Belgium); Laurentiu Stoleriu (Alexandru Ioan Cuza University); Alexander Stark, Felipe Favaro de Oliveira, Mathieu Munsch (Qnami AG); Paola Favia, Maxim Korytov, Patricia Van Marcke (IMEC, Belgium); Patrick Maletinsky (Qnami AG); Christoph Adelmann, Paul van der Heide (IMEC, Belgium)

Scanning NV magnetometry (SNVM) is an emerging quantum sensing technique which allows to measure minute magnetic fields with nanoscale resolution. We present a specific use-case of SNVM: the characterization of magnetic nanowires. Magnetic nanowires are among the essential building-blocks of contemporary spintronic devices since their magnetic properties can be tuned by their geometry, and their fabrication is compatible with standard semiconductor fabrication schemes. While their topography and homogeneity can be well characterized with established techniques, it remains difficult to access their microscopic magnetic properties which are key to improve device performance.

Here, we demonstrate magnetic imaging of ultra-scaled magnetic nanowires by SNVM. The imaging reveals the presence of weak magnetic inhomogeneities inside in-plane magnetized nanowires that are largely undetectable with standard metrology. In this context, we will discuss the potential of SNVM for semiconductor device analysis.

MI-Contributed On Demand-19 Co2Fe1.25Ge0.75: Single-Phase, Highest Magnetic Moment, Highest Curie Temperature
Shambhu KC, Rabin Mahat (The University of Alabama); Sudhir Regmi (University of Alabama); Jia Yan Law (The University of Alabama); Victorino Franco (Universidad de Sevilla); Gary Mankey, William Butler, Arun Gupta, Patrick LeClair (The University of Alabama)

Spintronic device performance is compromised when thermal effects impact magnetic properties and spin polarization of the materials [1]. One way of mitigating this problem is to find materials having a very high saturation moment (MS) and high Curie temperature (TC). The full Heusler alloy Co2FeGe theoretically has promise to meet this demand. However, its inability to form a single-phase compound makes it problematic for application. The addition of a fourth element is sometimes useful in stabilizing a single-phase compound [2], but it can be detrimental to some properties, particularly due to the increased probability of chemical disorder. In this talk, we present the successful synthesis of a single-phase compound based on Co2FeGe, viz Co2Fe1.25Ge0.75, by altering the stoichiometry rather than adding a fourth element. For the single-phase compound, MS as high as 6.7 ± 0.1 μB/f.u. at 5K and a Curie temperature of 1135 ± 5 K are measured – to our knowledge the highest reported for full Heusler alloys. In addition, thin films of Co2Fe1.25Ge0.75 deposited on Al2O3(110) and MgAl2O4(100) substrates are highly epitaxial. The structural quality of the films can be argued to be among the best reported for Heusler films to date. The thin film MS values also agree with the bulk MS. First principle calculations suggest the system exhibits total energy minimum at the experimental lattice parameter. These calculations also predict an enhancement in magnetization with a value closer to the experimental value. Hence, the highest moment, highest Curie temperature, and the ability to grow excellent quality single crystal films make Co2Fe1.25Ge0.75 a strong candidate for many device applications.

1. Wurmehl et al., Phys. Rev. B 72, 184434 (2005).

2. KC et al., Phys. Rev. Materials 3, 114406 (2019).

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MI-Contributed On Demand-22 Defects in Magnetic Weyl Semimetal Co3Sn2S2
Zheng Gai, Qiang Zou, Mingming Fu, Lizhi Zhang (Oak Ridge National Laboratory); Rui Xue (University of Tennessee Knoxville); Jiaqiang Yan (Oak Ridge National Laboratory); Mandrus David (University of Tennessee Knoxville); Mina Yoon (Oak Ridge National Laboratory, USA)

Co3Sn2S2 is a magnetic Weyl semimetal with kagome-lattice. In such samples, the existence of bulk Weyl nodes, which are formed under broken inversion or time-reversal symmetry, creates nontrivial topological properties like robust Giant anomalous hall effect. The surface–bulk correspondence ensures the bulk bands related topological “Fermi arc” surface bands dispersion. In this presentation, we use low temperature high magnetic field scanning tunneling microscope, spin polarized STM, and quasiparticle interference (QPI) to study the influence of local defects to the Weyl nodes movement, including magnetic and nonmagnetic vacancies and adatoms. S, Co and Sn vacancies and adatoms are identified, their behavior under magnetic field are studied. The interplay among topology, defects and magnetism are discussed for the understanding of the involved quantum phenomena.

This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

MI-Contributed On Demand-25 Optimizing Magneto-Elastic Coupling in Multilayer Fega/NiFe Thin Films for Magneto-electric Applications
Adrian Acosta, Jane Chang (UCLA)

Magnetoelectric (ME) materials provide the ability to efficiently control magnetism with electric fields, offering the potential to circumvent the size and efficiency limitations of traditional electronic devices. One barrier towards enhancing the efficiency in ME devices is the need for ferromagnetic materials that exhibit both a large magnetostriction and soft magnetic properties to yield a high magneto-elastic coupling. Additionally, for microwave ME applications, a low Gilbert damping is needed for low loss operation whereas materials with large magnetostriction typically exhibit high Gilbert damping coefficients due to their large spin lattice coupling (α ~ 0.2 vs ~ 0.03 for most ferromagnetic metals).

FeGa is a material of interest due to its large magnetostriction (~275 ppm in polycrystalline bulk) and large piezomagnetic coefficient (>2 ppm/Oe) but is highly lossy at high frequencies and exhibits a large magnetic hysteresis. Recent studies of FeGa/NiFe (1:1 volume fraction) multilayer (ML) thin films [1-2] have found that these nanolaminates can achieve a low coercivity (<10 Oe) and can reach a >4x increase in magnetoelectric coefficient compared to single phase FeGa films. However, prior work on FeCo/NiFe suggests that only a thin interlayer of NiFe is required to achieve a significant enhancement in soft magnetic properties [3]. In this work, we explore a multilayering strategy of FeGa with NiFe – (100 nm FeGa / N)/ (2.5 nm NiFe) – where N represents the total number of bilayers. It was found that 2 bilayers optimized the lowest in-plane coercivity (7 Oe) and Gilbert damping coefficient (0.014). Compared to multilayers with an insulating layer insertion, this is less than an order of magnitude lower than reported FeGaB(25 nm)/Al2O3/FeGaB(25 nm) (α = 0.24) [4] and within the same order of magnitude for MLs we have previously studied of FeGa(10 nm)/NiFe(10 nm)/FeGa(10nm) with an Al2O3 insertion (α = 0.006).

Furthermore, it is expected that the magnetostriction increases linearly with the number of bilayers as the contribution from interfacial magnetostriction also increases. XRD and AFM imaging are used to correlate the coercivity, gilbert damping, and magnetostriction with the grain size and surface roughness of the composite film with increasing number of bilayers. This ML strategy shown here can be used to help design materials with a higher magneto-elastic coefficient for strain-mediated magnetoelectric devices.


1. Rementer, Colin R., et al. Appl. Phys. Lett. 110.24 (2017): 242403

2. Shi, Jiaxing, et al. J. Alloys Compd. 806 (2019): 1465-1468

3. Rengarajan, S., et al. J. Appl. Phys. 81.8 (1997): 4761-4763

4. Imran, Shahid, et al. Rare Metal Mat. Eng. 47.7 (2018): 1951-1957

MI-Contributed On Demand-28 Large Temperature Dependent Spin Torque Efficiency in Antiferromagnetic FeRh
Jonathan Gibbons (University of Illinois at Urbana Champaign); Takaaki Dohi (Tohoku University, Japan); Hilal Saglam (Yale University); John Pearson (Materials Science Division, Argonne National Laboratory); Shunsuke Fukami (Tohoku University, Japan); Axel Hoffmann (University of Illinois at Urbana Champaign)
Magnetic ordering is an attractive trait in spin source materials for spintronics applications, as this ordering can break the material's symmetry and allow for ordinarily forbidden exotic spin torques ideal for efficiently controlling perpendicularly magnetized nanomagnets or driving spin torque oscillators for energy-efficient neuromorphic computing. In ferromagnetic materials, controlling the magnetic ordering direction can control the spin polarization of the generated spin currents. Iron rhodium (FeRh) exhibits a transition between a low-temperature antiferromagnetic (AFM) state and a high-temperature ferromagnetic (FM) state. For appropriate growth parameters, this transition can be found close to 300K, such that both the FM and AFM states are stable at room temperature, making it an ideal material for probing the influence of magnetic ordering on spin geometry. We investigate the influence of magnetic ordering and present measurements of the spin torque efficiency in iron rhodium over a range of temperatures, and report large exotic spin torques in anti-ferromagnetic FeRh that grow significantly as the temperature is varied, and consider the possible influence of magnetic ordering on these findings.
This work was supported as part of Quantum Materials for Energy Efficient Neuromorphic Computing, an Energy Frontier Research Center funded by the U.S. DOE, Office of Science.
MI-Contributed On Demand-31 Effect of Sn Doping on Surface States of Bi2Se3 Thin Films
Jennifer DeMell, Gregory Stephen (Laboratory for Physical Sciences); Ivan Naumov (Howard University); Siddharth Tyagi (University of Maryland, College Park); Owen Vail (Army Research Laboratory); Michael Dreyer (University of Maryland, College Park); Robert Butera, Aubrey Hanbicki (Laboratory for Physical Sciences); Patrick Taylor (Army Research Laboratory); Isaak Mayergoyz (University of Maryland, College Park); Pratibha Dev (Howard University); Adam Friedman (Laboratory for Physical Sciences)
Bi2Se3, widely studied as a topological insulator, has great potential for applications in low-power electronics and quantum computing. Intrinsic doping, however, presents a persistent challenge, leading to predominantly bulk conduction. In this work, we use substitutional Sn dopants to control the Fermi level in Bi2Se3 films. Scanning tunneling microscopy (STM) shows a shift in the local density of states toward the Dirac point as more Sn is incorporated. Density functional theory calculations elucidate the STM results, showing that Sn adds metallic states near the Fermi level that are localized to the defect sites while leaving the Dirac cone undisturbed. Electronic transport measurements demonstrate that the Sn defects increase the separation between bulk and surface states, though bulk conduction remains a dominant component.
MI-Contributed On Demand-34 Control of Domain Wall Patterning and Anomalous Response Functions in Ferrimagnetic Spinels
Lazar Kish (University of Illinois at Urbana-Champaign); Alex Thaler (Oak Ridge National Laboratory); Minseong Lee (Los Alamos National Laboratory); Alexander Zakrzewski (University of Illinois at Urbana-Champaign); Dalmau Reig-i-Plessis (University of British Columbia); Brian Wolin, Xu Wang (University of Illinois at Urbana-Champaign); Ken Littrell (Oak Ridge Natinal Laboratory); Raffi Budakian (University of Waterloo); Haidong Zhou (University of Tennessee Knoxville); Zheng Gai, Matthias Frontzek (Oak Ridge National Laboratory); Vivien Zapf (Los Alamos National Laboratory); Adam Aczel, Lisa DeBeer-Schmitt (Oak Ridge National Laboratory); Gregory MacDougall (University of Illinois at Urbana-Champaign)

The ferrimagnetic spinels are known for anomalous magnetoresponsive behaviors which stem from strong spin-lattice coupling and orbital ordering effects. Single crystals of these materials (Mn3O4, MnV2O4, FeV2O4) display a nanometer length-scale patterning of magnetostructural domains which is strongly correlated with these effects. The domain patterns are remarkably sensitive to environmental stress and controllable by applied magnetic fields. In this talk, we present reciprocal-space characterizations of these mesoscale patterns using small-angle neutron scattering, which allows us to correlate various response functions including inverse magnetoelastic effect and magnetodielectric effects with the onset and field response of domains. Meanwhile, neutron diffraction and small-angle X-ray scattering reveal a strong intertwining of these effects with lattice degrees of freedom, collectively establishing strain as an important tuning parameter for anomalous behavior in these materials.

MI-Contributed On Demand-37 Anomalous Hall Effect in Heterostructures Based on MnBi2Te4 Grown by MBE
Seul-Ki Bac, Logan Riney, Jiashu Wang (University of Notre Dame); Kerrie Koller (Saint Mary's College); Xinyu Liu, Maksym Zhukovskyi, Tatyana Orlova, Malgozata Dobrowolska, Jacek Furdyna, Badih Assaf (University of Notre Dame)

The intrinsic magnetic topological insulator MnBi2Te4 provides a great platform to explore quantum phenomena, such as quantum anomalous Hall effect and axion insulators, as reported earlier. However, the search of interesting electromagnetic effects in this material was hindered by the difficulty of preparing its high-quality films with well-controlled composition and thickness. In this study, we compare three different types of Mn-Bi-Te samples grown by molecular beam epitaxy: a heterostructure of MnBi2Te4 and Bi2Te3, a single MnBi2Te4 layer, and a heterostructure of MnBi2Te4, Bi2Te3, and MnTe. We measured the anomalous Hall effect (AHE) in each case and demonstrate its evolution from a two-component AHE contain the contribution of the MnTe and MnBi2Te4, to single component AHE resulting from few-layer MnBi2Te4 scattered out in a Bi2Te3 matrix, and finally to an antiferromagnetic AHE, characteristic of the pure phase of MnBi2Te4. Our work provides an understanding of the AHE for all three possible heterostructure compositions and paves the way for the realization of new quantum phenomena in pure MnBi2Te4 thin films.

MI-Contributed On Demand-40 Magnetic Transition Behavior of Epitaxial Fe47Rh47Pd6 Films
Gary Mankey (University of Alabama); Hideo Sato (Tohoku University); Neha Pachauri (Intel); Sahar Keshavarz (University of Alabama); Hwachol Lee (Trinity College Dublin); Patrick LeClair (University of Alabama); Oleg Mryasov (Department of Physics and Astronomy)
The structural and magnetic properties of Fe-Rh-Pd epitaxial thin films grown on MgO(001) were studied as a function of growth temperature. Films grown above 400 C exhibit a first-order antiferromagnetic to ferromagnetic magnetic phase transition with a transition temperature that decreases as the growth temperature is increased. The chemical order parameter of the Fe-Rh-Pd films is nearly independent of the growth temperature, while the lattice constants change slightly. A comparison of our structural, magnetic, and electrical transport results with first-principles-based calculations as well as literature results indicate that the transition temperature of Fe-Rh-based alloy films depends sensitively on the lattice parameters, and is of electronic origin. The transition temperature and its width can be tuned over a wide range by controlling the crystal structure via growth conditions or post-deposition annealing.
MI-Contributed On Demand-43 The Critical Role of Checkerboard Spin Fluctuations in High-Tc Single Layer Iron Chalcogenide Superconductors
Qiang Zou, Huimin Zhang (West Virginia University); Tatsuya Shishidou, Michael Weinert (University of Wisconsin Milwaukee); Lian Li (West Virginia University)

Single layer FeX (X=Te, Se, S) epitaxially grown on SrTiO3 (STO) substrate represents a model system for probing a host of quantum phenomena due to the interplay of topology, magnetism and superconductivity.

For example, single layer FeTe exhibits long-range bi-collinear antiferromagnetic (AFM) order, which is not superconducting. We found that the AFM order, however, can be suppressed by alloying with Se at >10% concentrations, where enhanced superconductivity emerges [1]. Our spin spiral calculations further showed that the ground state is magnetically disordered paramagnetic, where local checkerboard (CB) AFM fluctuations is critical to the high Tc superconductivity in FeSe [2].

In this work, the impact of S incorporation into single layer FeSe is investigated. Our calculations indicate that the energy difference between CB and co-linear (CL) AFM order increases with increasing S. Fits of the spin-spiral dispersion to spin models leads to Heisenberg parameters J2/J1 of 0.55 for FeSe and 0.72 for FeS, placing the FeS system closer to the CL phase boundary and possibly decreasing the importance of CB fluctuations [3]. Experimentally, we synthesize high quality single layer FeSe1-xSx films on STO(001) substrates by molecular beam epitaxy, and probe their electronic properties using scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy [3]. We observe that with increasing S concentration x, the Fermi surface at M point becomes more anisotropic and the effective mass decreases from 4.3 to 1.2 me, while the hole pocket at Γ point stays at 60 meV below the Fermi level. More importantly, no Tc enhancement is observed for films with x > 0.7. Our findings demonstrate that the CB AFM fluctuations plays an essential role in the enhanced superconductivity in epitaxial single layeriron chalcogenidesuperconductors on STO.

  1. Zhuozhi Ge, Qiang Zou, Huimin Zhang, Chenhui Yan, Daniel Agterberg, Michael Weinert, and Lian Li. "Superconductivity on Edge: Evidence of a One-Dimensional Superconducting Channel at the Edges of Single-Layer FeTeSe Antiferromagnetic Nanoribbons." ACS Nano14, 6539 (2020)
  2. T. Shishidou, D. F. Agterberg, and M. Weinert. "Magnetic fluctuations in single-layer FeSe." Commun Phys1, 8 (2018)
  3. Qiang Zou, Huimin Zhang, Tatsuya Shishidou, Michael Weinert, and Lian Li. "The critical role of checkerboard spin fluctuations in high-Tc single layer FeSe1-xSx superconductors. " (to be published)

This research is supported by DOE (DE-SC0017632).

MI-Contributed On Demand-46 Magnetic Anisotropy in a Single Crystal Antiferromagnetic Thin Film
Saima Siddiqui (University of Illinois at Urbana Champaign); John Pearson (Argonne National Laboratory); Axel Hoffmann (University of Illinois at Urbana-Champaign)

Antiferromagnetic materials promise to show magnetization dynamics, including switching, at ultra-high frequency and thus are of immense interest for next generation memory and logic applications. Besides, spin waves in an antiferromagnetic insulators propagate very efficiently. However, electrically reading the states of the antiferromagnetic materials is not easy. Recently, spin Hall magnetoresistance (SMR) has been identified as one of the promising ways to access the surface states of the antiferromagnetic insulators. In this work, we focus on α-Fe2O3 insulator. We grow a 200-nm thick α-Fe2O3 film on (11-20) Al2O3 by reactive sputtering at 5 mTorr. A 6­nm thick Pt film is deposited in-situ on the Fe2O3 film. We measure the SMR of the patterned Hall bar structure of Pt at low temperatures and room temperatures. Below the Morin transition, we observe positive and negative magnetoresistance in the Pt/Fe2O3 bilayers depending on the direction of the current flow at the spin flop transition. This identifies that SMR can clearly determine the anisotropy of a thin film antiferromagnetic insulator. Moreover, we observe the spin-flop field of α-Fe2O3 using the Hall measurement in addition to the SMR measurement. The Hall magnetoresistance is 100x higher than the SMR at the spin-flop field. We will show a detailed study of the dependence of magnetoresistance on angular fields at different temperatures. Our study reveals important physical phenomena in the antiferromagnetic Fe2O3 thin film, which in turn will help to design energy efficient antiferromagnetic devices.

This work was supported by the Illinois MRSEC funded by NSF and by the US DOE BES Materials Science and Engineering Division.

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Time Period OnDemand Sessions | Topic MI Sessions | Time Periods | Topics | AVS 67 Schedule