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Abstract: Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of La 0.9 Ba 0.1 MnO 3 thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn e g orbitals can be switched from the d 3 z 2 − r 2 orbital to the d x 2 − y 2 orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn 3 d -O 2 p hybridization leads to dramatic modulation of the magnetic and electronic properties of strained La 0.9 Ba 0.1 MnO 3 thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the La 0.9 Ba 0.1 MnO 3 system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.

Open Access

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Abstract: Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180∘ and 90∘ domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance.

Open Access

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Abstract: In antiferromagnetic spintronics, the read-out of the staggered magnetization or Néel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Néel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-established read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are only slightly diminished. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Néel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.

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Abstract: Antiferromagnets are of potential use in spintronic devices due to their ultrafast dynamics, insensitivity to external magnetic fields and absence of magnetic stray fields. Researchers have observed large, transient changes in the electrical resistance in some antiferromagnetic thin film devices after applying electrical or optical pulses. Although the origin of these effects was unknown, it is now understood that they are related to the magnetic order. Researchers from the Czech Academy of Sciences and Charles University in Prague, the University of Nottingham, ETH Zurich, the University of Regensburg in Germany and Diamond Light Source investigated the micro-scale antiferromagnetic order in CuMnAs films before and after applying current pulses. They aimed to relate changes in the electrical resistance to changes in the magnetic microstructure. Using the X-PEEM End station on Diamond’s Nanoscience beamline (I06) enabled them to take images of the antiferromagnetic structures in microscale device structures. Electrical contacts on the sample allowed them to probe the magnetic state before and after applying current pulses. The results show that a fragmentation of micrometre-scale antiferromagnetic domains accompanies the changes in the electrical resistance. The resulting textured structure has lengthscales comparable to, or even smaller than, the 30 nm spatial resolution of the X-PEEM End station. Their results establish a clear relationship of the electrical resistance changes with changes in the micromagnetic structure. The electrical switching and relaxation behaviour they observed can potentially mimic the characteristics of neural network components, offering the potential to develop efficient and high-speed neuromorphic computing applications that mimic neuro-biological architectures present in the human nervous system.

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Abstract: Understanding the electrical manipulation of the antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequencies. Focusing on collinear insulating antiferromagnetic Ni O / Pt thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the Néel-vector direction changes. We demonstrate electrical switching between different T domains by current pulses, finding that the Néel-vector orientation in these domains is along [ ± 5 ± 5 19], different compared to the bulk ⟨ 112 ⟩ directions. The final state of the in-plane component of the Néel vector n IP after switching by current pulses j along the [ 1 ± 1 0 ] directions is n IP ∥ j . By comparing the observed Néel-vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as b 0 + 2 b 1 = 3 × 10 7 J / m 3 . This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.