Session JJ03: V: Emergent Properties of Complex Oxides Bulk, Thin Films, and Heterostructures V

Magnetotransport of the Jeff = 1/2 antiferromagnetic Sr2IrO4Cheng Liang Lu, School of Physics, Huazhong University of Sceince and Technology, Wuhan 430072, China

Iridates have been providing a fertile ground for studying emergent phases of matter that arise from delicate interplay of various fundamental interactions with approximate energy scale. Among these highly focused quantum materials, perovskite Sr2IrO4 stands out and has been intensively addressed in the past decade, since it hosts a novel Jeff=1/2 Mott state and quasi-two-dimensional square antiferromagnetic lattice. In this talk, I will discuss some interesting aspects of magneto-transport of the Jeff=1/2 antiferromagnet Sr2IrO4, including the giant anisotropic magnetoresistance (AMR) reaching ~160%, H-driven AMR-reversal behaviour due to bandgap engineering, and their control by various means such as magnetic/electric field, strain, and chemical substitution.   

Effect of superconductivity on the magnetic properties of YBa2Cu3O7−δ/Pr0.5La0.2Ca0.3MnO3 heterostructures

We studied competing magnetic and superconducting interactions in Pr_0.5La_0.2Ca_0.3MnO₃ / YBa₂Cu₃O_7−δ /Pr_0.5La_0.2Ca_0.3MnO₃ (PLCMO/YBCO/PLCMO) heterostructures. A highly sensitive and selective magnetic field-modulated microwave absorption spectroscopy (MFMMS) technique was used to compare the superconducting properties of single YBCO thin films to PLCMO/YBCO/PLCMO heterostructures. The MFMMS showed clear influence of the PLCMO magnetic state on the superconducting transition and vortex dynamics of the YBCO film. Surprisingly, magnetization measurements revealed that the magnetic anisotropy of PLCMO is strongly modified by the superconducting state of the YBCO layer. Our results, in combination with micromagnetic simulations, suggest that the superconductivity changes the temperature-dependent ratio of the ferromagnetic-metallic and antiferromagnetic-insulating domains.  This unusual observation of the effect of superconductivity on magnetism in these well-studied quantum materials when in proximity shows that they are still a rich playground for new physics.   

Manipulating chiral spin tranport in a room-temperature multiferroic

A collective excitation of the spin structure in a magnetic insulator can transmit spin-angular momentum with negligible dissipation. Here, we report the experimental observation of chiral-spin transport in multiferroic BiFeO3, where the spin transport is controlled by reversing the ferroelectric polarization and resultant chirality. The ferroelectrically controlled chiral magnons produce an unprecedented ratio of up to 40% rectification at room temperature. Utilizing these controllable chiral magnons in BiFeO3, an all-oxide, energy-scalable logic is demonstrated composed of spin-orbit injection, detection, and magnetoelectric control. This observation opens a new chapter of multiferroic magnons.

    

Rare earth size dependence of Nernst thermopower in ferromagnetic perovskites: R0.6Sr0.4CoO3 (R = La, Pr, and Nd)

When a semiconductor or metal is subjected to a mutually perpendicular temperature gradient and an external magnetic field, an electric voltage is induced in the direction perpendicular to both of them and this phenomenon is known as the Nernst effect. Here, we discuss the Nernst thermopower (S_xy) in the ferromagnetic cobaltite perovskites R_0.6Sr_0.4CoO₃  with rare earth cations (R = La, Pr and Nd) of different ionic radii. In addition to S_xy, longitudinal thermopower (S_xx) and resistivity in zero magnetic fields were also measured. In each of these samples, the Nernst thermopower (S_xy) increases rapidly around the ferromagnetic Curie temperature (T_C), and goes through a maximum value at a certain temperature before decreasing at low temperatures.  The field dependence of S_xy hysteresis resembling magnetization suggests anomalous Nernst contribution. The maximum value of S_xy = 0.27 μV/K for H = 2 kOe is found in the sample possessing the largest ionic radius (R = La) in this series.  The field-dependent Nernst and Hall effect measurements were extended up to 5 T  and down to 25 K for Nd_0.6Sr_0.4CoO₃ which shows ferrimagnetic interaction between Nd and  Co sublattices.  Our work guides future studies to be focused on the La-based cobaltite to realize higher S_xy value through optimizing composition and synthesis methods.

    

Anomalous Ferromagnetism of quasiparticle doped holes in cuprate heterostructures revealed using resonant soft X-ray magnetic scattering

We report strong ferromagnetism of quasiparticle doped holes both within the ab-plane and along the c-axis of Cu-O planes in low-dimensional Au/d-La1.8Ba0.2CuO4/LaAlO3(001) heterostructures (d = 4, 8 and 12 unit-cells) using resonant soft X-ray and magnetic scattering together with X-ray magnetic circular dichroism. Interestingly, ferromagnetism is stronger at a hole doped peak and at an upper Hubbard band of O with spin-polarization degree as high as 40%, revealing strong ferromagnetism of Mottness. For in-ab-plane spin-polarizations, the spin of doped holes in O2p–Cu3d–O2p is a triplet state yielding strong ferromagnetism. For out-of-ab-plane spin-polarization, while the spins of doped holes in both O2p–O2p and Cu3d–Cu3d are triplet states, the spin of doped holes in Cu3d–O2p is a singlet state yielding ferrimagnetism. A ferromagnetic-(002) Bragg-peak of the doped holes is observed and

enhanced as a function of d revealing strong ferromagnetism coupling between Cu-O layers along the c-axis.   

First-principles study of magnetoelectric properties enhanced by lattice-domain modifications

One of the most studied ferroelectric components in multiferroic composites is BaTiO₃ (BTO). The (001) surface of the BTO single crystal has two types of lattice domains, namely the a and c domains. Experimental studies show that an applied electric field modulates the distribution of lattice domains in BTO. However, most of theoretical analyses of BTO-based multiferroic composites focused on the magnetic modulation by the electrical polarization in a single domain. Here, we performed first-principles calculations on Co₂FeSi/BaTiO₃(001) heterostructures analysing magneto-electric (ME) constants and the magnetic anisotropy energy (MAE) by considering the spin-orbit coupling explicitly in the Kohn-Sham Hamiltonian. We will demonstrate that larger ME constants are achieved by considering lattice domain modification in BTO, where the MAE analysis reproduces experimental trends.   

Boosting the high bias TMR in ferromagnet/superconductor hybrids with spin-orbit interaction

Spin-resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR), providing room temperature functionality in magnetic tunnel junctions (MTJs). However, it breaks down under applied bias, reducing the TMR above 0.5 V. Here we show a new approach based on spin orbit coupling (SOC) controlled interfacial states in vanadium, providing a strong TMR boost under applied bias in V/MgO/Fe/MgO/Fe/Co structures [1]. The observed increase of TMR is modelled with two nonlinear resistances in series, with the low bias conductance of the first (V/MgO/Fe) being boosted by the SOC-controlled interfacial states, while the second (Fe/MgO/Fe) depends on the alignment of the ferromagnetic layers. At low temperatures, the TMR reduction has been mitigated by using resonant tunneling through quantum well states in thin layers. We have also studied the conductance features of our junctions in the superconducting regime of vanadium (below 4 K), finding periodic features consistent not only with this quantum well states, but also with Andreev reflection processes giving rise to long-range triplet Cooper pairing, which is a promising feature in the emerging field of superconducting spintronics. [1] C. González-Ruano et. al. Adv. Electron. Mater. 2100805 (2021).

    

An Intracellular Antenna For Wireless Probing And Augmentation Of Living Cells

An intracellular antenna can open up unprecedented opportunities for fundamental understanding of biology as well as diagnostics and therapeutics. However, due to fundamental limitations in the miniaturization of conventional antennas developing an antenna that can fit inside a cell and can be possibly extended for use in vivo remains an unmet challenge. Here, we present the Cell Rover, a novel antenna that works on the principle of magnetostriction, can be operated wirelessly from inside a living cell, and can be extended for use in 3D biological systems. It is sub-mm in size and converts incident magnetic energy to acoustic waves, thereby reducing its frequency of operation to the low MHz range which is ideal for living systems. We demonstrate the wireless operation of Cell Rovers in fully opaque, stage VI Xenopus oocytes, for which real-time sensing with conventional technologies is challenging. A gradient magnetic field is used for intracellular injection of Cell Rovers to ensure cell viability following which wireless detection is shown using a gradiometer coil assembly. Cell Rovers with different operating frequencies are also shown to enable multiplexing in cells by uniquely addressing antennas in different cells or tuning to multiple antennas within the same cell. This technology forms the basis for the integration of real-time sensing, modulation as well as power transfer for in-cell nanoelectronic computing and can possibly bring the versatility of information technology inside a living cell.