Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R39: Novel Magnetic Characterization TechniquesFocus
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Sponsoring Units: GMAG DMP Chair: Lisa DeBeer-Schmitt, Oak Ridge National Laboratory Room: BCEC 207 |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R39.00001: Investigation of Diverse Magnetic Materials via Acoustically Driven Ferromagnetic Resonance Piyush Shah, Derek Bas, Vladimir Safonov, Maksym Popov, Alexei Matyushov, Anne Kittmann, Viktor Schell, Eckhard Quandt, Nian Xiang Sun, Gopalan Srinivasan, Brandon Howe, Michael E McConney, Michael Page Magnetoelastic coupling has been exploited to detect FMR using surface acoustic waves(SAWs), a technique known as ADFMR. GHz-frequency SAWs are produced and detected electrically using pairs of interdigital transducers(IDTs). A magnetic film is placed in the path of the SAWs, which can then interact with magnetic moments via magnetoelastic coupling. Absorption of the SAWs occurs at FMR, modulating the measured output. Landau-Lifshitz-Gilbert theory describes the interaction in terms of the external magnetic field with a characteristic four-lobe pattern, from which the magnetic anisotropy field, FMR resonance field, and magnetoelastic coupling coefficient can be inferred. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R39.00002: Enhanced-Spectral-Range Brillouin Light Spectroscopy by sub-diffraction confinement of light Ryan Freeman, Robert Lemasters, Feng Wang, Vladislav Demidov, Sergej Demokritov, Hayk Harutyunyan, Sergei Urazhdin Microfocus Brillouin Light Spectroscopy (BLS) is a standard optical technique which allows for the direct observation of quasiparticles such as phonons or magnons in magnetic films. A major limitation of the technique is that due to the small wavevector of light, the technique is only sensitive to the dynamical modes near the center of the Brillouin zone, making a large part of the spectrum optically inaccessible. We show that by using a nanoscale optical mask on top of the magnetic film, the BLS signal from short-wavelength spin waves can be enhanced by up to an order of magnitude. The enhancement is consistent with the broadened distribution of wavevectors caused by the spatial confinement of light, analogous to the uncertainty principle. Additionally, by engineering the geometry of the optical mask, we selectively enhance the sensitivity to specific spin wave modes, allowing us to reconstruct the spin wave dispersion. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R39.00003: Coupling of Nitrogen Vacancy Centers to Pinned Domain Walls in Magnetic Nanowires Jeffrey Rable, Eric Kamp, Benjamin S Piazza, Nitin Samarth Nanodiamonds containing nitrogen vacancy (NV) centers have emerged as a robust system for measuring magnetic structures on the nanoscale. In addition to their use in studying static magnetic structures, such as stationary domain walls[1], they have recently been used to probe dynamic phenomena, such as ferromagnetic resonance[2] and spin wave propagation[3]. Here, we investigate the coupling of NV centers to pinned domain wall oscillations in a notched ferromagnetic nanowire made of permalloy. To design a nanowire that oscillates at NV resonance frequencies, we used micromagnetic simulations to test various wire sizes and notch geometries. Next, we used a pick-and-place method to position the nanodiamonds at the domain wall pinning site using an atomic force microscope. We then performed measurements using microwaves and a homebuilt confocal microscope. These methods pave the way for future measurements of domain wall dynamics with NV centers and more advanced methods of NV qubit control. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R39.00004: NV Diamond Based Broadband Readout of FMR from Organic Magnetic V[TCNE]2 Thin Film Brendan McCullian, Michael Chilcote, Vidya P Bhallamudi, Carola Purser, Ezekiel Johnston-Halperin, P Chris Hammel Low damping magnetic thin films will play a key role in realizing nanoscale spin based computational elements. Organic-based magnetic films have shown high-quality resonance properties which rival the best oxides, and can be deposited across a wide range of substrates. A local probe of magnetic resonance is desirable for nanoscale characterization since inductive based techniques typically require large samples and can be spatially insensitive. The Nitrogen-Vacancy (NV) defect in diamond can serve as a platform for local, broadband, optical readout of magnetic resonance from a proximal magnetic film. We report broadband optically detected ferromagnetic resonance (ODFMR) from a micron-thick layer of the high quality organic-based ferrimagnet Vanadium Tetracyanoethylene (V[TCNE]2) grown on a diamond substrate. The locally probed FMR exhibits linewidths on the order of 1 Gauss, indicating both the high quality of the VTCNE on the micron scale and of the ability of the NV as a sensor for low damping materials. This work demonstrates the utility of the NV center to measure FMR of low Ms and organic systems. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R39.00005: THz Spectrum Analysis Using an Antiferromagnetic Tunnel Junction as a Signal Mixer Steven Louis, Petro Artemchuk, Olga Sulymenko, Vasyl S Tyberkevych, Jia Li, Oleksandr Prokopenko, Andrei Slavin We propose a novel, all-electrical method of performing spectrum analysis between 0.1 THz to 1.0 THz (in the “THz gap”). The method features an antiferromagnetic (AFM) tunnel junction that consists of 4 thin layers (Pt, AFM, MgO, Pt) and functions as follows [1]. First, an in-plane dc bias current I(t) in the Pt layer creates perpendicular spin Hall current, which excites rotation of the AFM sublattices with a frequency f(t) ~ I(t). When the bias current I(t) increases with time, f(t) can be linearly swept over the THz gap. Due to the tunneling magnetoresistance effect, the resistance R(t) of the MgO/Pt structure oscillates with the same frequency f(t). Oscillating resistance R(t) is mixed with an input signal producing low-frequency output voltage V(t) that temporally encodes the input spectrum. The spectrum can be extracted from V(t) using signal processing method described in [2]. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R39.00006: Incoherent ferromagnetic spinwave spectroscopy using defect spins in diamond Carola Purser, Vidya P Bhallamudi, Denis Pelekhov, Qiaochu Guo, Gregory Fuchs, P Chris Hammel Optically detected spin transitions in nitrogen vacancy (NV) centers in diamond sensitively detect fluctuating fields at NV transition frequencies. Applied to ferromagnetic dynamics, this has enabled sensing of thermally occupied spinwaves as well as broadband, off-resonant spectroscopy of driven uniform-mode ferromagnetic resonance. We measure the relaxation rates of NV sensor spins to detect thermally excited spinwaves from a thin film of permalloy (Py). Analytical calculations and micromagnetic simulations demonstrate good agreement with measured NV relaxation rate as a function of NV-Py separation and applied field strength. Notably, NV sensors detect field noise from Py at a separation of up to 450 nm, thus demonstrating the suitability of NV probes in the GHz frequency range and submicron length scales of interest for communication and information devices. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R39.00007: A single electron spin to study magnons in a magnetic insulator Tony X. Zhou, Joris Carmiggelt, Lisa Gachter, Amir Yacoby A single electron spin as a quantum sensor is an ideal tool to study novel condensed matter physics. Recently, NV center in diamond has been used as a single electron spin sensor to explore topics of skyrmion[1] and spin chemical potential in ferromagnetic insulator[2]. In this work, we use a single NV center in scanning probe microscope[3] to study magnons in yttrium iron garnet (YIG). |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R39.00008: Crossover of tip-sample magnetic couplings in an in-field spin-polarized scanning tunneling microscopy Soohyon Phark, Dirk Sander We report a crossover between long- and short-range magnetic couplings in an atomic scale magnetic tunnel junction (MTJ), measured from a tip-sample distance dTS-resolved spin-polarized scanning tunneling microscopy of a Co nanoisland with Fe tips. We show that superparamagnetic response of tip magnetization [1] quantitatively measures the sample-induced field at the tip position μ0HS(dTS), which results in non-zero field offset Hoff in the field-dependent differential conductance hysteresis. The Hoff(dTS) with a varying dTS quantitatively characterizes a dipole filed of ~60 mT. On the other hand, a short range coupling, which is characterized as an antiferromagnetic tip-sample coupling, is observed at a small dTS. This strongly increases for a decreasing dTS and competes with the dipole field, resultantly, leading to a crossover of the magnetic couplings from parallel to antiparallel. Our works demonstrate a novel method for quantitative measurement of magnetic couplings in an atomic scale MTJ under a simple and precise control of its tunnel barrier thickness. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R39.00009: Spin polarized scanning tunneling microscopy with EuS coated W tip Hoyeon Jeon, Minjun Lee, Young Kuk Various kinds of ferromagnetic or antiferromagnetic tips have been used to measure local magnetic properties of surfaces in spin polarized scanning tunneling microscopy technique. In this study, europium sulfide (EuS) coated tungsten tip is used because EuS coated tip is known to have a Sherman factor of 0.85 due to its exchange splitting [1,2]. With this tip, we have imaged different magnetic domains on iron islands grown on W(110) surface. The differential conductance was mapped at liquid helium temperature because Curie temperature of EuS is 16K. We were able to manipulate the magnetization orientation of a ferromagnetic domain of Fe island by spin polarized tunneling current. We measured magnetic properties of single-layer FeSe film on SrTiO3 to confirm a theory that predicted antiferromagnetic order on Fe layer in the film. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R39.00010: Determination of 167Er:YSO Spin Hyperfine and Quadrupole Tensors using Josephson Bifurcation Amplifier Rangga Budoyo, Kosuke Kakuyanagi, Hiraku Toida, Yuichiro Matsuzaki, William John Munro, Shiro Saito Using an ESR spectrometer based on Josephson Bifurcation Amplifier, we performed spectroscopy of Erbium-doped Y2SiO5 crystal at various magnetic field orientations and strengths. By fitting the resulting spectra, we extracted the ground state hyperfine and quadrupole tensor values for 167Er:YSO. We discuss these tensor values, and compare them with values obtained using other methods, including conventional ESR spectroscopy, tunable resonators, and optical methods. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R39.00011: Neutron Depolarization Microscope for Imaging of Ferromagnetic Phase Transitions: Ni3Al and HgCr2Se4 under pressure Boris Khaykovich, Pau Jorba, Michael Schulz, Daniel Hussey, Muhammad Abir, Marc Seifert, Vladimir Tsurkan, Alois Loidl, Christian Pfleiderer We performed spatially resolved neutron depolarization imaging of a large Ni3Al crystal, and a small HgCr2Se4 spinel under pressure, to probe bulk magnetic inhomogeneities in the ferromagnetic phase and the transition temperature with the spatial resolution of 100 μm. To obtain such resolution, we employed a new technique, a neutron microscope based on image-forming Wolter optics and a focusing guide. The depolarization images of Ni3Al show that the sample doesn't homogeneously go through the ferromagnetic transition; the improved resolution allows us to identify previously unidentified high-TC regions. The results on HgCr2Se4 highlight the advantage of this technique especially for complex sample environments such as pressure cells. The improved resolution allows to image domain formation in the sample while decreasing the acquisition time. The novel optical design that enabled acquisition of the high spatial resolution neutron depolarization images is described in detail and image results are compared to a conventional radiography setup without a lens. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R39.00012: Imaging Nanoscale Magnetism and its Dynamics at CSX Beamline Wen Hu, Felix Buettner, Claudio Mazzoli, Andi Barbour, Stuart B Wilkins Imaging magnetic materials and structures as a function of external parameters, including magnetic and electric fields, and temperature will provide detailed insight into their dynamics and behavior. Coherent soft x-ray scattering (CSX) beamline at NSLS-II provide researchers a world leading coherent high photon flux with full polarization control. Coherent diffraction imaging, such as resonant soft x-ray ptychography and holography, are under commissioning at CSX and welcome new users. Very recently, we monitored thermal motions of magnetic domain wall with high magnetic contrast and 10nm spatial resolution using holography imaging. Moreover, a new holography chamber has been developed and installed at CSX beamline and it provided holography imaging capability to study magnetic materials as a function of temperature under in-situ condition (current injection and in-vacuum magnetic field). |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R39.00013: Extracting equivalent circuit model of magnetoelectric gyrator using vector network analyzer Cheng Tu, Xianfeng Liang, Cunzheng Dong, Huaihao Chen, Zhaoqiang Chu, Nian Xiang Sun The magnetoelectric (ME) effect is a polarization change induced by an applied magnetic field, or conversely a magnetization change induced by an applied electric field. The giant ME effect found in coil-wrapped magnetostrictive/piezoelectric laminated composites can be utilized to realize gyrators. Until now, there is little reported work regarding how to extract the equivalent circuit model of such ME gyrator from measurement. In this work, we report an effective method to accurately extract the equivalent circuit model from the measured impedance parameters using a vector network analyzer (VNA). The two-port ME gyrator under investigation consists of a plate type piezoelectric/magnetostrictive laminate, in which the piezoelectric layer (PZT) is sandwiched between two magnetostrictive layers (metglass). A 30-turn coil is wrapped around the laminate serving as port 1. The metal electrodes on the surfaces of PZT layer are used as port 2. All the model parameters of the gyrator were extracted from the measured impedance parameters using a VNA. Good agreement between the model and measured results proves that the proposed extraction method is valid and accurate. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R39.00014: Capturing Nucleation at 4D Atomic Resolution Yongsoo Yang, Jihan Zhou, Yao Yang, Dennis S Kim, Andrew Yuan, Xuezeng Tian, Colin Ophus, Fan Sun, Andreas Schmid, Michael Nathanson, Hendrik Heinz, Qi An, Hao Zeng, Peter Ercius, Jianwei Miao Nucleation is a ubiquitous phenomenon in many physical and biological processes. However, it is a challenging process to study nucleation due to the lack of experimental tools to directly measure the 3D atomic structure of nuclei. Here, we further advance atomic electron tomography to study the early stage nucleation of FePt nanoparticle system at 4D atomic resolution [1]. We reveal that early stage nuclei are irregularly shaped, each has a core of a maximum order parameter, and an order parameter gradient points from the core to the boundary of the nucleus. We also capture the 3D atomic structure and dynamics of the same nuclei undergoing growth, fluctuation, dissolution, merging and/or division. We find that nucleation dynamics is regulated by the distribution of the order parameter and its gradient. These experimental results differ from classical nucleation theory (CNT), and we propose an order parameter gradient nucleation model which is thermodynamically more favorable than CNT. We further corroborate this model using molecular dynamics simulations of the liquid-solid phase transition of Pt. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R39.00015: Cryogenic Amplification of Magnetoresistance in Magnetic Tunnel Junctions with the Aid of SiGe-HBT Jason Dark, Hanbin Ying, Grant H Nunn, John Cressler, Dragomir Davidovic Cryogenic amplification has been used for qubit readout, single electron transistor operation, and charge sensing with quantum point contacts; however, this useful tool has been missing from electron transport measurements in the broad field of magnetism. Silicon-Germanium Heterojunction Bipolar Transistors were used for cryogenic preamplification of nanoscale magnetic tunnel junctions at 8 K. The preamplification system increased the signal-to-noise ratio of the tunneling magnetoresistance signal by a factor of 6.62. The current gain provided by the preamplification also allowed for a higher bandwidth measurement limited by the external transimpedance amplifier, rather than cryogenic wiring. The high impedance (≈1 MΩ) of the junctions allow for easy migration to study the magnetodynamics of more interesting samples. |
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