Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T28: Focus Session: Spin-Hall Effect II |
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Sponsoring Units: GMAG DMP FIAP Chair: Benjamin Jungfleisch, Argonne National Laboratory Room: 205 |
Thursday, March 5, 2015 11:15AM - 11:51AM |
T28.00001: Spin Hall Effect in Spin Glass Systems Invited Speaker: Yasuhiro Niimi The spin Hall effect (SHE) and its inverse play important roles in spintronic devices as they enable interconversions between charge and spin currents. The conversion efficiency, i.e. the spin Hall angle, strongly depends on detailed material properties, such as the electronic band structure and the nature of impurities. While most of the work has focused on the mechanism of the SHE and the magnitude of the spin Hall angle, there are only a few examples to utilize the SHE such as the detection of the spin Seebeck effect and magnetization switching. Further applications of the SHE are, however, still lacking. In this talk, we address a new direction of utilizing the SHE to probe spin fluctuations near glass temperatures $T_{g}$ of spin glass systems. For this purpose, we chose CuMnBi ternary alloys [1]. When there is no Bi impurity in CuMn, it shows no SHE in the spin transport but shows a typical cusp structure in the thermo-magnetic curves. Once a small concentration of Bi is added in CuMn, a large SHE has been observed as shown in our previous work on Bi-doped Cu [2]. Most remarkable is that the SHE of Cu$_{98}$Mn$_{1.5}$Bi$_{0.5}$ is suppressed far above $T_{g} = $ 10 K and it becomes 10 times smaller than that of CuBi at 5 K. This result clearly shows that the spin current generated by the SHE is much more sensitive to magnetization measurements. \\[4pt] [1] A. Fert \textit{et al}., J. Magn. Magn. Mater. \textbf{24}, 231 (1981).\\[0pt] [2] Y. Niimi \textit{et al}., Phys. Rev. Lett. \textbf{109}, 156602 (2012). [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T28.00002: Scaling of the Anomalous Hall Effect in the Low Conductivity Regime Frances Hellman, Julie Karel, Catherine Bordel, Simca Bouma, Hyeon-Jun Lee Temperature-dependent resistivity, magnetization, magnetoresistance and Hall effect were measured in amorphous and epitaxial Fe$_{x}$Si$_{1-x}$ (0.43$<$x$<$0.71) thin films. The resistivity increases as x is decreased, and changes in the temperature coefficient of resistivity ($\alpha$) are observed with variation in both structure and composition. All films are ferromagnetic and display an anomalous Hall effect (AHE). AHE of the amorphous films is 10 times larger than crystalline films of the same composition. The epitaxial films display a scaling behavior consistent with the intrinsic AHE mechanism. The AHE in the low conductivity regime (amorphous films) shows a scaling with conductivity similar to that seen in low conductivity GaMnAs films despite much larger disorder and carrier concentration in the amorphous films. Amorphous Fe$_{x}$Si$_{1-x}$ in this range of x however is notably not in the insulating hopping regime but is instead a strongly disordered metal, a regime that lacks theoretical understanding of AHE. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T28.00003: Anomalous Hall effect and persistent current due to spin chirality in a diffusive regime Kazuki Nakazawa, Hiroshi Kohno It is known that a non-coplanar spin configuration having spin chirality gives a Berry phase to electrons through the exchange interaction, leading to anomalous Hall effect (AHE). Tatara and Kawamura showed that AHE can result without the concept of Berry phase by treating the exchange coupling perturbatively in a model with discretely distributed spins [1]. Recently, we reexamined the AHE in the same model by considering vertex corrections due to normal impurities [2]. This amounts to electron's diffusive motion and spin conservation at the scattering from normal impurities, and leads to the expression of AH conductivity which satisfies spin conservation. We also investigated a persistent current around the spin chirality as a physical origin of the AH response, and we found that the ``typical'' value of the persistent current reproduces the AH conductivity in the diffusive regime. \\[4pt] [1] J. Phys. Soc. Jpn. {\textbf 71}, 2613 (2002) \\[0pt] [2] J. Phys. Soc. Jpn. {\textbf 83}, 073707 (2014) [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T28.00004: Planar Hall effect (PHE), anisotropy magnetoresistance (AMR), and anomalous Hall effect (AHE) in perpendicularly magnetized synthetic ferromagnets See-Hun Yang, Priscila Barba, Aurelien Manchon, Stuart Parkin Chiral spin torque driven domain wall motion (CIDWM) faster than 300 m/s along the current direction has been reported in perpendicularly magnetized atomically thin Co/Ni bilayers deposited on Pt underlayers [1], making these materials promising for DW-based memory and logic devices. Moreover, most recently even more efficiently domain motion ($\sim$ 750 m/s) by current has been observed from synthetic antiferromagnetic(SAF) racetracks with almost compensated magnetization [2]. In this talk we will present Hall measurement results from SAF Hall bars that exhibit characteristic planar Hall effect and anomalous Hall effect. We discuss the origin of these behaviors. \\[4pt] [1] Kwang-su Ryu, Luc Thomas, See-Hun Yang, S.S.P. Parkin, Nature Nanotechnology 8, 527 (2013).\\[0pt] [2] See-Hun Yang, Kwang-su Ryu,, S.S.P. Parkin, accepted in Nature Nanotechnology. [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 1:03PM |
T28.00005: Phase-Sensitive Detection Of The AC Inverse Spin Hall Effect Invited Speaker: Mathias Weiler Spin pumping [1] is a significant source of damping in ultrathin ferromagnet/normal metal bilayers. In these structures, the magnetization relaxation is enhanced via the diffusion of spin currents across the bilayer interface. The pumped spin currents have both a small dc and dominant ac contributions. The nonlinear dc spin current contribution that arises in ferromagnetic resonance (FMR) has been extensively studied in electrical dc measurements that are enabled by means of the inverse spin Hall effect (iSHE) in the normal metal [2]. The ac charge voltage generated in FMR due to the ac iSHE should be linear in the magnetization precession and thus much larger than the corresponding dc voltage for small precession cone angles [3]. However, any measurement of the ac iSHE voltage needs to take the linear inductive voltages due to Faraday's law into account, as magnetization dynamics in ferromagnet/normal metal bilayers result in both, inductive and possible ac iSHE voltages. These voltage signals are always superimposed and cannot be separated in a measurement scheme that is only sensitive to the magnitude of the signal [4-7]. Moreover, inductive and ac iSHE voltages are estimated to be of the same order of magnitude for typical nm-thick ferromagnetic layers in contact with Pt and share identical symmetry with respect to magnetization orientation. The only qualitative difference between inductive and ac iSHE voltages is their expected phase difference of $\pi$/2. We thus use a phase-sensitive, quantitative technique to separate inductive and ac iSHE signals in a variety of Ni$_{81}$Fe$_{19}$/normal metal thin film bilayers at room temperature. All samples show the expected behavior in terms of damping and dc iSHE voltages from which we find a dc spin Hall angle $\Theta_{\mathrm{SH}}$=0.1 for Pt [8]. Our ac iSHE experiments [9] are carried out using Ni$_{81}$Fe$_{19}$/normal metal bilayers deposited simultaneously with the dc structures. Using Ta, W, Pd, Cu or Nb as the normal metal, we find that the inductive contribution dominates over any ac iSHE signal, in agreement with simple estimates based on the extracted dc spin Hall angles for these materials. However, for Pt, we find a surprisingly large ac iSHE contribution that has a significantly different phase than expected. Similar results are also found in Ni$_{81}$Fe$_{19}$/Cu/Pt trilayers, excluding the possibility of an interfacial origin of the large ac iSHE signal. Modeling of our experimental results in the context of the ac iSHE requires a complex-valued spin Hall angle $\Theta_{\mathrm{SH}}$ of Pt with $\Theta_{\mathrm{SH}}\approx 1$ and $\arg\left(\Theta_{\mathrm{SH}}\right)\approx 110^\circ$ in the investigated frequency range of 7 to 20 GHz. \newline [1] Phys. Rev. Lett. \textbf{88}, 117601 (2002), [2] Appl. Phys. Lett. \textbf{88}, 182509 (2006), [3] Phys. Rev. Lett. \textbf{110}, 217602 (2013), [4] Phys. Rev. Lett. \textbf{111}, 217204 (2013), [5] ArXiv 1401.6407 (2014), [6] Phys Rev. Lett. \textbf{112}, 179901 (2014), [7] Nature Comm. \textbf{5}, 3768 (2014), [8] IEEE Mag. Lett. \textbf{5}, 3700104 (2014), [9] Phys. Rev. Lett. \textbf{113}, 157204 (2014) [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T28.00006: Skew-scattering contribution to anomalous and spin Hall effects in dilute ferromagnetic alloys Bernd Zimmermann The spin Hall effect (SHE) possesses great potential for the generation of pure spin currents, but it is difficult to measure directly. The closely related anomalous Hall effect (AHE) is much easier to access in experiment via a finite Hall voltage. Phenomenologically, the only difference between the two effects is the ferromagnetic order needed for the AHE. \\ In this work [1], we investigate the skew-scattering contribution to the AHE in dilute ferromagnetic alloys from first principles. We compare three state-of-the-art methods and analyze chemical trends by considering 3$d$ impurities in bcc-Fe, as well as magnetic 3$d$ impurities in fcc Pd, Pt and Au. We arrive at general rules to obtain a large anomalous Hall angle, which represents an efficiency for the conversion of a longitudinal into a transverse current. Moreover, we reveal a clear correlation between the AHE and SHE in the alloy s which are based on a nonmagnetic host material. \\[4mm] [1] B. Zimmermann, K. Chadova, D. K\"odderitzsch, S. Bl\"ugel, H. Ebert, D.V. Fedorov, N.H. Long, P. Mavropoulos, I. Mertig, Y. Mokrousov and M. Gradhand, accepted by Phys. Rev. B (2014); preprint on arXiv:1406.2712. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T28.00007: Epitaxial IrMn3 on MgO(111) by sputter deposition Alejandro Jara, Igor Barsukov, Yu-Jin Chen, Brian Youngblood, John Read, Patrick Braganca, Ilya Krivorotov Antiferromagnets are promising systems for spintronic applications due to the absence of stray fields and high spin wave group velocity. Coupling between the charge and spin degrees of freedom in metallic antiferromagnets is a topic of high interest. The chemically ordered compensated antiferromagnet IrMn3 has recently been predicted to show anomalous Hall effect (AHE) arising from its noncollinear spin configuration. The AHE would provide a unique opportunity to probe the order parameter of an antiferromagnet via direct electrical measurements, which should be of tremendous utility for antiferromagnetic spintronics. To quantify and further exploit AHE, IrMn3 must be grown in the L12 phase, which supports ordering of the Mn spins on stacked sheets of Kagome spin lattices. Here we present an experimental study of IrMn3 thin films grown on MgO(111) by sputter deposition. We carry out XRD measurements and identify two quasi-epitaxial phases rotated by 60 deg to each other in the film plane. The IrMn3 is strongly (111)-textured with the $<111>$ axis deviating by less than 2 degrees from the film normal due to oblique deposition of the material. The grain size in our films is determined to be 15 nm, while the dimensionless chemical order parameter of the L12 phase is found to be 0.4. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T28.00008: Spin Hall effects in CuAu-I-type metallic antiferromagnets Wei Zhang, Benjamin Jungfleisch, Wanjun Jiang, John Pearson, Axel Hoffmann, Frank Freimuth, Yuriy Mokrousov We investigated the spin Hall effect of CuAu-I-type metallic antiferromagnets by using spin pumping -- inverse spin Hall effect via a coplanar waveguide ferromagnetic resonance broadband technique. By studying the ratio of the two voltage components (anisotropic magnetoresistance and inverse spin Hall effect) with the metal layer thickness, the spin diffusion lengths of the materials are directly extracted, which further allows the determination of the spin Hall angle. We performed such analysis for polycrystalline FeMn, PdMn, IrMn, and PtMn. In particular, PtMn showed large spin Hall effect that is comparable to Pt. First principle calculations of the intrinsic spin Hall effect reproduce these results. We also demonstrate the epitaxial growth of these metallic crystals and its influence to the spin Hall effects due to different crystalline orientation. This work highlights the importance of both spin-orbit coupling and the magnetic ordering to the spin Hall effects of metals. W.~Zhang, \textit{et al.}, Phys. Rev. Lett. \textbf{113}, 196602 (2014) [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T28.00009: Probing the Inverse Spin Hall Effect and Spin-Orbit Coupling in a Broad Range of Transition Metals by Y$_{3}$Fe$_{5}$O$_{12}$-Based Spin Pumping Hailong Wang, Chunhui Du, P. Chris Hammel, Fengyuan Yang Spin-orbit coupling (SOC) is the underlying mechanism for spin Hall physics and it is generally believed that SOC follows $Z^{4}$ (atomic number) dependence and becomes significant only in heavy elements. We report FMR spin pumping from 20-nm Y$_{3}$Fe$_{5}$O$_{12}$ (YIG) films into a series of 3$d$, 4$d$, and 5$d$ transition metals. We observe surprising large mV-level inverse spin Hall effect (ISHE) voltages in Pt, Ta, W, and Cr and robust ISHE signals in other metals. Using the ISHE voltages and damping enhancement, we determine the spin Hall angles and interfacial spin mixing conductances for these metals. Both 3$d$ and 5$d$ metals exhibit systematic behavior of the spin Hall angle, which reveals the critical role of $d$-electrons in SOC. Our result enriches the understanding of ISHE and broadens the scope of materials available for exploring the rich phenomena enabled by SOC as well as presenting a guidepost for testing theoretical models of SOC in transition metals. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T28.00010: Inverse spin Hall effect in Cr metal Danru Qu, Ssu-Yen Huang, Chia-Ling Chien Spin Hall angle, which measures the conversion efficiency between spin current and charge current, is the most important quantity in spin current phenomena. Sizable spin Halls angle have thus far been reported exclusively in non-magnetic materials of heavy elements, such as Pt and Au [1], and recently in ferromagnetic metals, such as Py [2]. In this work, we use the thermal spin injection method to inject a spin current from ferromagnetic insulator YIG into a 3d metal Cr, which is a well-known antiferromagnet (AF) with spin density ordering. We report the observation of inverse spin Hall effect (ISHE) in Cr with a large spin Hall angle, comparable to that of Ta. Through measurements above and below the N\'{e}el temperature of the AF ordering, we show that the origin of the large ISHE in Cr is not due to its spin density wave AF ordering. Moreover, there is no magnetic proximity effect that plagued Pt and Ta. These features show that Cr can be a superior spin current generator/detector in pure spin current phenomena and devices. \\[4pt] [1] D. Qu, S. Y. Huang, B. F. Miao, S. X. Huang, and C. L. Chien, Phys. Rev. B \textbf{89}, 140407(R) (2014). \\[0pt] [2] B. F. Miao, S. Y. Huang, D. Qu and C. L. Chien, Phys. Rev. Lett.~\textbf{111}, 066602 (2013) [Preview Abstract] |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T28.00011: Towards the terahertz frequency measurement of the Inverse Spin Hall Effect Evan V. Jasper, M.T. Warren, T.T. Mai, J. Brangham, H. Wang, J. Gallagher, F. Yang, R. Vald\'es Aguilar The Inverse Spin Hall Effect (ISHE) has become an important tool in the spintronics field as a promising route for generation and detection of spin currents via charge currents. In particular, when the magnetization of a ferromagnet is resonantly excited by a radio-frequency field, angular momentum can be transferred to a non-magnetic metal to produce a pure spin current (spin-pumping), and the ISHE provides a way to measure the generated spin current in the metal and extract essential spin pumping parameters. Very recently, theoretical predictions of spin pumping from an antiferromagnetic (AF) insulator to a normal metal have attracted significant interest. We will report results of experiments where terahertz pulses of electromagnetic radiation resonantly excite the AF resonance on the AF insulator NiO coupled with a thin film of Pt, and attempt to measure the ISHE voltage at terahertz frequencies. [Preview Abstract] |
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