Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G7: Focus Session: Magnetic Thin Films |
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Barry Zink, University of Denver Room: 106 |
Tuesday, March 4, 2014 11:15AM - 11:51AM |
G7.00001: Engineered materials for all-optical helicity-dependent magnetic switching Invited Speaker: Eric Fullerton The possibilities of manipulating magnetization without applied magnetic fields have attracted growing attention over the last fifteen years. The low-power manipulation of magnetization, preferably at ultra-short time scales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. Here we explore the optical manipulation of the magnetization of engineered materials and devices using 100 fs optical pulses. We demonstrate that all optical -- helicity dependent switching (AO-HDS) can be observed not only in selected rare-earth transition-metal (RE-TM) alloy films but also in a much broader variety of materials, including alloys, multilayers, heterostructures and RE-free Co-Ir-based synthetic ferrimagnets. The discovery of AO-HDS in RE-free TM-based synthetic ferrimagnets can enable breakthroughs for numerous applications since it exploits materials that are currently used in magnetic data storage, memories and logic technologies. In addition, this materials study of AO-HDS offers valuable insight into the underlying mechanisms involved. Indeed the common denominator of the diverse structures showing AO-HDS in this study is that two ferromagnetic sub-lattices exhibit magnetization compensation (and therefore angular momentum compensation) at temperatures near or above room temperature. We are highlighting that compensation plays a major role and that this compensation can be established at the atomic level as in alloys but also over a larger nanometers scale as in the multilayers or in heterostructures. We will also discuss the potential to extend AO-HDS to new classes of magnetic materials. This work was done in collaboration with S. Mangin, M. Gottwald, C-H. Lambert, D. Steil, V. Uhl\'i\v{r}, L. Pang, M. Hehn, S. Alebrand, M. Cinchetti, G. Malinowski, Y. Fainman, and M. Aeschlimann. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G7.00002: Domain Structures and Anisotropy in Exchange-coupled [Co/Pd]-NiFe and [Co/Ni]-NiFe Multilayers Larysa Tryputen, Sunjae Chung, Majid Mohseni, T.N. Anh Nguyen, Johan {\AA}kerman, Feng Guo, Robert D. McMichael, Caroline A. Ross Exchange-coupled multilayers [Co/Pd]$_{5}$-/NiFe and [Co/Ni]$_{4}$-NiFe with strong perpendicular magnetic anisotropy have been proposed to use in spin-torque switching and oscillators devices with tilted fixed and free layer to improve their functional performance. We present an experimental study of the magnetization behavior of [Co/Pd]$_{5}$-/NiFe and [Co/Ni]$_{4}$-NiFe multilayers measured using magnetometry, magnetic force microscopy (MFM) and ferromagnetic resonance (FMR) as a function of the thickness of the top NiFe layer. We varied the thickness of the NiFe layer in [Co/Pd]$_{5}$-NiFe (t), t $=$ 0 - 80 nm and [Co/Ni]$_{4}$-NiFe (t), t $=$ 0.5 - 2.5 nm in order to study the interplay between perpendicular magnetization of the Co/Pd or Co/Ni multilayers and in-plane magnetization of the NiFe. Our magnetometry and FMR data suggest that the [Co/Ni]$_{4}$/NiFe multilayer behaves like a homogeneous ferromagnetic film with anisotropy that reorients towards in-plane as the NiFe thickness increases, whereas the [Co/Pd]$_{5}$/NiFe multilayer reveals more complex behavior in which the [Co/Pd] layer retains out-of-plane anisotropy while the magnetization of NiFe layer tilts in-plane with increasing thickness. MFM showed that domains with $\sim$0.1 $\pm$m size were visible in [Co/Pd]-/NiFe with NiFe thickness of 20-80 nm. Multilayers were patterned into sub-100 nm dots using ion beam etching and their magnetization behavior are compared with unpatterned films. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G7.00003: Magnetic anisotropies in epitaxial Py/FeMn/Ni/Cu[001] films Ali Tan, Jia Li, Elke Arenholz, Zi Qiang Qiu The interaction between ferromagnetic and antiferromagnetic layer in a FM/AFM bilayer depends on the details of the spin configurations at the interface. By inserting a Ni layer of different thicknesses below FeMn in Py/FeMn/Cu(001) FM/AFM bilayer, we compared the effect of in-plane and out-of-plane magnetization on the FeMn spin structure which will subsequently influence Py/FeMn interfacial interaction. The Py/FeMn interface interaction is characterized by measuring four-fold and two-fold anisotropies of Py using rotating magneto-optic Kerr effect as a function of Ni and FeMn thicknesses. We found that out-of-plane Ni magnetization has little effect on the Py magnetic anisotropy, but in-plane Ni magnetization enhances the Py magnetic anisotropy in the region just above antiferromagnetic transition thickness. The underlying mechanism could be attributed to the FeMn 3Q spin structure [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G7.00004: Field Dependent Phase Front in Ni[1-x]Cu[x] Graded Alloy Films B.J. Kirby, H.F. Belliveau, D.D. Belyea, C.W. Miller For heterostructures composed of distinct, homogeneous layers, the magnetic properties of the individual layers can be strongly affected by interlayer exchange coupling, leading novel and useful properties (exchange bias, GMR, etc.). Less well understood are structures exhibiting a gradient in magnetic properties, with no discrete interfaces. Particularly interesting is the case where a phase transition is expected across the length of the gradient - do individual regions behave as they would in isolation, or does exchange coupling cause a single phase? Ni[1-x]Cu[x] alloy is a useful model system for, as the Curie temperature (Tc) varies with x. We have studied a 100 nm Ni[1-x]Cu[x] film with x that varies smoothly from 0.39-0.30 across the thickness. Magnetometry measurements of homogenous x=0.39 (x=0.30) samples reveal Tc near 200 K (300 K). Polarized neutron reflectometry measurements of the graded sample magnetic depth profile reveal a distribution of Tc, demonstrating that the sample is not completely coupled. At 300 K we observe evidence of a non-magnetized / magnetized boundary that moves vertically with applied field. Implications of a spatially controllable paramagnetic-ferromagnetic phase boundary will be discussed. Work at USF was supported by NSF-CAREER. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G7.00005: Coercivity Enhancement in V$_{2}$O$_{3}$/Ni Bilayers Siming Wang, Jose de la Venta, Thomas Saerbeck, Juan Gabriel Ramirez, Ivan K. Schuller We studied the temperature dependence of the coercivity and magnetization of V$_{2}$O$_{3}$/Ni bilayers. When the V$_{2}$O$_{3}$ is in the middle of the metal to insulator transition, we observe a maximum enhancement of the coercivity and a decrease of the magnetization. The maximum value of the coercivity shows a 300{\%} increment compared to the room temperature value. The decrease of the magnetization indicates magnetic domain formation. We propose a model in which the inhomogeneous V$_{2}$O$_{3}$ phase transition induces nanoscale stress and disorder in the Ni film. The local stress anisotropy and disorder break the Ni film into magnetic domains and pin the domain walls in Ni. The model is supported by micromagnetic simulations and shows that magnetic properties of ferromagnetic films are strongly affected by the proximity to materials that undergo inhomogeneous phase transition at nanoscale. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G7.00006: PNR studies of spin-flop and spin-flip processes in magnetic multilayer, NiFe/Ir system Haile Ambaye, Gary Mankey, Valeria Lauter, Jimmy Hwang Early GMR devices relied on antiferromagnetic interlayer coupling to work and it was shown that the interlayer coupling is in fact oscillatory, with both ferromagnetic and antiferromagnetic interlayer exchange depending on the thickness of the nonmagnetic layer [1,2]. Different competing interactions such as magnetic anisotropy and interlayer afm coupling occur in multilayer systems. Distinguishing the individual contributions is one of the major challenges in the study of multilayered systems. We used polarized neutron reflectivity (PNR) with full polarization analysis to understand how the magnetization is distributed through the system and how deep the flipping process of the magnetization goes into the system. Depending on the range of the external field applied parallel to the easy axis we studied the occurrence of spin-flop and spin-flip events in the system. \\[4pt] [1] S. S. P. Parkin, Phys. Rev. Lett. \textbf{71}, 1641 (1993).\\[0pt] [2] D. Elefant, et al., Phys. Rev. B \textbf{77}, 014426 (2008). [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G7.00007: Growth of Co/Ni Multilayers with Perpendicular Magnetic Anisotropy N. Soriano, M.H. Kilinc, H.F. Belliveau, C. Redondo, D. Navas, C. Garcia, R. Morales, Casey W. Miller Thin films with perpendicular magnetic anisotropy (PMA) have attracted wide interest for perpendicular recording media applications as well as for devices based on the spin transfer torque effect. In particular, Co/Ni multilayers with strong PMA have been considered one of the most promising candidates for these applications [1]. Understanding the elements which determine the preferred orientation of magnetization in these multilayers involves the study of several factors such as Co/Ni thicknesses, number of bilayers, deposition conditions (base and deposition pressure) and the material and thickness of the underlayer [2]. In this work, we outline our fabrication methods for ultrathin Co/Ni multilayers with a thickness ratio of 1:2 and 1:3 by sputtering at room temperature and using Cu as underlayer. The magnetic behavior of the samples was characterized by polar and transverse magneto optical Kerr effect magnetometer and structural studies were made by X-ray diffractometry.\\[4pt] [1] Guangzhong Wang et al., J. Appl. Phys. 113, 17C111 (2013).\\[0pt] [2] F.J.A. den Broeder, E. Janssen, W. Hoving and W.B. Zeper, IEEE Trans. Magn., 28, 2760 (1992). [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G7.00008: Exchange coupling in MnBi/Fe-Co thin film bilayers Lei Fang, Tieren Gao, Sean Fackler, Shingo Maruyama, Ichiro Takeuchi, Jun Cui, M.J. Krammer, Duane Johnson, Elke Arenholz, Julie Borchers, Brian Kirby, William Ratcliff, Ralph Skomski, Samuel Lofland To achieve enhanced energy products of MnBi for rare-earth free permanent magnet applications, we studied the exchange coupled soft/hard bilayers based on MnBi films. By using DC magnetron sputtering, we fabricated pure MnBi films with magnetization of 500 emu/cc and coercivity of 1.6 T. A (BH)$_{\mathrm{max}}$ of 6.2 MGOe is obtained for pure MnBi films. A large enhancement in (BH)$_{\mathrm{max}}$ due to exchange coupling in MnBi/Fe-Co bilayers is observed with Fe-Co thicknesses between 2 and 5 nm. The highest (BH)$_{\mathrm{max}}$ obtained is 14.0 MGOe at room temperature with a single phase magnetization curve for a MnBi (20 nm)/Co (2 nm) bilayer. TEM and XPS studies indicate there is no oxidation between soft/hard interface. The XMCD results show that the soft moments of Fe/Co at a thickness of 2 nm are perpendicular to the MnBi plane, indicating nearly perfect hard-soft coupling. Moreover, a micromagnetic calculation on perpendicularly-coupled MnBi/Fe-Co bilayers suggests a critical coupling thickness of 4 nm of the soft layer. We will also discuss results from polarized neutron reflectometry measurements performed on the bilayers. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G7.00009: Effects of strain and surfaces on the antiferromagnetic and ferromagnetic phases of thin film FeRh Frances Hellman, Catherine Bordel, Chloe Baldasseroni, Cory Antonakos, Oliver Schneider, Gunar Pal, Sergio Valencia, Akin Unal, Florian Kronast, Slavo Nemsak, Chuck Fadley, Julie Borchers, Brian Maranville FeRh undergoes an unusual antiferromagnetic (AFM) to ferromagnetic (FM) first order transition just above room temperature. This transition can be tuned by pressure, magnetic field, composition, and strain. The underlying source of the transition is still under much discussion, but it is clear from a variety of measurements that electronic structure, lattice, and magnetic excitations all play roles in contributing the underlying entropy difference and hence the competition between AFM and FM states. The surface and bottom interface of thin films are often found to be FM even while the bulk of the film is AFM. The source of this effect, along with the dependence of strain on both anisotropy and transition temperature will be presented and discussed. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G7.00010: Local Atomic Structure and Magnetism in Amorphous Fe$_{\mathrm{x}}$Si$_{\mathrm{1-x}}$ Thin Films Frances Hellman, Yanning Zhang, Catherine Bordel, Kevin Stone, Catherine Jenkins, David Smith, J. Hu, Ruqian Wu, Steve Heald, Jeff Kortright, Julie Karel Amorphous FexSi1-x thin films exhibit a large enhancement in M compared to crystalline films with the same composition (0.45\textless $x$\textless 0.75). XMCD shows enhancement in both spin and orbital moments. Density functional theory (DFT) calculations reproduce this enhanced magnetization. DFT and EXAFS show the amorphous materials have decreased number of nearest neighbors and reduced number density relative to crystalline samples of same x, which leads to the enhanced moment. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G7.00011: Pulsed Laser Deposition of Thin Films of Binary Compounds of Gd and Si using Femto-Second Laser Ravi Hadimani, Yaroslav Mudryk, Timothy Prost, Vitalij Pecharsky, Karl Gschneidner, David Jiles Growth of thin films of Gd$_{5}$(Si$_{\mathrm{x}}$Ge$_{\mathrm{1-x}})_{4}$ has not been reported widely because of difficulty in obtaining the monoclinic phase that is responsible for the giant magnetocaloric effect. Our previous attempt resulted in multiple phases of the material in the film including oxides of Gd [1]. In this work, we therefore report growth of thin films of binary compounds of Gd and Si with Pt protection on top to prevent the oxidation. We have used femto-second laser that results in finer particle size and a composition closer to the target. Microstructure analysis using SEM, EDS was carried out to determine the film thickness, morphology and composition. Magnetic moment vs. temperature measurements were carried out at an applied field of 1000 Oe. The sample showed a major transition below 150~K and a minor transition around 335~K similar to the bulk sample. Magnetization measurements showed that the magnetization in the film saturated close to a field of 5kOe (0.397MA/m). References: [1] R. L. Hadimani, I. C. Nlebedim, Y. Melikhov, D. C. Jiles, ``Growth and characterisation of Gd$_{5}$(Si$_{\mathrm{x}}$Ge$_{\mathrm{1-x}})_{4}$ thin film'' \textit{J.Appl. Phys.}, 113, 17A935, (2013). [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G7.00012: A study of magnetic proximity effect in two-dimensional heterostructure Shanshan Su, Gen Yin, Darshana Wickramaratne, Mahesh Neupane, Roger Lake Recent research found the spin Hall effect and the inverse spin Hall effect in heterostructures composed of a ferromagnetic insulator, Y$_{\mathrm{3}}$Fe$_{\mathrm{5}}$O$_{\mathrm{12}}$, and transition metals with large atomic numbers [1]. It is also reported that graphene has an exchange-splitting with an adjacent EuO layer in both experiments and simulations [2, 3]. Our systems of interest are two-dimensional (2D) heterostructures composed of ferromagnetic insulators, ferromagnetic alloys, and graphene. Along the heterointerface, overlap of the wavefunctions of the ferromagnetic material and graphene leads to a proximity effect. To understand this magnetic proximity effect, density functional theory (DFT) is used. Exchange parameters, magnetic moments, magnetocrystalline anisotropy and exchange-splitting are calculated for the 2D heterostructures. \\[4pt] [1] S. Y. Huang, et. al. Phys. Rev. Lett., \textbf{109}, 107204 (2012).\\[0pt] [2] H. X. Yang, et. al. Phys. Rev. Lett., \textbf{110}, 046603 (2013).\\[0pt] [3] A. G. Swartz, et. al. J. Vac. Sci. Technol. B, \textbf{31}, 04D105 (2013) [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G7.00013: Electric-field-induced modification in magnetocrystalline anisotropy, exchange interaction, and Curie temperature of transition-metal thin films K. Nakamura, M. Oba, T. Akiyama, T. Ito, M. Weinert, A.J. Freeman Magnetism induced by an external electric field ($E$-field) has received much attention as a potential approach for controlling magnetism at the nano-scale with the promise of ultra-low energy power consumption. For magnetocrystalline anisotropy (MCA) in transition-metal thin films, it is agreed that a change in the screening charge density due to an $E$-field, which causes a small change in band structures around Fermi energy, gives rise to a modification of the MCA energy.\footnote{Nakamura et.al, PRL{\bf 102}, 187201(2009); PRB{\bf 81}, 220409(2010)} Here, we extend our first-principles investigation to Curie temperature of an Fe monolayer in an $E$-field. Calculations were carried out using film-FLAPW method that treats spin-spiral structures in an $E$-field. Results predict that when the $E$-field is introduced, calculated magnon (spin-spiral formation) energy is modified, by a few tens of meV, compared to that in zero field. The exchange parameters within the classical Heisenberg model, by making the back Fourier transformation of the magnon energy, suggest the $E$-field-induced modification of Curie temperature. Taking a large MCA energy of the monolayer into account, the modification of Curie temperature by the $E$-field was demonstrated by Monte Carlo simulations. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700