Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D54: Structural and Mechanical Properties of Correlated Electron Magnets |
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Sponsoring Units: GMAG Chair: Dylan T. Grandmont, University of Alberta Room: Mile High Ballroom 1B |
Monday, March 3, 2014 2:30PM - 2:42PM |
D54.00001: Nanomechanical Detection of Radio Frequency AC Susceptibility in Individual Thin Permalloy Elements Dylan T. Grandmont, Joseph E. Losby, Lance C. Parsons, Fatemeh Fani Sani, Mark R. Freeman, Gregory E. Bridges, Kaveh Mohammad, Elham Salimi, Douglas J. Thomson We report a new method for RF AC susceptometry in individual mesoscopic permalloy elements fabricated onto nanomechanical torque resonators. The technique involves the mixing of orthogonal AC magnetic field excitations to yield net magnetic torques at difference frequencies corresponding to torsional mechanical resonances. Simultaneous detection of both DC and frequency-dependent signatures through multi-frequency lock-in detection is possible, allowing for the separation of reversible responses as a function of field. The measurements can be conducted at room temperature with high applied fields, and extended to be sufficiently broadband to complement existing techniques for probing magnetization dynamics. [Preview Abstract] |
Monday, March 3, 2014 2:42PM - 2:54PM |
D54.00002: Nanomechanical AC Susceptometry of an Individual Mesoscopic Ferrimagnet Joseph Losby, Zhu Diao, Fatemeh Fani Sani, Dylan Grandmont, Miro Belov, Jacob Burgess, Wayne Hiebert, Mark Freeman A new method for simultaneous detection of both DC and time-dependent magnetic signatures in individual mesoscopic structures has emerged from early studies in spin mechanics. Multifrequency nanomechanical detection of AC susceptibility and its harmonics highlights reversible nonlinearities in the magnetization response of a single yttrium iron (YIG) element, separating them from hysteric jumps in the DC magnetization. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D54.00003: Complex magnetic properties in multilayer rare earth oxypnictides Jiakui Wang, Andrea Marcinkova, Chih-Wei Chen, Emilia Morosan Intensive research interest on layered transition metal pnictide materials was stimulated by the discovery of high temperature superconductivity in Fe-pnictides a few years ago. To study the relationship between superconductivity, crystal structure and magnetism, and to search for novel superconductors of better application potential, more transition metal pnictides are worth investigating. In this talk, I will discuss physical properties of members of a particular class of layered oxypnictides, with four transition metal pnictogen layers per unit cell. While varying the rare earth ion, we find that one compound is a low temperature superconductor (Tc ~ 1.7 K), and others show diverse magnetic properties, including ferromagnetic or antiferromagnetic order, or spin glass behavior. I will show our observation from measurements of DC and AC magnetization, specific heat and resistivity. The understanding of the physical properties of these isostructual compounds may serve as a guide in the search for superconductivity in these systems. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D54.00004: Effect of Grain Size on Spinodal Decomposition and Magnetic Properties in Melt-Spun Alnico Alloys George Hadjipanayis, Bianca Frincu, Konrad L\"owe, Xiaocao Hu, Oliver Gutfleisch The low coercivity of Alnico magnets, which develops upon spinodal decomposition, limits their use for high temperature applications. The aim of this work is to investigate the effect of grain size on the spinodal decomposition in Alnico melt-spun alloys and hopefully be able to tailor the spinodal structures by varying the grain size and processing routes to include magnetic annealing that may lead to higher coercivity. The grain size of the samples was varied by changing the wheel speed from 5-60 m/s. Spinodal decomposition was induced by subjecting the samples to an annealing heat treatment at temperatures in the range of 600-900 C The spinodal structures were observed in micron size grains with a spinodal size in the range 45-80 nm with the larger size corresponding to the higher wheel speed samples. The coercivity was also found to depend strongly on the size of spinodal structures with the highest value obtained in the sample with the finer spinodal size. We are currently continuing our studies in ribbons with submicron size grains and the results will be reported. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D54.00005: Origin of Martensitic Phase Transitions in Thin Films of Ni-Mn-In on MgO Substrate Renat Sabirianov, Andrei Sokolov, Nabil Al-Aqtash We study the impact of the substrate on the martensite transformation of Ni-Mn-In thin films using density functional theory calculations. Our calculation of bulk Ni$_{2}$Mn$_{1.5}$In$_{0.5}$ alloy shows that the cubic phase is unstable against the tetragonal distortion phase and undergoes the martensitic transformation to form tetragonal martensite in ferrimagnetic state. Ni$_{2}$Mn$_{1.5}$In$_{0.5}$ thin films (in both cubic and tetragonal phases) on MgO (001) substrates are studied. The presence of MgO substrate changes the relative stability of ferrmomagnetic (FM) austenite and ferrimagnetic (FiM) martensite states. The energetically favorable structures of the MgO-Ni$_{2}$Mn$_{1.5}$In$_{0.5}$ systems depend on the lattice parameters. Our calculations show that the energy difference between FM austenite and FiM martensite states in 12 layers of Ni$_{2}$Mn$_{1.5}$In$_{0.5}$ film on MgO (001) substrate is ($\Delta $E $=$ 0.08eV) per NiMnIn f.u, compared to ($\Delta $E $=$ 0.24eV) in the bulk at the same lattice parameters. When the lattice parameters of 12 layers of Ni$_{2}$Mn$_{1.5}$In$_{0.5}$ film have values close to those of MgO substrate, this energy difference become ($\Delta $E $=$ -0.16eV) per NiMnIn f.u. These results clearly indicate the possibility of control of martensitic transition in thin films by substrate. We compare our results with the magnetic and transport measurements performed on the thin films of Ni$_{50}$Mn$_{35}$In$_{15}$ grown by laser-assisted molecular beam epitaxy deposition. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D54.00006: Effect of displacement damages on physical properties of amorphous TbFeCo thin films Jiwei Lu, Tom Anuniwat, Xiaopu Li, Joe Poon, Brad Weaver The ferrimagnetism in amorphous rare-earth transition metal alloys is well known, and has recently been investigated for applications in perpendicular magnetic random access memory (p-MRAM), which is considered to be a universal memory technology due to the low power dissipation and the non-volatility. The amorphous TbFeCo (TFC) thin films were deposited by rf magneton sputtering. The as-deposited film exhibited a low saturation magnetization and a high perpendicular anisotropy. Hall bar devices were fabricated for characterizing the magneto-transport behaviors. The proton irradiation, known for creating displacement damages, was to modify the short range ordering in amorphous TFC film. The Stopping and Range of Ions in Matters simulation demonstrates large cascade of rare-earth element during irradiation event that might cause the local structural damage. Both thin film samples and Hall bar devices were exposed to 2 MeV-energy protons with incremental fluences up to 1.9x10$^{15}$ H$^{+}$/cm$^{2}$. We observed the increase in saturation moment and electrical resistance. The irradiated samples exhibit a compensation point below room temperature. The saturated anomalous Hall resistance remained relatively unchanged despite of the increased saturation moment. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D54.00007: Site preference of ternary alloying addition (Ti, Fe, Co and Ni) in DO$_3$ Fe$_3$Al, Co$_3$Al and Ni$_3$Al - basic compound for alnico-8 magnetic materials German Samolyuk, Balazs \'{U}jfalussy, Malcolm Stocks We performed first-principles calculations to investigate the site preference of ternary alloying additions in DO$_3$ Fe$_3$Al, Co$_3$Al and Ni$_3$Al alloys. In Fe$_3$Al the discussed ternary elements are found to occupy the Fe sublattice. For both Fe-rich and Al-rich compounds, the ternary elements with fewer 3$d$ electrons than Fe (Ti) prefer to occupy $\alpha$-sites of Fe sublattice and elements with larger number of 3$d$ electrons - the $\gamma$-sites. In Fe-rich regions, the small enthalpy difference of Ti occupying $\alpha$-sites of Fe and Al sublattices, the site distribution of Ti varies with concentration and temperature. A similar dependency was obtained for Ni distribution between Co and Al sublattice in Co$_3$Al. Similar to the Fe$_3$Al alloy, the ternary element prefer to occupy Co sublattice with a change of preferred sites from $\alpha$ for Ti and Fe to $\gamma$ for Ni. In the Ni-rich Ni$_3$Al the ternary elements prefer to occupy the Al sublattice, while, in the Al-rich alloy the ternary elements prefer to occupy Ni sublattice in a similar fashion. The magnetic moments of transition metals in Fe$_3$Al and Co$_3$Al are ordered ferromagnetically, whereas the Ni$_3$Al is nonmagnetic unless the Fe or Co are added as a ternary element. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D54.00008: Unusual structural evolution in KCuF$_3$ at high temperatures by neutron powder diffraction Luke G. Marshall, Jianshi Zhou, Jianzhong Zhang, Jiantao Han, Sven C. Vogel, Xiaohui Yu, Yusheng Zhao, Maria-Teresa Fernandez-Diaz, Jinguang Cheng, John B. Goodenough High-resolution neutron powder diffraction has been performed to study the structural evolution of the perovskite KCuF$_3$ at temperatures up to 900 K. Results of the Rietveld refinement reveal an unusual site distortion that increases as temperature increases. In contrast to the widely accepted assumption that a cooperative Jahn-Teller transition may occur at 800 K, no phase transition was observed up to 900 K. We have made a comparative study of the Jahn-Teller distortion in fluorides and oxides with variables such as temperature, pressure, and the dilution by non-Jahn-Teller active ions in these compounds. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D54.00009: High-Throughput Magnetization Measurements of Co-Fe-Ni variable composition alloys with a Scanning Hall Probe Microscope Girfan Shamsutdinov, Boris Nadgorny, Peng Zhao, Ji-Cheng Zhao, Sreenivas Bhattiprolu A Scanning Hall Probe Microscope (SHPM) with a submicron Hall probe (HP) was used for high efficiency characterization of Co-Fe-Ni binary and ternary alloys. The Co-Fe-Ni alloys were fabricated by annealing three metal blocks placed in intimate contact at high temperatures to allow thermal interdiffusion to create solid-solution with a composition spread over the binary and the ternary diffusion regions. The change in the magnetic field in the vicinity of these couples and multiples, Fe-Co, Fe-Ni, Co-Ni and Co-Fe-Ni alloys, was measured continuously as the HP was scanned across the interdiffusion regions. Using a simple model we have then determined the corresponding values of saturation magnetizations of the alloys that came out to be in good agreement with the known values for pure Fe, Co and Ni. The composition variations and crystal phase structure over the scan regions were measured independently using Energy Dispersive X-ray Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD). Using this technique, the composition-structure-property relationship for the Co-Fe-Ni diffusion system was determined for the first time. This study demonstrates that Scanning Hall microscopy, in combination with microanalyses techniques, can be effectively applied for high efficiency and high accuracy investigations of composition-structure-property relationship and to accelerated materials design. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D54.00010: Electronic correlations determine the phase stability of iron up to the melting temperature I. Leonov, A.I. Poteryaev, Y.N. Gornostyrev, A.I. Lichtenstein, M.I. Katsnelson, V.I. Anisimov, D. Vollhardt We present results of a theoretical investigation of the phase stability and phonon spectra of paramagnetic iron at high temperatures obtained within the LDA+DMFT scheme. This approach combines {\it ab initio} band-structure methods with dynamical mean-field theory for correlated electrons and allows one to calculate correlation-induced structural transformations and their temperature evolution [1]. We find that electronic correlations determine the structural phase stability of iron up to the melting temperature. Several peculiarities, including a pronounced softening of the [110] transverse $T_1$ mode and a dynamical instability of the $bcc$ lattice in harmonic approximation, are identified. We relate these features to the $\alpha$-to-$\gamma$ and $\gamma$-to-$\delta$ phase transformations in iron. The high temperature $bcc$ phase of iron is found to be highly \textit{anharmonic} and appears to be stabilized by the lattice entropy. This indicates the importance of both electronic correlations and lattice anharmonic effects for a correct description of the high-temperature $\delta$ phase of iron. [1] I.Leonov, A.I.Poteryaev, V.I.Anisimov, D.Vollhardt, PRL {\bf 106}, 106405 (2011); PRB {\bf 85}, 020401 (2012). [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D54.00011: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 4:42PM - 4:54PM |
D54.00012: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 4:54PM - 5:06PM |
D54.00013: Anomalous properties in a rare correlated ferromagnet Nd$_{2}$PdSi$_{3}$ Shanta Saha, Renxiong Wang, Johnpierre Paglione, Jeffrey Lynn The compound Nd$_{2}$PdSi$_{3}$ belongs to an AlB$_{2}$-derived ternary family (hexagonal structure, space group $P$6/\textit{mmm}) showing many exotic properties [1-3]. This compound is considered to order ferromagnetically (\textit{\textless }16 K), unlike other members of this series ordering antiferromagnetically. The magnetic ordering temperature ($T_{0})$ is significantly enhanced with respect to the de Gennes--scaled value [3]. Recently, based on polycrystalline study the effects of Nd (4$f) $hybridization on the magnetism is discussed, which is rare in an Nd-based intermetallic compound [3]. We have grown single crystals of Nd$_{2}$PdSi$_{3}$ using Czochralski method in a tetra arc furnace. We would like to present neutron scattering, transport, magnetic, and thermal properties on Nd$_{2}$PdSi$_{3}$ and discuss Nd (4$f) $hybridization.\\[4pt] [1] S. R. Saha \textit{et al}. , Phys. Rev. B \textbf{60}, 12162 (1999).\\[0pt] [2] S. R. Saha \textit{et al}. , Phys. Rev. B \textbf{62}, 425 (2000). \\[0pt] [3] K. Mukherjee \textit{et al}., Phys. Rev. B, \textbf{84}, 184415 (2011). [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D54.00014: Transport and magnetic properties of Ce$_{1-x}$La$_x$Cu$_2$Ge$_2$ single crystals Halyna Hodovanets, Sergey L. Bud'ko, Valentin Taufour, Hyunsoo Kim, Warren E. Straszheim, Paul C. Canfield We present magnetic-susceptibility, resistivity, heat-capacity, and thermoelectric power measurements on single crystals of La-diluted Kondo lattice CeCu$_2$Ge$_2$. The results of these measurements show that the antiferromagnetic temperature $T_N$ is suppressed in almost linear fashion with increasing of La concentration. The magnetic order was observed from x=0 ($T_N$=4.15 K) up to x=0.80 where $T_N$=0.56 K with 0.38 K being the lowest base temperature in our measurements. The characteristic Kondo temperature was found to decrease from 4 K to 1 K rather slowly. For the lowest concentrations of La, the heat capacity was shown to follow the prediction of the Kondo-impurity model. [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D54.00015: Incommensurate Magnetic Structure of Rare Earth Compounds RCuAs$_2$ Yang Zhao, J.W. Lynn, Gohil S. Thakur, Zeba Haque, L.C. Gupta, A.K. Ganguli The rare-earch intermetallic compounds have been actively studied during the last three decades due to their rich fundamental physical properties. Recently, a new class of compounds with the form of RCuAs$_2$ have been discovered [1]. We carried systematic neutron scattering studies to investigate the magnetic ground states and temperature evolution of the magnetic structures of these compounds. The neutron powder diffraction results unveil complicated incommensurate magnetic structures for the Ho and Tb samples. The inelastic neutron scattering shows a crystal electric field excitation at around 7 meV for both Ho and Tb compounds. We will continue the study of other rare-earth RCuAs$_2$ compounds in the near future. \\[4pt] [1] E. Sampathkumaran, K. Sengupta, S. Rayaprol, K. Iyer, T. Doert, and J. Jemetio, Physical Review Letters 91, 036603 (2003). [Preview Abstract] |
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