Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Z7: Focus Session: Magnetostructural Properties of Materials |
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Sponsoring Units: GMAG Chair: Luqiao Liu, IBM Research Room: 106 |
Friday, March 7, 2014 11:15AM - 11:51AM |
Z7.00001: Pathways for tailoring the magnetostructural behavior of FeRh-based systems Invited Speaker: Radhika Barua The prediction of phase transition temperatures in functional materials provides dual benefits of supplying insight into fundamental drivers underlying the phase transition, as well as enabling new and improved technological applications that employ the material. In this work, studies focused on understanding the magnetostructural phase transition of FeRh as a function of elemental substitution, provides guidance for tailoring phase transitions in this compound, with possible extensions to other intermetallic-based magnetostructural compounds. Clear trends in the magnetostructural temperatures ($T_{t})$ of alloys of composition Fe(Rh$_{1-x}$M$_{x})$ or (Fe$_{1-x}$M$_{x})$Rh (M $=$ 3$d$, 4$d$~or 5$d$~transition metals), as reported in literature since 1961, were identified and confirmed as a function of the valence band electron concentration (($s+d)$ electrons/atom) of the system. It is observed that substitution of 3$d $or 4$d $elements ($x\le $ 6.5 at{\%}) into B2-ordered FeRh compounds causes $T_{t} $to increase to a maximum around a critical valence band electron concentration ($e_{v}*) $of 8.50 electrons/atom and then decrease. Substitution of 5$d $elements echoes this trend but with an overall increase in $T_{t} $and a shift in $e_{v}* $to 8.52 electrons/atom. For $e_{v} $\textgreater 8.65 electrons/atom, FeRh-based alloys cease to adopt the B2-ordered crystallographic structure in favor of the chemically disordered A1-type structure or the ordered L1$_{0}$-type structure. This phenomenological model has been confirmed through synthesis and characterization of FeRh alloys with Cu, Ni and Au additions. The success of this model in confirming existing data trends in chemically-substituted FeRh and predicting new composition-transition temperature correlations emphasizes the strong interplay between the electronic spin configuration, the electronic band structure, and crystal lattice of this system. Further these results provide pathways for tailoring the magnetostructural behavior and the associated functional response of FeRh-based systems for potential technological applications. [Preview Abstract] |
Friday, March 7, 2014 11:51AM - 12:03PM |
Z7.00002: Hysteretic properties of Nd2Fe14B-based permanent magnets: First principles and micromagnetic modeling Aleksander Wysocki, Denis Kukusta, Liqin Ke, Vladimir Antropov We combine ab initio electronic structure calculations with micromagnetic simulations to investigate permanent magnet properties of Nd2Fe14B-based systems. First, magnetic moments, anisotropy constants and exchange interactions of bulk Nd2Fe14B are calculated from first principles. These parameters are then used to construct a micromagnetic model for realistic samples and evaluate hysteresis loop at finite temperatures using Monte Carlo method. Several generic microstructures are considered including randomly oriented grains, hard/soft multilayers, and core/shell geometries. We find optimal grain sizes and hard phase/soft phase volume ratio which maximize maximum energy products of the systems. Further, we discuss the nature of the thermal spin reorientation effect in the bulk material and how it affects the finite temperature hysteretic properties. [Preview Abstract] |
Friday, March 7, 2014 12:03PM - 12:15PM |
Z7.00003: Mechanochemical synthesis of submicron sized Nd-Fe-B particles using planetary ball mill Ozlem Koylu-Alkan, George C. Hadjipanayis, David J. Sellmyer Mechanochemical synthesis of Nd$_{2}$Fe$_{14}$B particles with size below 0.5 $\mu$m is done via planetary ball mill, followed by annealing of rare-earth oxides, iron oxide and boron oxide in the presence of a reducing agent (Ca) and a dispersant material (CaO). Compared to high energy ball mill, planetary mill gives a range in milling energy. Our purpose is to control the particle size and size distribution by changing the milling energy. In preliminary work, annealed particles in the CaO dispersant with coercivity 4.7 kOe were produced. After washing off the dispersant due to the interstitial modification of 2:14:1 phase with hydrogen, coercivity of the particles was decreased to 1.2 kOe. Electron micrographs of the samples showed that rectangular Nd$_{2}$Fe$_{14}$B particles are present with size distribution in the submicron range. The aim of this study is to obtain nanoparticles with a size below 500 nm and study the effect of size and surface on their magnetic properties. Work supported by DOE DE-FG02-04ERU612. [Preview Abstract] |
Friday, March 7, 2014 12:15PM - 12:27PM |
Z7.00004: Influence of grain size on precipitation hardening in melt-spun Sm(Co, Fe, Cu, Zr)$_{\mathrm{z}}$ alloys Ozlem Koylu Alkan, Weiqiang Liu, Xiaocao Hu, George C. Hadjipanayis In this work, we have investigated the influence of grain size on precipitation hardening that takes place in 2:17 Sm-Co magnets. An alloy with a nominal composition of Sm(Co$_{0.72}$Fe$_{0.12}$Cu$_{0.13}$Zr$_{0.03})_{7.6}$ was prepared by arc-melting and subsequently melt-spinning. The grain size was controlled by varying the wheel speed from 5 m/s to 50 m/s. The melt-spun ribbons were subsequently isothermally aged at 850 $^{\circ}$C for 3 h followed by slow cooling at 0.7 K/min to 400 $^{\circ}$C. A single 1:7 phase was detected in the as-spun ribbons and the grain size of ribbons estimated by Scherrer's formula was found to decrease gradually with the increasing of the wheel speed from 5 m/s to 50 m/s. After aging, the 1:7 phase was decomposed into Sm$_{2}$(Co,Fe)$_{17}$ and Sm(Co,Cu)$_{5}$ phase. For the 5 m/s ribbon, the coercivity increased drastically form 0.8 kOe to 11.2 kOe. On the other hand, the coercivity of the 35 m/s ribbon showed a little increase from 4.7 kOe to 6.3 kOe. TEM studies are currently under way to study the microstructure as a function of grain size and the results will be reported. [Preview Abstract] |
Friday, March 7, 2014 12:27PM - 12:39PM |
Z7.00005: Principle of Magnetodynamics for Composite Magnetic Pole Alexander Animalu It is shown in this paper that geometry provides the key to the new \textit{magnetodynamics} principle of operation of the machine (invented by Dr. Ezekiel Izuogu) which has an unexpected feature of driving a motor with static magnetic field. Essentially, because an array of like magnetic poles of the machine is arranged in a half circular array of a cylindrical geometry, the array creates a non-pointlike magnet pole that may be represented by a ``magnetic current loop'' at the position of the pivot of the movable arm. As a result, in three-dimensional space, it is possible to characterize the symmetry of the stator magnetic field \textbf{B} and the magnetic current loop \textbf{J} as a cube-hexagon system by a 6-vector (\textbf{J},\textbf{B}) (with \textbf{J}.\textbf{B}$\ne $\textbf{0)} comprising a 4x4 antisymmetric tensor analogous to the conventional electric and magnetic 6-vector \textbf{(E,B}) (with \textbf{E}.\textbf{B}$\ne $\textbf{0)} comprising the 4x4 antisymmetric tensor of classical electrodynamics The implications are discussed. [Preview Abstract] |
Friday, March 7, 2014 12:39PM - 12:51PM |
Z7.00006: Magnetic domain formation in field-cooled metals Dirk Wulferding, Doohee Cho, Il Kyu Yang, Yoon Hee Jeong, Ji Ho Sung, Moon-Ho Jo, Han Woong Yeom, Jeehoon Kim We explore the effect of field-cooling on the formation of magnetic domains in films of the magnetic metals Ni and Fe using magnetic force microscopy. In particular, we study the dependence of the domain pattern on both film thickness and external magnetic field strength and compare the results to the domain structures of zero-field cooled specimens. [Preview Abstract] |
Friday, March 7, 2014 12:51PM - 1:03PM |
Z7.00007: Thermodynamic Stability of ThMn$_{12}$-type CeFe$_{8}$M$_{4}$ Magnetic Compounds J.F. Herbst, Chen Zhou, F.E. Pinkerton Rare earth (R) elements such as Nd and Dy are critical constituents of high-performance Nd$_{2}$Fe$_{14}$B-type permanent magnets. Ongoing economic uncertainties have stimulated great interest in magnets that use alternative R materials, Ce in particular since it is the most abundant R element. While the intrinsic magnetic properties of known Ce-based compounds are inferior to those of their Nd-based cognates, they nevertheless offer the prospect of developing magnets with technical characteristics intermediate between those of Nd-Fe-B and ferrites. Moreover, there is ample opportunity to identify novel Ce systems. As a means of guiding the synthesis of new CeFe$_{\mathrm{12-x}}$M$_{\mathrm{x}}$ phases we have assessed the thermodynamic stability of ThMn$_{12}$-type CeFe$_{8}$M$_{4}$ compounds with 26 different elements M via density functional calculations. Compounds of this class are attractive since they can have larger Fe:R ratios than R$_{2}$Fe$_{14}$B, and in some cases additional processing such as nitriding, hydriding, or carbiding can substantially improve the magnetic properties. We critically compare the theoretical results with experiment. [Preview Abstract] |
Friday, March 7, 2014 1:03PM - 1:15PM |
Z7.00008: Magnetic Field Dependent Phase Boundaries in Al-Cu alloys up to 35 Tesla Jason Cooley, Seth Imhoff, Martha Katz We report on the magnetic field dependence of the liquid-solid phase boundary in the Al-Cu alloy system between 0 and 17 at. {\%} Cu at fields up to 35 Tesla. Melting/freezing point measurements were performed using a purpose built Differential Thermal Analysis instrument capable of operating in the 32 mm bore of a 35T Bitter magnet at the National High Magnetic Field Laboratory DC Field facility in Tallahassee Florida. In general the application of field increases the melting point by approximately 10 degrees Celsius. [Preview Abstract] |
Friday, March 7, 2014 1:15PM - 1:27PM |
Z7.00009: Effect of Co doping on the structural, magnetic and electron transport properties of Mn$_{2}$PtSn Heusler alloy Parashu Kharel, Yung Huh, Austin Nelson, Valloppilly Shah, Ralph Skomski, David Sellmyer Materials with high magnetic anisotropy and Curie temperature well above room temperature have huge potential for a range of applications including permanent magnet, high density recording and spintronic devices. Tetragonal Mn$_{2}$PtSn is one such Heuslar compounds which has been predicted to have very high magnetic anisotropy but its low Curie temperature (T$_{\mathrm{c}}=$ 374 K) is a drawback [1]. Our experimental investigation of the rapidly quenched nanostructured ribbons shows that a single phase Mn$_{2}$PtSn in the tetragonal structure cannot be easily prepared without the substitution of an external element. We have found that a partial replacement of Pt with Co in Mn$_{2}$PtSn stabilizes the tetragonal structure and also improves the magnetic properties. The experimentally observed values of the room-temperature saturation magnetization (M$_{\mathrm{s}}$) and Curie temperature (T$_{\mathrm{c}}$) are respectively 35 emu/g and 385 K for Mn$_{2}$PtSn and 43 emu/g and 516 K for Mn$_{2}$Pt$_{0.3}$Co$_{0.7}$Sn. The effect of cobalt on the magnetic anisotropy and electron transport properties of this material will be discussed.\\[4pt] [1] J. Winterlik et al., Adv. Mater. \textbf{24}, 6283 (2012). [Preview Abstract] |
Friday, March 7, 2014 1:27PM - 1:39PM |
Z7.00010: Magnetic, Electrical and Structural study of Mn-Co-Sn Heusler Nanomaterials Yung Huh, P. Kharel, A. Nelson, V. Shah, R. Skomski, D. Sellmyer The nano-structured Mn$_{3-x}$Co$_{x}$Sn (x = 0, 0.3, 0.5, 0.7, 1.0) alloys were prepared using arc-melting, melt-spinning and thermal annealing. Mn$_{3}$Sn is stable in the hexagonal structure and it shows an antiferromagnetic spin order at room temperature. Mn$_{3-x}$Co$_{x}$Sn alloys maintained a hexagonal structure upon substituting Mn with Co up to x = 0.7, and then it transformed to cubic phases at x = 1.0. At room temperature Mn$_{3-x}$Co$_{x}$Sn (x = 0.5, 0.7, 1.0) exhibited ferromagnetic spin order. Mn$_{2.3}$Co$_{0.7}$Sn sample showed Curie temperature of 640 K. However, the transition temperatures are suppressed to 600 K for Mn$_{2.5}$Co$_{0.5}$Sn and Mn$_{2.0}$Co$_{1.0}$Sn. The room temperature saturation magnetization measured at 7.0 T increases with increasing amount of Co substitution, varying from 13 emu/g (x = 0.5), 25 emu/g (x = 0.7), and 50 emu/g (x = 1.0), respectively. The electrical resistivity of all the Co-substituted samples depends on temperature and decreases with increasing temperature from 5 K to room temperature. Interestingly, there observed a rapid upturn in the resistivity at 250 K for Mn$_{2.5}$Co$_{0.5}$Sn. [Preview Abstract] |
Friday, March 7, 2014 1:39PM - 1:51PM |
Z7.00011: Magnetic properties of the off-stoichiometric Heusler alloys Ni$_{50-x}$Co$_{x}$Mn$_{40}$Sn$_{10}$ using $^{55}$Mn NMR as a local probe Shaojie Yuan, Philip Kuhns, Michael Hoch, James Brooks, Arneil Reyes, Vijay Srivastava, Daniel Phelan, Richard James, Chris Leighton The off-stoichiometric Heusler-type alloys Ni$_{50-x}$Co$_{x}$Mn$_{40}$Sn$_{10}$ have interesting properties and a rich phase diagram, stemming from the interplay between magnetic order, martensitic transformations, and ferroelasticity. Previous magnetization and small angle neutron scattering (SANS) measurements suggest that at low temperatures ferromagnetic (F) nanoscale clusters and antiferromagnetic (AF) regions coexist. As the temperature is raised above 50-100 K the F regions undergo superparamagnetic blocking while the AF matrix is thought to persist to higher temperatures. We have applied zero and low field nuclear magnetic resonance as a local probe to determine the temperature and field dependent behavior of the F and AF components for samples with x = 0, 7 and 15. For x = 7 evidence is obtained for two distinct Mn electronic environments which are characterized by different hyperfine fields. In addition, detailed information has been obtained on the evolution with temperature of the F and AF components. Results obtained for the x = 0 and x = 15 samples help to determine the nature of the ground state in these systems. A model which can account for the magnetic properties of the material will be presented, together with a modified phase diagram. [Preview Abstract] |
Friday, March 7, 2014 1:51PM - 2:03PM |
Z7.00012: ABSTRACT WITHDRAWN |
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