Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V28: Functional Magnetic Materials |
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Sponsoring Units: GMAG Chair: Casey Miller, Rochester Institute of Technology Room: 291 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V28.00001: Long-range antiferromagnetic interactions in Ni-Co-Mn-Ga metamagnetic Heusler alloys Fabio Orlandi, Simone Fabbrici, Franca Albertini, Pascal Manuel, Dmitry Khalyavin, Lara Righi The quaternary Ni-Co-Mn-X (X $=$ Ga, Sn, In and Sb) alloys have focused a considerable interest in the field of the multifunctional materials thanks to their remarkable properties, such as giant magnetocaloric and exchange-bias effect, related to an inverse magneto-structural transition. In this talk we will report on the experimental observation of a long-range antiferromagnetic structure in the metamagnetic Ni-Co-Mn-Ga Heusler alloys: a two-step process, featuring the ordering of the Ni and Mn sublattices at different temperatures, establishes the antiferromagnetic structure in martensite. The accurate magnetic symmetry analysis, based on experimental neutron diffraction, allows the determination of the correct magnetic space group of the system. The observation of such spin structure clarifies the current debate on the presence of antiferromagnetic interactions in the (Ni,Co)-Mn-X (X$=$ Ga, Sn, Sb, In) shape memory alloys and opens new insights in the understanding of the magnetostructural properties of this relevant class of materials. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V28.00002: Small-Angle Neutron Scattering Study of Nanoscale Magnetic Inhomogeneity in the Off-Stoichiometric Heusler Ni50-xCoxMn40Sn10 Sami El-Khatib, Vijay Srivastava, Richard D. James, Chris Leighton Off-stoichiometric Heusler alloys of the form Ni50-x\textlnot CoxMn25$+$ySn25-y have attracted much recent interest, from the fundamental perspective due to magnetic phase competition, and from the applied perspective due to potential shape memory, sensor, actuator, and energy conversion applications. Recently we applied Small-Angle Neutron Scattering (SANS) and NMR to this alloy system for the first time, directly observing the separation into interacting ferromagnetic and antiferromagnetic nanoscale spin clusters that explains bulk superparamagnetism and exchange bias. These prior SANS measurements were performed at the representative composition x $=$ 6. In this work we expand this SANS study to x $=$ 2 and 12, spanning the three main regimes in the Ni50-x\textlnot CoxMn25$+$ySn25-y phase diagram. The results provide detailed information on the evolution in magnetic ordering and inhomogeneity with Co doping, most notably the persistence of nanoscale magnetic inhomogeneity even in the non-martensitic region, and the direct evidence found for separation of superparamagnetic and exchange bias blocking temperatures at some compositions. The results are discussed in terms of a compositional fluctuation picture. [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V28.00003: Magnetic entropy changes with zero hysteresis loss in the vicinity of the first-order phase transition in Ni$_{\mathrm{2}}$Mn$_{\mathrm{0.55}}$Co$_{x}$Cr$_{\mathrm{0.45-}}_{x}$Ga Heusler alloys Jeffrey Brock, Mahmud Khan The observation of mitigated drawbacks in a material exhibiting a first-order magnetostructural phase transition near room temperature as well as moderate magnetocaloric effects are pertinent towards the realization of energy-efficient and environmentally-friendly solid state refrigeration technologies. The main drawbacks of a first-order material are hysteresis losses, which dramatically reduce cooling efficiency. Here, we present an experimental study on a set of NiMn$_{\mathrm{0.55}}$Co$_{x}$Cr$_{\mathrm{0.45-}}_{x}$Ga ($x=$ 0, 0.1) Heusler alloys. X-ray diffraction, dc magnetization, and differential scanning calorimetry measurements have been performed on these materials. At room temperature, the alloys were found to crystallize in the tetragonal martensite structure (\textit{P6}$_{3}$\textit{/mcm}). Magnetization measurements showed that both samples exhibited a single first-order magnetostructural phase transition, and that the replacement of Cr with Co shifted the transition temperature from 250 K ($x=$ 0) to 290 K ($x=$ 0.1), while narrowing the thermal hysteresis from 4 K to 1.7 K. Magnetization measurements also revealed that the Co-substituted alloy exhibited near-zero magnetic hysteresis, including near $T_{\mathrm{C}}$. Calorimetric data showed that the first-order magnetostructural phase transition of the Co-substituted alloy had near-perfect reproducibility over many thermal cycles. For a magnetic field change of 0 -- 2 T, the Co-substituted sample exhibited a magnetic entropy change and refrigerant capacity of 3.14 J kg$^{\mathrm{-1}}$ K$^{\mathrm{-1}}$ and 54.54 J kg$^{\mathrm{-1}}$, respectively. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V28.00004: Inverse magnetocaloric effect in metamagnetic In-based alloys at high magnetic fields Sudip Pandey, Yury Koshkid’ko, Elvina Dilmieva, Jacek Cwik, Igor Dubenko, Anil Aryal, Abdiel Quetz, Alexander Granovsky, Erkki Lähderanta, Arkady Zhukov, Shane Stadler, Naushad Ali Magnetocaloric effects (MCE) in Ni$_{\mathrm{50}}$Mn$_{\mathrm{35}}$In$_{\mathrm{15}}$, Ni$_{\mathrm{50.2}}$Mn$_{\mathrm{34.85}}$In$_{\mathrm{14.95}}$,$_{\mathrm{\thinspace }}$and Ni$_{\mathrm{50}}$Mn$_{\mathrm{35}}$In$_{\mathrm{14.25}}$Â$_{\mathrm{0.75}}$ Heusler alloys have been studied through direct measurements of the adiabatic temperature change ($\Delta $T$_{\mathrm{ad}})$ using the extraction method for magnetic field changes up to 14 T. Both the $\Delta $T$_{\mathrm{ad}}$ and the entropy changes ($\Delta $S$_{\mathrm{M}})$ increase as the martensitic transition approaches the Curie temperature of the austenitic phase. The $\Delta $T$_{\mathrm{ad}}$ increases up to a maximum value of 15 K with field and saturates at high fields. The influence of the rate of change of the magnetic field and the rate of heating to the initial temperature before applying field on the $\Delta $T$_{\mathrm{ad}}$ of Ni$_{\mathrm{50}}$Mn$_{\mathrm{35}}$In$_{\mathrm{14.25}}$Â$_{\mathrm{0.75}}$ has been studied. It has been shown that increasing the heating rate from 6 to 22 K/min results in an increase of $\Delta $T$_{\mathrm{ad}}$ by about 40{\%} for $\Delta $H$=$10 T. Acknowledgements: This work was supported by the U.S. Department of Energy, DOE Grant No. DE-FG02-06ER46291 (SIU) and DE-FG02-13ER46946 (LSU). [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V28.00005: Scandium-induced ferromagnetism in gadolinium-based magnetoresponsive materials Durga Paudyal, Y. Mudryk, V. K. Pecharsky Replacement of the strongly magnetic gadolinium atoms with non-magnetic scandium rapidly enhances ferromagnetic interactions in (Gd$_{1-x}$Sc$_{x})_{5}$Ge$_{4}$. This is due to the unique role 3d electron of scandium play in mediating magnetic interactions between the gadolinium atoms from the neighboring layers in the crystal lattice. Our studies confirm that a much higher magnetocaloric effect can be achieved in first-order materials compared to second-order materials of similar structure and composition. Sc concentrations higher than 20{\%} lead to a formation of a closely related Pu$_{5}$Rh$_{4}$-type structure where first order magnetostructural transformation is replaced by a conventional second-order magnetic ordering. This work also demonstrates how a specific structural feature, more precisely specific interatomic distances and exchange interactions can be utilized to predict anomalous physical behaviors in a series of alloys where conventional wisdom suggests a rather trivial continuous solid solubility and usual magnetism. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V28.00006: Development of a New High Strain Magnetostriction Material Aaron Hamann, E Dan Dahlberg A novel magnetostrictive (MS) material that produces reversible strains on the order of 5{\%} will be described. The MS system we developed differs from conventional MS materials in that it is a composite of 0.025 cm diameter carbon steel wires cut to random lengths between 0.3 and 0.6 cm embedded in a soft polymer matrix. Eleven samples were investigated, each with different wire content. Magnetostrictive strains as large as 20{\%} were observed in applied fields of 600 Oe, although these strains were not completely reversible; as stated earlier, the reversible magnetostrictive strains were at least 5{\%}. The physical mechanism responsible for the large MS strains is the rotation of the wires to be parallel with an applied field, causing the polymer matrix to stretch in the direction of the field. This study was a proof of concept and efforts to maximize the strain were not taken. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V28.00007: Giant Magnetoelectric Energy Conversion Utilizing Inter-Ferroelectric Phase Transformations in Ferroics Peter Finkel, Margo Staruch Phase transition-based electromechanical transduction permits achieving a non-resonant broadband mechanical energy conversion see ( Finkel et al Actuators, 5 [1] 2. (2015)) , the idea is based on generation high energy density per cycle , at least 100x of magnitude larger than linear piezoelectric type generators in stress biased [011]cut relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal can generate reversible strain \textgreater 0.35{\%} at remarkably low fields (0.1 MV/m) for tens of millions of cycles. Recently we demonstrated that large strain and polarization rotation can be generated for over 40 x 10$^{\mathrm{6}}$cycles with little fatigue by realization of reversible ferroelectric-ferroelectric phase transition in [011] cut PIN-PMN-PT relaxor ferroelectric single crystal while sweeping through the transition with a low applied electric field \textless 0.18 MV/m under mechanical stress. This methodology was extended in the present work to propose magnetoelectric (ME) composite hybrid system comprised of highly magnetostrictive alloymFe81.4Ga18.6 (Galfenol), and lead indium niobate--lead magnesium niobate--lead titanate (PIN-PMN-PT) domain engineered relaxor ferroelectric single crystal. A small time-varying magnetic field applied to this system causes the magnetostrictive element to expand, and the resulting stress forces the phase change in the relaxor ferroelectric single crystal. ME coupling coefficient was fond to achieve 80 V/cm Oe near the FR-FO phase transition that is at least 100X of magnitude higher than any currently reported values. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V28.00008: Demonstration of Scalable Nernst Voltage in a Coiled Galfenol Wire Emilio Codecido, Zihao Yang, Jason Marquez, Yuanhua Zheng, Joseph Heremans, Roberto Myers Transverse thermopower by the Nernst effect is usually considered far too weak an effect for waste heat recovery and power generation. We propose that magnetostriction provides a pathway to enhance the Nernst effect because it increases phonon and magnon coupling. Here, we measure the Nernst coefficient in the magnetostrictive alloy, Galfenol (Fe$_{\mathrm{0.85}}$Ga$_{\mathrm{0.15}})$ and observe an extraordinarily large Nernst coefficient at room temperature of 4 $\mu $V/KT. Next we demonstrate a new geometry for efficient and low cost power generation by wrapping Galfenol wire around a hot cylinder. This coil geometry results in a radial temperature gradient direction. With a magnetic field applied in the axial direction, a uniform Nernst electric field is produced along the azimuthal direction at every point along the coil. As a result of this geometry, the Nernst voltage is shown to increase linearly with wire length, proving the concept of scalable Nernst thermal power generation. [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V28.00009: Magnetic microscopy and simulation of strain-mediated control of magnetization in Ni/PMN-PT nanostructures Ian Gilbert, Andres Chavez, Daniel Pierce, John Unguris, Wei-Yang Sun, Cheng-Yen Liang, Gregory Carman We describe high resolution magnetic microscopy of electric-field manipulation of magnetization in multiferroic heterostructures comprised of Ni films and nanostructures deposited on ferroelectric [Pb(Mg$_{\mathrm{1/3}}$Nb$_{\mathrm{2/3}})$O$_{\mathrm{3}}$]$_{\mathrm{0.68}}$[PbTiO$_{\mathrm{3}}$]$_{\mathrm{0.32}}$ (PMN-PT). An applied electric field strains the PMN-PT via the converse piezoelectric effect, changing the magnetic easy axis of the adjacent ferromagnetic layer through magnetostriction. Using scanning electron microscopy with polarization analysis, we image the vector magnetization of the Ni film and submicron disks before and during the application of an electric field. We observe the film's magnetization rotates by 90 degrees upon the application of an electric field. The magnetic vortices present in the Ni disks are compressed into two antiparallel domains oriented along the easy axis defined by the strain. We then use these data to quantitatively demonstrate that a fully coupled micromagnetic-elastodynamic simulation represents the magnetization response to strain more accurately than a simple spatially-uniform uniaxial strain in a standard micromagnetic simulation using only the Landau-Lifshitz-Gilbert equation. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V28.00010: Nanoscale origins of Non-Joulian magnetostriction in Fe-Ga alloys Alexander Gray, Ravini Chandrasena, Weibing Yang, Andreas Scholl, Elke Arenholz, Martin Holt, Jan Minar, Hubert Ebert, Harsh Deep Chopra Recently, a new class of single-crystalline magnets exhibiting a `giant' non-volume-conserving or non-Joulian magnetostriction was discovered [1]. Electronic-structural mechanism giving rise to this unusual phenomenon is not well understood. Here we show the results of our recent investigations of non-Joulian Fe-Ga alloys using high-resolution polarization-dependent photoelectron microscopy (XMCD-PEEM), x-ray absorption spectroscopy (XAS) and hard x-ray nanodiffraction. Strong coupling between the nanoscale modulations in the magnetic and structural properties is observed. The results are compared with the state-of-the-art first-principles theoretical calculations. Combining spectromicroscopic techniques that probe electronic, magnetic and structural degrees of freedom on the nanoscale provides a powerful experimental platform for studying such materials. [1] H. D. Chopra and M. Wuttig, Non-Joulian magnetostriction, Nature 521, 340 (2015). [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V28.00011: Large magnetic anisotropy predicted for metastable structures of rare-earth free Co-Fe-N compounds Xin Zhao, Cai-Zhuang Wang, Liqin Ke, Yongxin Yao, Kai-Ming Ho Metastable structures of cobalt nitrides and Fe-substituted cobalt nitrides are explored as promising candidates for rare-earth free permanent magnets. Through crystal structure searches using adaptive genetic algorithm, new structures of Co$_{\mathrm{n}}$N (n $=$ 3\textellipsis 8) are found to have lower energies than those previously discovered by experiments. Substituting a fraction of Co with Fe helps to stabilize the new structures and at the same time further improve the magnetic properties. Based on first-principles density functional calculation, large magnetic anisotropy energy is predicted in this system, reaching as high as 3.18 MJ/m$^{\mathrm{3}}$ (245.6 $\mu $eV per transition metal atom). In addition, for the extensively studied Fe$_{\mathrm{16}}$N$_{\mathrm{2}}$ magnets, we discuss a tetragonal to cubic structure transition as replacing Fe with Co, which can be well explained by electron counting analysis. Different magnetic properties in Co$_{\mathrm{16-x}}$Fe$_{\mathrm{x}}$N$_{\mathrm{2}}$ between the Co-rich side (x $\le $ 8) and Fe-rich side (x \textgreater 8) is closely related to the structural transition. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V28.00012: Large Magnetic Anisotropy in HfMnP David Parker, Tej Lamichhane, Valentin Taufour, Morgan masters, Srinivasa Thimmaiah, Ser'gey Bud'ko, Paul Canfield We present a theoretical and experimental study of two little-studied manganese phosphide ferromagnets, HfMnP and ZrMnP, with Curie temperatures above room temperature. We find an anisotropy field in HfMnP approaching 10 T - larger than that of the permanent magnet workhorse NdFeB magnets. From theory we determine the source of this anisotropy. Our results show the potential of 3d-element-based magnetic materials for magnetic applications. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V28.00013: Monte Carlo Simulation Study of Atomic Structure of alnico Permanent Magnets Manh Cuong Nguyen, Cai-Zhuang Wang, Kai-Ming Ho Lattice Monte Carlo simulation based on quinternary cluster expansion energy model is used to investigate nano-scale structure of alnico alloy, which is considered as a candidate material for rare-earth free high performance permanent magnets, especially for high or elevated temperature applications such as electric motor for vehicles. We observe phase decomposition of the master alnico alloy into FeCo-rich magnetic ($\alpha $1) and NiAl-rich matrix ($\alpha $2) phases. Concentrations of Fe and Co in $\alpha $1 phase and Ni and Al in $\alpha $2 phase are higher for lower annealing temperature. Ti is residing mostly in the $\alpha $2 phase. The phase boundary between $\alpha $1 and $\alpha $2 phases are quite sharp with only few atomic layers. The $\alpha $1 phase is in B2 ordering with Fe and Al occupying the $\alpha $-site and Ni and Co occupying the $\beta $-site. The $\alpha $2 phase is in L21 ordering with Al occupying the 4a-site. The phase composition profile again annealing temperature suggests that lower annealing temperature would improve the magnetism of $\alpha $2 and diminish the magnetism of $\alpha $2 phase, hence improve shape anisotropy of $\alpha $1 phase rods and that of alnico. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V28.00014: Search for alternative or reduced rare-earth content ferromagnetic materials for permanent magnet applications. Tej Lamichhane, Valentin Taufour, Morgan Masters, Udhara Kaluarachchi, Srinivasa Thimmaiah, Andriy Palasyuk, David Parker, Sergey Bud'ko, Paul Canfield Current commercial magnets (e.g. Nd$_{2}$Fe$_{14}$B and SmCo$_{5}$) are based on critical rare-earth elements like Nd, Dy and Sm and the supply security of these materials is uncertain. Finding new ferromagnetic compounds without critical elements or reducing the content of critical rare-earth elements in existing rare-earth magnets without compromising in magnetic properties are the two possible routes to overcome the problem of criticality. In the first approach, we have synthesized the single crystals of the transition metal rich ternary ferromagnetic compounds: Mn$_{1.05}$Rh$_{0.02}$Bi, solid solution of (Fe$_{1-x}$Co$_{x}$)$_{2}$B, Fe$_{5}$B$_{2}$P, ZrMnP and HfMnP via flux growth technique and studied their magnetic anisotropic properties. In the second option we are exploring the possible routes for reducing the rare-earth content in commercial magnetic materials or finding non-critical rare-earth elements based ferromagnetic materials. In this talk we will review the progress we have made using each of these approaches. [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V28.00015: Magnetic Force Microscopy Study of the Spin Reorientation Transition in Nd$_2$Fe$_{14}$B Muhammad Saleem, Jason Hoffman, Magdalena Huefner, Xiaoyu Liu, Ruslan Prozorov, Paul Canfield, Jennifer Hoffman Nd$_2$Fe$_{14}$B is a hard magnet that possesses one of the highest available magnetic energy density, which has led to its use in many commercial applications, as well as studies of magnetic domain structure. At room temperature, Nd$_2$Fe$_{14}$B shows a strong uniaxial magnetic anisotropy along its crystalline c-axis. At T$_{SR}$ = 135 K it undergoes a spin reorientation transition, below which it shows an easy-cone magnetization where magnetic moments cant away from the c-axis. In this study we use magnetic force microscopy (MFM) to image the magnetic features as a function of temperature through the spin-reorientation transition in Nd$_2$Fe$_{14}$B single crystal. We observe a pronounced change in the anisotropy of the magnetic features upon cooling from 170 K to 100 K. Our analysis reveals an increase in the four-fold component of the anisotropy below T$_{SR}$, which peaks at a length scale around 6 $\mu$m. The magnetic feature size observed here is comparable to previously reported magnetic features of Nd$_2$Fe$_{14}$B using magneto-optical Kerr effect. [Preview Abstract] |
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