Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z14: Permanent Magnet Materials |
Hide Abstracts |
Sponsoring Units: GMAG Chair: George Hadjipanayis, University of Delaware Room: 316 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z14.00001: Magnetic Hardening of Ce$_{2}$Fe$_{\mathrm{14-x}}$Co$_{\mathrm{x}}$B J.F. Herbst, E.J. Skoug, M.S. Meyer, F.E. Pinkerton Permanent magnets based on R$_{2}$Fe$_{14}$B (R $=$ rare earth element) are essential to a wide variety of applications, among them automotive traction motors. Current state-of-the-art materials rely on R $=$ Nd and Dy, both of which are currently subject to supply and cost instability. A possible alternative is R $=$ Ce, the most abundant rare earth, but Ce$_{2}$Fe$_{14}$B has several disadvantages, including a low Curie temperature (T$_{\mathrm{c}})$ that restricts the maximum operating point to well below that required for some applications. Given that substitution of Co for Fe is known to enhance T$_{\mathrm{c}}$ significantly in other R$_{2}$Fe$_{14}$B compounds, we systematically investigate magnetic hardening of Ce$_{2}$Fe$_{\mathrm{14-x}}$Co$_{\mathrm{x}}$B by melt spinning alloys having compositions guided by our previous work on the Ce-Fe-B system. We find the range of Co solubility in Ce$_{2}$Fe$_{14}$B to be markedly lower than for other R$_{2}$Fe$_{14}$B materials, a consequence of the fact that Ce$_{2}$Co$_{14}$B apparently does not form. [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z14.00002: Mechanochemical synthesis of (Sm,Pr)$_2$(Co,Fe)$_{17}$ powders for nanocomposite permanent magnets George Hadjipanayis, Alexander Gabay, Wanfeng Li Bottom-up fabrication of nanocomposite permanent magnets with enhanced maximum energy product requires large quantities of high-coercivity powder with crystallographically anisotropic particles tens of nanometers in size. In this work, we report a systematic study aimed to employ combination of intensive mechanical milling and calciothermic reduction for preparation of polydispersed (Sm,Pr)$_2$(Co,Fe)$_{17}$ powders with a predominant-to-significant part of the particles smaller than 100 nm. In addition to the effects of Pr and Fe on the hard magnetic properties of the particles, the study analyzes the influence of excess reducing agent Ca and that of the heat treatment on the particle size distribution, their chemical/structural homogeneity and crystallographic anisotropy. Emphasized is the likely role of the excess Ca facilitating the diffusion-enabled particle growth. Remanent magnetization up to 106 emu/g and intrinsic coercivity up to 14 kOe were obtained. [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z14.00003: High Coercivity Anisotropic Nd2Fe14B Nanoparticles Produced by Planetary Ball Milling Ozlem Koylu-Alkan, George C. Hadjipanayis, Dimitris Niarchos The bottom-up fabrication of anisotropic exchange-coupled nanocomposites brings out the necessity of fabrication of magnetically hard nanoparticles with high coercivity. In this study, we have fabricated Nd$_{2}$Fe$_{14}$B nanoparticles from die-upset Nd-Fe-B (MQ3) precursor materials using planetary milling. The MQ3 alloy consists of platelets which are approximately 80 nm in thickness and 500 nm in diameter. Using planetary ball milling we were able to produce Nd$_{2}$Fe$_{14}$B nanoparticles with a size down to 20 nm. However, the size distribution of the milled particles is very broad ranging between 20 nm and 20 $\mu m$. A sedimentation experiment was used to separate the different size particles. By allowing bigger particles to sediment in a viscous liquid, we were able to separate different size nanoparticles with a size smaller than 200 nm. The coercivity of particles is found to decrease with particle size. After 60 min sedimentation the collected particles had an average size 100 nm with a coercivity value of 5.4 kOe. The objective of this study is to obtain nanoparticles with a size below 100 nm and a coercivity greater than 10 kOe for the fabrication of anisotropic exchange-coupled nanocomposites. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z14.00004: Synthesis of CeFe$_{10.5}$Mo$_{1.5}$ with ThMn$_{12}$-Type Structure by Melt Spinning Chen Zhou, Misle Tessema, Martin Meyer, Frederick Pinkerton Rare earth compounds RFe$_{12-x}$M$_{x}$ with tetragonal ThMn$_{12}$-type structure are of great interest for potential applications as permanent magnets. These materials serve as precursors for nitriding and hydriding, processes which can dramatically increase the Curie temperature, spontaneous magnetization, and affect the magnetic anisotropy. We report the phase study of CeFe$_{10.5}$Mo$_{1.5}$ samples melt spun at various surface wheel speeds v$_{s}$ between 5 and 60 m/s. The results from quantitative Rietveld analysis indicate that the as-spun ribbons are a mixture of primary CeFe$_{10.5}$Mo$_{1.5\, }$phase with impurity phases such as Ce$_{2}$Fe$_{17}$, Fe-Mo compound and CeFe$_{2}$. At wheel speeds v$_{s}$ below 25 m/s, CeFe$_{10.5}$Mo$_{1.5\, }$phase accounts for greater than 85 wt{\%}, while the Fe-Mo compound is the only detectable impurity phase. Above v$_{s\, }=$ 25 m/s, as the wheel speed increases, CeFe$_{10.5}$Mo$_{1.5\, }$phase decreases monotonically to about 60 wt{\%} at v$_{s\, }=$ 60 m/s while the amounts of impurity phases increase. Thermogravimetric measurement indicates that the Curie temperature T$_{c}$ of the CeFe$_{10.5}$Mo$_{1.5\, }$phase is 340 K. As a result, the best performing sample melt spun at v$_{s}=$15m/s only exhibits an energy product BH$_{max}=$0.121 MGOe at room temperature. Although such a number is modest for a permanent magnet, nitriding is expected to greatly enhance the Curie temperature, and hence the magnetic performance. [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z14.00005: Giant magnetic anisotropy in Li$_{3-x}$Fe$_x$N permanent magnets Anton Jesche, Srinivasa Thimmaiah, Sergey Bud'ko, Paul Canfield Single crystals of Li$_2$(Li$_{1-x}$Fe$_x$)N were successfully grown out of Li-flux. Fe-concentrations and lattice parameters were determined by means of single crystal and powder diffraction which also confirmed the substitution of Fe on only one of the Li sites resulting in Li$_{1-x}$Fe$_x$ layers separated by Li$_2$N layers. Magnetization measurements revealed a ferromagnetically ordered ground state with Curie temperatures of $\sim 60$\,K for Fe concentrations of $x \approx 20$\%. Large saturation moments of up to 5\,$\mu_B$ per Fe atom were found along the hexagonal crystallographic $c$-axis. These values exceed the spin-only contribution of Fe and are also reflected in correspondingly large effective moments at room temperature. The anisotropy field at $T = 2$\,K, defined as intersection of the magnetization for $M \parallel c$ and $M \perp c$, can be estimated to lie well beyond 100 Tesla. Electrical resistivity measurements show insulating behavior and raise questions about the nature of the underlying magnetic exchange mechanism. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z14.00006: Combinatorial search of rare-earth free permanent magnets Tieren Gao, Ichiro Takeuchi, Sean Fackler, Lei Fang, Ying Zhang, Matthew Krammer, Iver Anderson, Bill McCallum Permanent magnets play important roles in modern technologies such as in generators, motors, speakers, and relays. Today's high performance permanent magnets contain at least one rare earth element such as Nd, Sm, Pr and Dy. However, rare earth elements are increasingly rare and expensive, and alternative permanent magnet materials which do not contain them are needed by the industry. We are using the thin film composition spread technique to explore novel compositions of permanent magnets without rare-earth. Ternary co-sputtering is used to generate composition spreads. We have thus far looked at Mo doped Fe-Co as one of the initial systems to search for possible compounds with enhanced coercive fields. The films were deposited on Si (100) substrates and annealed at different temperatures. The structural properties of films are mapped by synchrotron diffraction. We find that there is a structural transition from a crystalline to an amorphous state at about 20{\%} atomic Mo. With increasing annealing temperature, the Mo onset concentration of the structural transition increases from 25{\%} for 600$^{\circ}$C to 35{\%} for 700$^{\circ}$C. We find that some of compounds display enhanced coercive field. With increasing Mo concentration, the magnetization of Fe-Co-Mo begins to switch from in-plane to out-of-plane direction. This work is funded by the BREM (Beyond Rare-earth Magnet) project (DOE EERE). [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z14.00007: Electronic structure and equation of state of Sm$_2$Co$_{17}$ from first-principles DFT+$U$ Patrick Huang, Nicholas P. Butch, Jason R. Jeffries, Scott K. McCall Rare-earth intermetallics have important applications as permanent magnet materials, and the rational optimization of their properties would benefit greatly from guidance from ab initio modeling. However, these systems are particularly challenging for current electronic structure methods. Here, we present an ab initio study of the prototype material Sm$_2$Co$_{17}$ and related compounds, using density functional theory with a Hubbard correction for the Sm 4$f$-electrons (DFT+$U$ method) and ultrasoft pseudopotentials. The Hubbard $U$ parameter is derived from first principles [Cococcioni and de Gironcoli, PRB 71, 035105 (2005)], not fit to experiment. Our calculations are in good agreement with recent photoemission measurements at ambient pressure and the equation of state up to 40 GPa, thus supporting the validity of our DFT+$U$ model. [Preview Abstract] |
Friday, March 22, 2013 12:39PM - 12:51PM |
Z14.00008: Effects of pressure on the sturctural and magnetic properties on Sm based permanent magnets Scott McCall, Nicholas Butch, Jason Jeffries, Patrick Huang The magnetic properties of the rare earth-transition metal permanent magnets are sensitive to interatomic spacing and can be tuned by adjusting these parameters. We report the effects of high pressure on the crystal structure and magnetic properties of Sm$_{2}$Co$_{17}$ and Sm$_{2}$Fe$_{17}$ measured in diamond anvil cells. [Preview Abstract] |
Friday, March 22, 2013 12:51PM - 1:03PM |
Z14.00009: Site-preference and valency for rare-earth sites in (R-Ce)2Fe14B [R$=$La,Nd] magnets Aftab Alam, Mahmud Khan, R.W. McCallum, D.D. Johnson Rare-earth (R) permanent magnets of R2Fe14B have technological importance due to their high energy products, and they have two symmetry distinct R-sites (Wyckoff 4f and 4g) that affect chemistry and valence. Designing magnetic behavior and stability via alloying is technologically relevant to reduce critical (expensive) R-content while retaining key properties; cerium, an abundant (cheap) R-element, offers this potential. We calculate magnetic properties and Ce site preference in (R{1-x}Ce$_{x}$)Fe14B [R=La,Nd] using density functional theory (DFT) methods. The Fe moments compare well with neutron scattering data -- remain weakly affected by Hubbard U, but improved with spin-orbit coupling. In (La,Ce)2Fe14B, Ce alloys for 0 $<$ x $<$ 1 with a preference for smaller R(4f) sites, as observed, a trend we find unaffected by valence. Whereas in (Nd,Ce)2Fe14B, Ce is predicted to have limited alloying (x $<$ 0.3) with a preference for larger R(4g) sites, resulting in weak partial ordering and segregation. Curie temperatures versus $x$ were predicted for a typical sample processing and verified experimentally. We shall also present some initial results on the critical mixed valency of Ce in related compounds. [Preview Abstract] |
Friday, March 22, 2013 1:03PM - 1:15PM |
Z14.00010: Nucleation-Mode Localization in Hard-Soft Nanocomposites Ralph Skomski, Balamurugan Balasubramanian, Bhaskar Das, D. J. Sellmyer Aligned hard-soft nanocomposites continue to be an active research area in permanent magnetism, challenged by demanding processing requirements but also encouraged by experimental proofs of principle. The approach was initially outlined by Kneller and Hawig (1991), who advocated hard-soft multilayers. Skomski and Coey (1993) considered three-dimensional nanostructures, such as soft spheres in a hard matrix, and predicted an upper energy-product limit of about 1000 kJ/m$^{\mathrm{3}}$. It is well-established that the dimensions of the soft regions cannot be larger than twice the domain-wall width of the hard phase, but otherwise it was believed that geometry has a rather secondary effect. However, our recent research reveals substantial differences. Soft-in-hard geometries are better than hard-in-soft geometries and embedded soft spheres are better than multilayers. This is in close analogy to the dimensionality-dependent quantum-mechanical delocalization of electrons in an inhomogeneous potential and to the behavior of impurity states in the band gaps of solids. Transparent analytical nucleation-field solutions are found for some geometries and in the limit of very small soft inclusion as a function of the hard-phase coercivity and hysteresis-loop shape. [Preview Abstract] |
Friday, March 22, 2013 1:15PM - 1:27PM |
Z14.00011: Frequency dependence of Verdet constant of Bismuth-Doped Rare-Earth Iron Garnets for Magneto-Optic Sensor Applications Mannix Shinn, Rongjia Tao, Dong Ho Wu, Anthony Garzarella There is growing interest in applying magneto-optic materials toward sensor applications. One of these applications is to exploit the Faraday Effect to measure magnetic fields. Bismuth-doped rare-earth iron garnets have proven to be highly sensitive Faraday rotators, but their frequency response and dynamic range to magnetic fields require further study. The Faraday Effect was studied in two samples of bismuth-doped rare-earth iron garnets grown in different conditions, and experiments were performed in a static field as well as in a RF field. Static magnetic fields up to 3 kG were used, and we found that the Faraday rotation became saturated at high fields, indicating that the field dependence follows the hyperbolic tangent function. We extracted each sample's Verdet constant from the Faraday rotation at low magnetic fields of \textless\ 0.1 kG. These experiments were repeated using different laser probe beam wavelengths, ranging from 405 nm to 2000 nm. We measured the transmission coefficient and the Verdet constant for each sample for different probe beam wavelengths and for an external magnetic field at various frequencies. We will discuss the implication of our experimental results. [Preview Abstract] |
Friday, March 22, 2013 1:27PM - 1:39PM |
Z14.00012: Magnetism in Mo-doped Yttrium Iron Garnet S. Khanra, Y. Kolekar, M. Langhoff, P. Kahol, K. Ghosh Yttrium iron garnet (YIG) is a synthetic garnet and ferrimagnetic, with chemical formula Y$_{3}$Fe$_{5}$O$_{12}$. In YIG, five iron (III) ions occupy two octahedral and three tetrahedral sites, with the yttrium (III) ions coordinated by eight oxygen ions in an irregular cube. The iron ions in the two coordination sites exhibit different spins, resulting in magnetic behavior. Bulk YIG has been synthesized systematically by solid state reaction method. The formation of pure YIG have been investigated through X-ray diffraction (XRD) beginning from weighing in molar proportions of Y$_{2}$O$_{3}$ and Fe$_{2}$O$_{3}$, mixing and grinding, pre-sintering and final sintering at 1300 $^{\circ}$C. XRD study shows that YIG exhibits cubic structure with lattice constant of about 12 {\AA}. Magnetization with varying field and temperature has been measured using a SQUID magnetometer. Magnetic measurement of Mo YIG has shown that magnetic moment increase initially and then decreases with Mo doping. Detailed results will be discussed in this presentation. This work is supported by National Science Foundation (Award Number DMR-0907037). [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 1:51PM |
Z14.00013: Local imaging of the phase transition in single crystal Nd$_2$Fe$_{14}$B Magdalena Huefner, Adam Pivonka, Cun Ye, Martin Blood-Forsythe, Ruslan Prozorov, Paul Canfield, Jennifer Hoffman The magnetic microstructure of hard magnets is of interest for immediate industrial applications and for fundamental understanding of the relationship between microscopic and macroscopic magnetic properties in materials. Of particular interest is Nd$_2$Fe$_{14}$B, which shows strong anisotropy with an easy axis along the c-axis at room temperature, but undergoes a phase transition around T$\sim$135K to an easy cone magnetization where the magnetic moments are canted away from the c-axis. Here we present magneto-optical Kerr effect (MOKE) and magnetic force microscope (MFM) measurements to investigate the spin-reorientation phase transition in single crystal Nd$_2$Fe$_{14}$B. The MFM measurements resolve a continuous change in the domain structure from rounded flower-shaped domains of a lateral extent $\sim$200 nm-$\sim$7$\mu$m to larger rectangular features of typical width $\sim$1$\mu$m and length $\sim$10$\mu$m-$\sim$30$\mu$m. By imaging the same surface area in small temperature steps across the phase transition we track the evolution of single features. [Preview Abstract] |
Friday, March 22, 2013 1:51PM - 2:03PM |
Z14.00014: Magnetization and scanning tunneling spectroscopy studies of Mn$_{1.5}$Ga films on GaAs(001) Jaesuk Kwon, Xin Zhang, John Hatch, Archana Kumari, Hui Xing, Payam Taherirostami, Hao Zeng, Jeffrey Cogswell, Joseph A. Gardella, Hong Luo Hard magnetic materials have applications in permanent magnets and data storage media. Free of rare earth elements, L1$_{0}$ structured Mn$_{1.5}$Ga with high magnetic anisotropy is a potential candidate for such applications. Epitaxial films of Mn$_{1.5}$Ga with different thicknesses (35 nm -- 200 nm) were grown on GaAs(001) by molecular beam epitaxy. Films with thicknesses of 35 nm and 50 nm present uniform surface morphology which consists of overlapping rectangular features with widths and lengths on the order of a few tens to a few hundred nanometers. Measurements of X-ray diffraction reveal the presence of an interfacial layer of Mn$_{2}$As between the substrate and L1$_{0}$ Mn$_{1.5}$Ga. The 200 nm thick film presents a mixture of two different surface structures: domains which consist of faceted tent-like structures and domains with flat terraces (with lateral dimensions of about 500 nm). The magnetic properties of all samples are studied by vibrating sample magnetometer and their correlation with their surface morphology and stoichiometry will be presented. Scanning tunneling spectroscopy measurements of the 200 nm thick Mn$_{1.5}$Ga film reveal electrical inhomogeneity correlated to the two morphologies. This work was supported by NSF DMR1006286. [Preview Abstract] |
Friday, March 22, 2013 2:03PM - 2:15PM |
Z14.00015: Magnetic anisotropy of strained MnGa alloys Renat Sabirianov, Nabil Al-Aqtash MnGa is a promising candidate for Rare Earth free permanent magnet applications because it has a large magnetocrystalline anisotropy. We examine the variation of the magnetocrystalline anisotropy of these alloys as function of bi-axial in-plane strain using ab-initio electronic structure calculations. We employed force theorem to calculate the MAE$=$E(\textbar \textbar )-E($\bot )$ as difference of energies of the system with magnetization along and perpendicular to the easy axis. Using projector augmented wave method implemented in VASP we have calculated MAE in MnGa, Mn$_{3}$Ga and Mn$_{\mathrm{1+x}}$Ga$_{\mathrm{1-x}}$ alloys. We find that the MAE is 2.5MJ/m$^{3}$ (0.42meV/u.c.) and 0.12MJ/m$^{3}$ (0.07meV/u.c.) in unstrained MnGa and Mn$_{3}$Ga, respectively. MAE decreases if bi-axial strain is applied in MnGa. Thus, the anisotropy of this system can be affected by the strain. We also discuss the effect of Mn disorder on MAE in Mn$_{\mathrm{1+x}}$Ga$_{\mathrm{1-x}}$ alloys. [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