Materials Science for High-Performance Permanent Magnets: Search for New Hard Magnets / Non-Rare Earth Magnets
Sponsored by: TMS Functional Materials Division, TMS: Magnetic Materials Committee
Program Organizers: Satoshi Hirosawa, National Institute for Material Science; Matthew Kramer, Iowa State University; Oliver Gutfleisch, Technische Universität Darmstadt; Hae-Woong Kwon, Pukyong National University

Thursday 8:30 AM
March 2, 2017
Room: 24C
Location: San Diego Convention Ctr

Funding support provided by: Elements Strategy Initiative Center for Magnetic Materials

Session Chair: Christian Elsässer, Fraunhofer-Institut für Werkstoffmechanik

8:30 AM  Invited
Search for Substitutes of Magnetic Materials Containing Critical Elements by High-throughput Screening and Multi-scale Modeling Approaches: Christian Elsaesser1; Wolfgang Körner1; Georg Krugel1; Daniel Urban1; 1Fraunhofer IWM Freiburg
    This lecture discusses possibilities to discover new magnetic phases, by employing computational high-throughput-screening (HTS) and multi-scale-modeling approaches, to substitute known magnets like Nd2Fe14B, which have outstanding functionalities but also constraining criticalities. To discover promising magnetic phases, a HTS approach based on density functional theory (DFT) is employed to search for structures and compositions of intermetallic phases of transition-metal and rare-earth (RE) elements, which have good intrinsic ferromagnetic properties but contain less amounts of critical RE elements than Nd2Fe14B. The development of permanent magnets from magnetic phases requires multi-scale modeling to take into account how microstructure influences magnetic behavior. The scaling-up in size of atomistic models can be achieved by employing efficient tight-binding total-energy models and bond-order potentials derived from DFT. Further scaling-up to multi-domains and poly-crystals can be done by phenomenological micro-magnetic or phase-field models parameterized using DFT data. The lecture closes with an outlook towards this direction.

8:55 AM  Invited
Towards High-performance Permanent Magnets without Rare Earths: Konstantin Skokov1; 1Technische Universität Darmstadt
    The pressing need to reduce the consumption of rare earths in the permanent-magnet industry has rekindled the interest in 3d ferromagnets. The main obstacle in the way of a 3d-only high-performance permanent magnet is insufficient anisotropy (and hence, coercivity). Achieving a very strong magnetic anisotropy in a 3d material without rare earths elements is a difficult, but not an impossible task. Several strategies can be pursued in this situation and some of them will be discussed in this talk. In this work, LaCo5, YCo5, (FeCo)2B, MnAlGe, MnBi, Fe3Sn and Fe2Ge single crystals were grown. Analysis of magnetization curves along the hard axis was performed and temperature dependences of anisotropy constants K1 and K2 were found. MnAl, MnBi, MnAlGe etc. permanent magnets have been prepared and their extrinsic magnetic properties (Hc, Br) will be compared with intrinsic properties of material (K1, Ms).</P>

9:20 AM  Invited
Bulk High-throughput Experimentation to Discover New Hard Magnets: Dagmar Goll1; Gerhard Schneider1; 1Aalen University
    Novel magnet materials filling the gap between hard ferrites and Fe-Nd-B are desirable for efficient energy converters. Finding interesting candidates within the huge number of so far unexplored multicomponent systems requires an elaborate concept for efficient screening. Our bulk high-throughput approaches are well-suited to scan rapidly through multicomponent systems. Core of the approach are diffusion couples. These heterogeneous non-equilibrium states allow coverage of the most relevant part of a so far unexplored phase diagram by one single sample. Identification of the magnetic phases and analysis of the corresponding intrinsic magnetic properties is performed by combining different microscopy techniques. From domain size and domain contrast the intrinsic material parameters (saturation magnetization, magnetic anisotropy, Curie temperature) can be deduced. Besides introducing the principles and latest developments of the methodology for its successful application novel hard magnets (e.g. RE-lean/Ce-based, RE-free) and their properties will be presented and discussed within the framework of micromagnetism.

9:45 AM  
Search for New Rare-earth-free Hard Magnetic Materials Using Solution Growth: Valentin Taufour1; Tej Lamichhane2; Michael Onysczcak2; Olena Palasyuk2; David Parker3; Sergey Bud'ko2; Paul Canfield2; 1University of California-Davis, Critical Material Institute; 2Ames Laboratory, Critical Material Institute; 3Oak Ridge National Laboratory, Critical Material Institute
    One of the key ingredients to the properties of permanent magnets is the large uniaxial magneto-crystalline anisotropy which usually arises from rare-earth elements such as neodymium or dysprosium. Their cost, limited availability and environmental impact has motivated the scientific community to look for new magnetic compounds with less rare-earth. The challenge is to obtain large magneto-crystalline anisotropy with non-rare-earth elements. We studied the magnetic anisotropy of single crystals of new materials grown using the solution growth technique. We found large magnetic anisotropy in several Mn, Fe and Co based ferromagnets and discuss their suitability for permanent magnet applications. We discovered new ferromagnets such as HfMnP and ZrMnP which have large anisotropy, we study the change from planar to axial anisotropy with temperature and substitutions in Fe2B alloys and we report on axial anisotropy in Fe5B2P.

10:05 AM Break

10:20 AM  
L10-FeNi Films with Coercivity in Excess of 1 kOe: A Combinatorial Sputtering Approach: Georgios Giannopoulos1; Andreas Kaidatzis1; Gaspare Varvaro2; Ruslan Salikhov3; Vasilis Psycharis1; Sara Laureti2; Alberto Maria Testa2; Michael Farle3; Dimitris Niarchos1; Margaritis Gjiokas1; 1NCSR Demokritos; 2ISM-CNR; 3Faculty of Physics and Center for Nanointegration (CENIDE)
     L10-type magnetic compounds, including FeNi, possess promising technical magnetic properties of both high magnetization and large magnetocrystalline anisotropy energy and thus offer potential in replacing rare earth permanent magnets in many applications. In this work, we have employed a combinatorial sputtering process [1] in order to study the conditions of fabricating the L10-FeNi phase. We have used Si(100) wafers as substrates and we deposit FeNi on a variable stoichiometry Cu-Au-Ni buffer to match the lattice constants of the L10-FeNi. We perform magnetic properties and we find that the coercivity increases from approximately 0.3 kOe to 1 kOe as the Au content of the combinatorial interlayer decreases, without any further annealing optimization. A thorough structural and magnetic properties study will be presented. ACKNOWLEDGEMENTS - Funding from the E.C. is acknowledged (Grant No. 318144, 280670, 686056-NOVAMAG and 691235-INAPEM). REFERENCES: [1] X.-D. Xiang, X.-D Sun et al, Science (1995) p. 1738

10:40 AM  
Structure and Magnetic Properties of Fe3Sn1-xMx (M=Sb, P): Margarit Gjoka1; Vasilis Psycharis1; Charalambos Sarafidis2; Eamonn Devlin1; Dimitris Niarchos1; 1NCSR Demokritos; 2Department of Physiscs, Aristotle University of Thessaloniki
    The magnetic properties of hexagonal Fe3Sn make it a promising phase for a new permanent magnet. Unfortunately the easy magnetic axis of this alloy lies in the hexagonal plane. Theoretical calculations to identify a possible substitutional alloy based on Fe3Sn, with uniaxial anisotropy, are reported by B. C. Sales et al [1]. In this work the synthesis and investigation of alloys with nominal composition Fe3Sn1-xMx (M=Sb, P, x=0-0.25) are reported. The samples are produced by arc melting and mechanical alloying, and then annealed in the interval 800-1000 oC. The alloys exhibit various magnetic phases, the majority being Fe3Sn with extra phases of the type Fe5Sn3, α-Fe(Sn) and Fe3Sn2. The magnetic and structure characterisation of the samples with different heat treatments will be presented. [1] B.C. Sales, B. Saparov, M.A. McGuire, D.J. Singh, D.S. Parker, Scientific Report, 2014, DOI: 10.1038/srep07024. Supported by the EU project INAPEM.

11:00 AM  
Magnetic Anisotropy of Epitaxially Grown L10 Mn-(Ga,Al) Alloy Thin Films: Takao Suzuki1; Siqian Zhao1; 1University of Alabama
    The L10 MnAl and MnGa are known to exhibit the high magnetic anisotropy constant K of 107erg/cc at room temperature. A recent experimental work suggested that the K(T) for L10 MnAl nano-crystalline thin films linearly decreases with saturation magnetization Ms(T).1 On the other hand, the K for the L10 MnGa nano-crystalline thin films exhibited the 8th power dependence on Ms(T).2 Those experimental results are at variance with a single ion model where one would expect the major contribution of Mn to the magnetic anisotropy, thus expect the 3rd or higher power dependence. Epitaxially grown thin films of L10 MnGa have been successfully fabricated onto MgO(100) single crystal substrates by sputter-deposition. The magnetic anisotropy constant K measured by a torque method over a temperature range from 5 to 400K is discussed in conjunction with the temperature change of Ms. The work was partially supported by NSF-CMMI 1229049. References: 1.S. Zhao,et al.: IEEE Trans.MAG.51, 2101604(2015); 2.S. Zhao,et al.: AIP Advances,6,056025(2016).

11:20 AM  
Microstructural Characterization of Magnetic MnAl Alloys: Merve Genc1; Ozgun Acar1; Ilkay Kalay2; Eren Kalay1; 1METU; 2Cankaya University
    Rare-earth free Mn-Al permanent magnet alloys exhibit an attractive combination of magnetic properties for several technological applications. Its magnetism arises from a metastable tetragonal tau-phase originated from a hexagonal close-packed epsilon-phase. Even though there are many theories postulated on the transformation mechanism from epsilon-to-tau phase, the answer is still unclear. At a given composition one can favor one mode over the other by choosing the appropriate composition and annealing temperature. It was observed that transformation sequence and the corresponding magnetic properties has been profoundly affected by the existence of an intermediate ε prime phase. We found that epsilon prime can be retained upon quenching for a narrow range of composition which yields to direct formation of ferromagnetic tau. The predominant phase transformation mode of ferromagnetic tau from retained epsilon prime phase will be discussed in details based on in-situ, conventional and high-resolution TEM analyses.

11:40 AM  
Magnetic Anistropy and Microstructure Interplay in Fe16N2 Based Permanent Magnets: Md Mehedi1; Yanfeng Jiang1; Jian-Ping Wang1; 1University of Minnesota
    Rare-earths are expensive, the extraction process is energy intensive and hazardous for the environment and human health. Fe16N2 is regarded as one of the potential candidates of rare-earth-free, permanent magnets for its high magnetocrytalline anisotropy and high saturation magnetization.The coercivity of a magnet is an extrinsic property of a material, which depends largely on the microstructure.We will present both theoretical calculation and experimental results of microstructure-coercivity relation in Fe16N2. The first principal calculation was done using analytical equations relating coercivity and microstructure. The maximum coercivity from a pure Fe16N2 magnet will be close to 9000 Oe, which can produce a permanent magnet of energy product over 100 MGOe. We will also demonstrate the effect of doping on the magnetic microstructure by using images from scanning electron microscope. The interplay of grain boundary engineering and magnetic behavior will also be demonstrated in the presentation.