2922 IEEE TRANSACTIONS ON MAGNETICS, VOL. 38, NO. 5, SEPTEMBER 2002 High Coercivity in Boron Substituted Sm–Co Melt-Spun Magnets Sofoklis S. Makridis, George Litsardakis, Ioannis Panagiotopoulos, Dimitrios Niarchos, Yong Zhang, and George C. Hadjipanayis Abstract—The structural and magnetic properties of nanocom- posite melt-spun Sm Co Fe Cu Zr B magnets have been investigated as a function of boron content , wheel speed and annealing conditions. The as-spun ribbons are nanocrystalline with fine microstructure and average grain size of 60–100 nm. X-ray diffraction indi- cates that the as-spun samples have the metastable hexagonal TbCu -type structure phase and fcc-Co as a secondary soft phase. Magnetization at nonsaturating 5 T field is 45–72 emu/g and the reduced remanence is above 0.8. The loop shape exhibits a characteristic step due to the soft magnetic phase. At room temperature, values of 20–28 kOe are obtained for as spun samples, with a record value of 38.5 kOe for . At 380 C , values higher than 5 kOe are observed. Coercivity and loop shape are strongly dependent on annealing conditions. Index Terms—Hard magnetic materials, permanent magnets, rare earth metals and compounds. I. INTRODUCTION T HE Sm Co -based magnets are known for their large en- ergy product and high operational temperature. A series of recent studies has focused on the composition ad- justment of Sm Co,Fe,Cu,Zr – magnets to optimize them for high-temperature applications [1]–[3]. In these magnets, the desired magnetic properties are obtained after a long and com- plicated heat treatment which is required to develop the proper microstructure with the well-known cellular/lamellar features [4]. The microstructure consists of Th Zn (R-3m) type struc- ture cells rich in Fe, cell boundaries of CaCu (P6/mmm) type structure rich in Cu and the Zr-rich “Z-phase” lamellae, super- imposed on the cellular structure perpendicularly to the hexag- onal axis [5]. The coercivity is generally attributed to a pin- ning type mechanism. Due to the difference in the magnetocrys- talline anisotropy and the domain wall energy of the 2:17 and 1:5 phases, the domain walls are pinned at the 1:5 phase cell boundaries. Manuscript received February 13, 2002; revised May 27, 2002. This work was supported in part by DARPA Metamaterial Program (USA) and by the EC project HITEMAG project (G5RD-CT2000-00213). S. S. Makridis and G. Litsardakis are with the Department of Electrical and Computer Engineering, Aristotle University, Thessaloniki GR-54124, Greece (e-mail: sofmak@eng.auth.gr; Lits@eng.auth.gr) I. Panagiotopoulos and D. Niarchos are with the Institute of Materials Science, NCSR Demokritos, Athens GR-15310, Greece (e-mail: panagiot@ ims.demokritos.gr; niarchos@ims.demokritos.gr). Y. Zhang and G. C. Hadjipanayis are with the Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 USA (e-mail: yzhang@physics.udel.edu; hadji@udel.edu). Digital Object Identifier 10.1109/TMAG.2002.803068. Recently, we have prepared by melt spinning boron sub- stituted Sm Co,Fe,Cu,Zr nanocomposite materials which present high coercivity values associated with a different type of microstructure [6]. A homogeneous nanoscale microstruc- ture accounts for the high coercivity and is obtained in as-spun ribbons or after short annealing. The simple heat treatment is very attractive for developing high-performance magnet materials by a more economical process. Previous attempts to obtain 2:17-based nanocomposite materials by melt-spinning, with and without B or C additives, resulted in rather low values [7]–[10]. In this work, we extend the study of the structural and magnetic properties of nanocomposite melt-spun Sm Co Fe Cu Zr B magnets to higher B substitution range ( , 0.010, 0.015, 0.025, 0.03, 0.04, 0.05) and report very high values. II. EXPERIMENT All bulk-alloys samples were prepared by arc-melting under argon atmosphere. To compensate for the Sm losses during processing an excess of 5%–10%, Sm was added to all samples. Ribbons have been obtained from master alloys by melt-spin- ning using a quartz tube with an orifice diameter of about 0.5 mm, about 2 atm pressure of 99.999 pure argon and a wheel speed of 10–70 m/s. The ribbons were wrapped with tantalum foil and sealed in a quartz tube under argon atmosphere to avoid oxidization and then annealed at temperatures from 750 C up to 900 C for short time (5–15 min). The phases in bulk and ribbon samples were determined by X-ray diffraction (XRD) using FeK radiation. Magnetic properties of the samples were measured by vibrating sample magnetometers (VSM) with maximum field of 5 and 9 T. High-temperature measurements have been performed by a VSM with a maximum field of 2 T. Thermomagnetic curves for the determination of Curie temperature have been traced up to 900 C in a field of 0.05 T. The crystallization behavior has been monitored with differential thermal analysis (DTA) while SEM/EDAX with microprobe analysis was used to examine the stoichiometry of the samples. The microstructure was determined through electron microscopy using a Jeol JEM 2000FX microscope. III. RESULTS AND DISCUSSION The as-spun ribbons are not amorphous irrespective of the B content and wheel speed. Typical X-ray powder patterns of the as-spun ribbons for different B content are shown in Fig. 1. They 0018-9464/02$17.00 © 2002 IEEE