2872 IEEE TRANSACTIONS ON MAGNETICS, VOL. 39, NO. 5, SEPTEMBER 2003 Structural and Magnetic Properties of Rhombohedral Sm (Co,Fe,Cr) B and Sm (Co,Fe,Mn) B Compounds Sofoklis S. Makridis, George Litsardakis, Kostas G. Efthimiadis, Eleni Pavlidou, Ioannis Panagiotopoulos, George C. Hadjipanayis, and Dimitris Niarchos Abstract—Single-phase rhombohedral Sm (Co Fe M ) B with M Cr or Mn substituting for Co have been prepared and the influence of transition metals on crystal structure, anisotropy field, and Curie temperature is examined. Sm Co as-cast bulk sample has the 2 : 17 hexagonal structure (type Th Ni ), while boron addition stabilizes the 2 : 17 rhombohedral structure (type Th Zn ). Anisotropy field for Cr-doped as-cast sample is 74 kOe. Secondary phases of fcc-Co or Fe-Co are observed in some cases. A Cr-doped sample with after annealing at 1190 C for 26 h is single phase. Curie temperatures of as-cast samples vary from 849 C to 687 C depending on the composition. Me- chanical alloying and melt spinning were used to develop coercivity. As-spun ribbons at 53 m/s with Cr present a nanocomposite struc- ture with H 5.2 kOe. Samples with Mn have a coercive field close to 0.4 kOe. Scanning electron microscopy studies show dif- ferent microstructure for Mn and Cr substituted ribbon samples. Index Terms—Hard magnetic materials, permanent magnets, rare-earth metals and compounds. I. INTRODUCTION T HE Sm-Co intermetallic phases (2 : 17, 1 : 7, 1 : 5) have anisotropy fields varying from 65 to 300 kOe, respectively. Addition and/or substitution of atoms such as Fe, Mn, Cr, C, B, N for Co modify the magnetic properties—anisotropy, coer- civity, reduced remanence ( / ), energy product , and Curie temperature ( )—making them suitable for perma- nent-magnet applications [1]–[3]. In the present work, we dis- cuss the structural and magnetic properties of Sm Co com- pounds with small boron addition and substitutions of Fe and Manuscript received January 2, 2003. This work was supported by the Euro- pean Commission (EC) HITEMAG project (G5RD-CT2000-00213) and by the EC Human potential program (HPRI-1999-CT-00030). S. S. Makridis is with the Department of Electrical and Computer Engi- neering, Aristotle University, Thessaloniki 54124, Greece and also with the Institute of Materials Science, NCSR “Demokritos,” Athens 15310, Greece (e-mail: sofmak@eng.auth.gr). G. Litsardakis is with the Department of Electrical and Computer Engineering, Aristotle University, Thessaloniki 54124, Greece (e-mail: Lits@eng.auth.gr). K. G. Efthimiadis and E. Pavlidou are with the Department of Physics, Aristotle University, Thessaloniki 54124, Greece (e-mail: kge@auth.gr; pavlidou@rect.auth.gr). G. C. Hadjipanayis is with the Department of Physics and Astronomy, Uni- versity of Delaware, Newark, DE 19716 USA (e-mail: hadji@udel.edu). I. Panagiotopoulos is with the Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece (e-mail: ipanagio@cc.uoi.gr). D. Niarchos is with the Institute of Materials Science, NCSR “Demokritos,” Athens 15310, Greece (e-mail: dniarchos@ims.demokritos.gr). Digital Object Identifier 10.1109/TMAG.2003.815732 Cr or Mn, in the form of arc-melted bulk samples, melt-spun ribbons, and ball-milled powder samples. II. EXPERIMENTAL PROCEDURE Bulk samples of composition Sm (Co Fe M ) B and Sm (Fe Co M ) with M Cr or Mn substituting for Co , , were prepared by repeatable arc melting. From the arc-melted bulk samples, ribbons were produced by melt spinning at 13 to 53 m/s orbital wheel speed. Nanograined powders have been made as well, by means of ball milling in a planetary ball mill, for 16 to 40 h, at 250 r/min speed, with ball to powder mass of 15 : 1. The sam- ples were wrapped with tantalum foil, sealed in quartz tubes under pure argon atmosphere, and then annealed at a tempera- ture range of 900 C–1185 C for 1–60 h. Structural characteris- tics of bulk as-cast and annealed samples have been determined by Rietveld analysis of X-ray diffraction patterns using Fe–K radiation. Isothermal magnetization measurements have been performed in a high field (24 T) extraction magnetometer at the Grenoble High Magnetic Field Laboratory, in order to determine anisotropy field, coercive field, and saturation magnetization of selected samples, while thermomagnetic curves of bulk samples were traced with a vibrating sample magnetometer (VSM) in a field of 300 Oe. Scanning electron microscopy (SEM) studies have been performed using a JEOL JSM-840A instrument. III. RESULTS AND DISCUSSION In the boron-free Sm Co arc-melted bulk sample, the structure is the metastable 2 : 17 hexagonal (space group P6/mmm, type TbCu ). We find out that boron addition stabilizes the 2 : 17 rhombohedral structure (s.g. R m, type Th Zn ; denoted as 2 : 17R) in Sm Co B and in Fe substituted Sm (Co Fe ) B compounds (Fig. 1). Both structures are derivable from the basic rare earth (R)—tran- sition metal (TM) RTM hexagonal structure (s.g. P6/mmm, type CaCu ). Th Ni (2 : 17H) and Th Zn (2 : 17R) derive after a replacement of R by a TM–TM dumbbell in certain sites of R atoms while TbCu derives by random replacement of R atoms by TM–TM dumbbell. In Cr or Mn substituted, boron-free Fe-rich samples Sm (Fe Co Cr ) and Sm (Fe Co Mn ) , the dominant phase is -Fe. These compositions in all cases (as-cast and annealed bulks, as-spun and annealed ribbons at 0018-9464/03$17.00 © 2003 IEEE