Journal of Alloys and Compounds 369 (2004) 152–154 Enhanced magnetic properties in Zr-containing rare earth-rich Didymium (Nd/Pr)-based nanocrystalline hard magnetic alloys I. Betancourt a,∗ , H.A. Davies b a Materials Research Institute, UNAM, P.O. Box 70-360, Mexico, DF 04510, Mexico b Department of Engineering Materials, University of Sheffield, Sheffield S13JD, UK Abstract A systematic study of the influence of processing conditions and Zr addition on the magnetic properties of RE-rich, Didymium (Nd/Pr) 14 Fe 80 - B 6 (Nd:Pr ratio of 3:1) is reported. For directly quenched alloys, various roll speeds resulted in grain sizes d g within the range 35–50 nm. Increasing remanence J r and maximum energy product (BH) max values were observed as d g decreased (up to 0.86 T and up to 124 kJ/m 3 , respectively). Small Zr addition (1 at.%) resulted in improved J r and (BH) max (up to 0.92 T and up to 142 kJ/m 3 , respectively). For overquenched and annealed alloys, partial substitution of Fe by Zr (0–4 at.%) indicated a marked dependence of the magnetic properties on Zr content, with an excellent combination of J r , (1.0 T), i H c (1574 kA/m) and (BH) max (149 kJ/m 3 ) at 2 at.% Zr. Results are interpreted in terms of variations in the scale of the nanostructure and of the effects of Zr substitutions into the 2/14/1 unit cell. © 2003 Published by Elsevier B.V. Keywords: Permanent magnets; Magnetic measurements 1. Introduction The processing windows for obtaining optimum nanos- tructures and magnetic properties by direct quenching via melt spinning to ribbons in NdFeB-based alloys tend to be narrow and the properties within large batches are likely to be rather variable [1]. An alternative process route is to overquench to a fully amorphous state, followed by a controlled devitrification anneal to a nanoscale grain struc- ture. This has been shown, in some cases, to yield mag- netic properties comparable with those attainable by direct quenching [2]. Also, the substitution of Nd by Pr in nanos- tructured RE 2 Fe 14 B hard magnetic alloys is of interest be- cause the anisotropy field H A and the intrinsic coercivity i H c , are increased [3]. For RE-rich compositions (y> 12 in RE y Fe 94-y B 6 alloy systems) having already large i H c val- ues (typically above 1000 kA/m) this substitution is expected to increase i H c values for similar processing conditions [3]. Moreover, Zr additions in stoichiometric RE 2 Fe 14 B alloys have been reported as increasing the anisotropy field H A , since Zr enters the RE 2 Fe 14 B unit cell [4–6]. ∗ Corresponding author. Fax: +52-55-56161-371. E-mail address: israelb@correo.unam.mx (I. Betancourt). In this paper, the effect of processing conditions and Zr addition on the magnetic properties of RE-rich, Didymium (Nd/Pr) 14 Fe 80 B 6 (Nd:Pr ratio of 3:1) alloys, produced by direct quenching and by overquenching and annealing, is presented. 2. Experimental techniques Ingots of the alloys were prepared using commercial grade materials by arc-melting the constituents in a high purity Ar atmosphere. The compositions of the alloys were (Nd 0.75 Pr 0.25 ) 14 Fe 80-x Zr x B 6 (x = 0–4). Nanocrystalline directly quenched (DQ) ribbon samples with thicknesses and mean grain sizes in the range 20–40 m and 35–50 nm, respectively, were produced by chill block melt spinning at various roll speeds (16–25 m/s), under a protective argon atmosphere. Overquenched and annealed alloys (OA) were obtained by devitrification of fully amorphous alloy spun at 45 m/s (annealed 10 min at 700 ◦ C with material sealed in a silica tube under argon). The magnetic properties J r , i H c and (BH) max (computed from the BH loop) were determined using an Oxford Vibrating Sample Magnetometer with a maximum field of 5 T. Measurements were made in the 0925-8388/$ – see front matter © 2003 Published by Elsevier B.V. doi:10.1016/j.jallcom.2003.09.090