L Journal of Alloys and Compounds 275–277 (1998) 660–664 Orientation of samarium–cobalt compounds by solidification in a magnetic field a, b a a * B.A. Legrand , D. Chateigner , R. Perrier de la Bathie , R. Tournier a Laboratoire EPM-MatForMag, CNRS, 25 Avenue des Martyrs, 38042 Grenoble, France b ´ ´ Laboratoire de Physique de l’ etat condense, Univ. du Maine, BP 535, 72085 Le Mans, France Abstract The solidification from the liquid state in a magnetic field produces oriented polycrystalline materials. A high degree of orientation is obtained with Sm–Co compounds solidified in several Tesla. The samples are crystallographically oriented with their easy-magnetization axes lying along the direction of the magnetic field applied during solidification. The process can be applied to the production of bulk anisotropic permanent magnets, without using the powder metallurgy. A model, validated by experimental results in the case of Sm–Co alloys, is proposed to explain the orientation mechanism.  1998 Elsevier Science S.A. Keywords: Orientation; Anisotropy; Solidification in a magnetic field; SmCo; Permanent magnet 1. Introduction metal, the ferromagnetic phases SmCo (1:5) and Sm Co 5 2 17 (2:17) are combining high saturation magnetization (J 5 s 1:5 The application of a static magnetic field of several 0.95 T and J 51.4 T at room temperature), high Curie s 2:17 Tesla during the solidification of some alloys can favour temperature ( T 57108C and T 59178C), with a large c c 1:5 2:17 their crystallographic orientation. This is the case of the uni-axial magnetocrystalline anisotropy along the crystallo- paramagnetic YBa Cu O ceramic which can be ori- graphic c-axis. The crystal structure of the SmCo phase is 2 3 72d 5 ented by cooling from the liquid state in a magnetic field hexagonal (CaCu -type). The structure of the Sm Co 5 2 17 21 of 5 T, at a rate of 208Ch to allow the peritectic reaction phase can be generated from that of SmCo by an ordered 5 of the compound [1]. substitution of Co dumb-bells into some of the Sm sites. The aim of this paper is to show that solidification in a Consequently, these two phases are crystallographically magnetic field of the intermetallic compounds SmCo and coherent and particularly have the same easy-magneti- 5 Sm Co produces oriented polycrystals, even in extreme zation axis (the c-axis) [2]. The study of the binary Sm–Co 2 17 solidification conditions such as high cooling rate or strong phase diagram [3] shows that SmCo forms from the liquid 5 and uncontrolled thermal gradients. The resulting high and Sm Co ( T 512908C and T 5 2 17 melting melting 1:5 2:17 degree of orientation is used in two ways. First, the process 13408C). is applied to the production of bulk oriented Sm–Co The Sm–Co type permanent magnets are based on these permanent magnets. Secondly, the results validate a model two ferromagnetic phases. In particular, the fine-scale which explains the physical orientation mechanism which microstructure of the ‘2:17’ industrial magnets consists of occurs during the solidification process. a network of 2:17-type phase cells (with a size of 100–200 nm) separated by a coherent 1:5-type boundary phase (5 to 20 nm) [4]. These ‘2:17’ magnets are not binary com- 2. Experimental details pounds but also contain copper (5 to 8 at. %), iron (17 to 28 at. %) and zirconium (1 to 3 at. %) substituting cobalt 2.1. Materials atoms. Their composition is Sm(Co, Cu, Fe, Zr) . z 57 to 8.5 The value of z determines the relative amount of the 2:17 Due to the association of a rare earth and a transition and 1:5 phases. Fortunately, these substitutions do not radically affect the crystal structure and do not change the * c-axis anisotropy. The magnetic properties of these ‘2:17’ Corresponding author. Tel.: 133 047 6887428; fax: 133 047 6881191; e-mail: legrandb@labs.polycnrs-gre.fr substituted compounds are adapted to permanent magnet 0925-8388 / 98 / $19.00  1998 Elsevier Science S.A. All rights reserved. PII: S0925-8388(98)00414-9