On the role of Zn in Sm₂Fe₁₇N_x permanent magnets

Authors

• P.A.P. Wendhausen, Institute für Festköspes-und Weskstoffor-Schung Dresden e.v., PF, O-8027 Dresden, Germany
• D. Eckert, Institute für Festköspes-und Weskstoffor-Schung Dresden e.v., PF, O-8027 Dresden, Germany
• A. Handstein, Institute für Festköspes-und Weskstoffor-Schung Dresden e.v., PF, O-8027 Dresden, Germany
• K.-H. Müller, Institute für Festköspes-und Weskstoffor-Schung Dresden e.v., PF, O-8027 Dresden, Germany
• G. Leitner, Fraunhofer-Jesellschaft, Institut für Keramische Technologien und Sinterwerkstoffe, O-8020 Dresden, Germany
• Ralph Skomski, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

May 1993

Comments

Published by Am Inst of Physics. J. Appl. Phys. 73 (1993) 6044-6046. Copyright 1993. Permission to use. http://www.aip.org/.

Abstract

Coercivities up to 1.9 T were achieved by bonding micron-size Sm₂Fe₁₇N_x particles with zinc. X-ray analysis of Zn-bonded samples indicates the presence of the ZnFe Γ phase and no unreacted Zn, after heat treatment at about 390 °C for 100 min for samples with Zn content varying from 5 to 35 wt. %. The increase of coercivity occurs only for a more intense heat treatment, e.g., at 390 °C! for 300 min or 425 °C for 100 min. Differential scanning calorimetry (DSC) shows two exothermic peaks at 388 and 426 °C, but no endothermic peak related to the melting of Zn (at 419.6 °C) was observed. In dilatometric measurements two peaks were observed for the rate of length change near the same temperatures as the DSC peaks. Polarization-versus-field curves point to an additional ferromagnetic phase with (i) a Curie temperature near 180 K and (ii) 2% of the net magnetization at low temperatures. The corresponding dip in low-temperature demagnetization curves, however, is about 10% in depth. Most of the Sm₂Fe₁₇N_x grains in the demagnetized Zn-bonded masets are multidomain. We found γ ≈ 3.4≈ 1O^-2 J/m² and D_c≈0.3 μ m for the wall energy and for the critical single-domain particle diameter, respectively.