Alloys with Compositions Co-25.5wt/o Sm-Sw/o Cu-15 w/o Fe-3w/o Zr and Co-Sra-Cu-Fe-1.5 w/o Zr have ibeen step aged to produce magnets with coercive force (iHc) in the range of 10-25k0e, much higher than those reported so far in the litera ture for the Zr alloys. The high coercive force magnet s are typically aged at 800-850°C for 10-30 hours following the solution treatment at 1150°C. Subsequently, these are step aged to produce materials with high coercivity. The microstructure in all these alloys has a 2 phase cellular morphology with 2:17 phase surrounded by a 1:5 boundary phase. The long aging treatments at 800-850°C lead to coarsening of the two phase structure. The subsequent stepaging does not change the morphology, but only changes the chemical composition of th:* two phases.Best properties are obtained in materials with a cohe rent microstructure of optimum boundary phase thickness and optimum chemical composition. The highest values of iHc ob tained so far are % 26k0e and a. 16 kOe for the 3% Zr and 1.52 Zr alloys respectively. The (best hard magnetic properties of (B?0 max = 33 MGOe and iHc = 13k0e are for a 25% Sm-20%Fe-4 Cu-2%Zr alloy.

Uni-axial anisotropy constants and uni-axial anisotropy fields of oriented polycrystalline magnets were obtained from the field-dependence of the magnetization by three methods and from torque measurements. The results from torque measurements are found to be superior to those from the intersections of magnetization curves for fields parallel and perpendicular to the preferred axis, the integral of the perpendicular magnetization and the maximum in the second derivative of the perpendicular magnetization, called the singular point detection (SPD) method. Sintered Sr ferrite magnets can be considered as quasi-single crystals because of their high degree of orientation and their large crystal grain sizes in the range . A value of was obtained by extrapolation to high field of the term determined by Fourier analysis of unsaturated torque curves. This is closer to the result for single crystals than the other methods. The SPD method was used to analyse data recorded in high pulsed fields to determine the large values of for sintered Nd - Dy - Fe - B magnets with various compositions. There is an increase in that is linear in the Dy content.

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