P.A.I. Smith

Mechanically alloyed Sm(CoFe) permanent magnets

The use of mechanical alloying as a processing method for the solid-state synthesis of new materials has received considerable attention in recent years. Of particular interest has been the synthesis of rare earth permanent magnet materials. Many of the rare-earth transition metal alloys studied to date exhibit similar structures and properties in the as-milled condition. In particular, the hard magnetic phase does not form during mechanical alloying. Instead, either a single amorphous phase is formed or a two-phase mixture is developed during milling which consists of crystallites of the transition metal, (i.e. Fe, Co), and an amorphous phase containing the rare earth element. Crystallization of the as-milled structure into a nanocrystalline hard magnetic phase (i.e. Nd{sub 2}Fe{sub 14}B or SmCo{sub 5}) normally requires a heat treatment at temperatures in the range of 600--700 C. With Sm{sub 2}Fe{sub 17}N{sub 2.7}, nitriding must be carried out after crystallization since Sm{sub 2}Fe{sub 17}N{sub 2.7} decomposes to samarium nitride and {alpha}-Fe at temperatures above 500 C. Mechanically alloyed and heat treated structures have been found to exhibit remarkably high values of coercivity, H{sub c}. For example, values of H{sub c} exceeding 75 kOe have been obtained in SmCo{sub 5}.

Magnetic properties of mechanically alloyed nanocrystalline Fe25Cu75

Abstract Results of Mossbauer studies and magnetic measurements on mechanically alloyed Fe 25 Cu 75 , which show superparamagnetic behaviour of the supersaturated fcc-(Cu,Fe)phase are reported in this paper. The deviation of the magnetisation curves from the Langevin function at lower temperatures are probably due to interactions between Fe clusters.

Magnetisation processes and magnetic viscosity of mechanically alloyed SmCo5

Abstract Mechanically alloyed SmCo 5 materials with coercivities in the range of 50–75 kOe were studied in this work. Irreversible magnetisation processes were investigated by measuring remanences after initial magnetisation and after demagnetisation. A large deviation of the demagnetisation remanence from the Wohlfarth relationship indicated that interactions between grains play an important role in the irreversible magnetisation process. Viscosity tests showed nearly linear relationship between the magnetic field and the viscosity parameter for the initial magnetisation, while the viscosity was not strongly dependent on the field for the demagnetisation. High values of the viscosity parameter, Λ, between 120 to 220 Oe were measured at fields near coercivity.