Magnetic Properties Study Of Nanocrystalline Cobalt and Cobalt-Based Alloys

Abstract

N.E. Fenineche1, O. El Kedim2, E.Gaffet2 1LERMPS/UTBM - F90010 - BELFORT CEDEX – France E-mail: Nour-eddine.fenineche@utbm.fr 2CNRS UMR 5060,UTBM, F90010 - BELFORT CEDEX - FRANCE Keywords : Ball milling, magnetic properties, nanostructures, coercivity, squareness ratio Abstract The effect of Ball milling parameters on the microstructure and consequently on the magnetic properties has been studied. The combination of low values of the plateau rotation and the high vial velocities w can enhance the cubic phase formation. Coercivity and crystallite size exhibit both a regular and similar diminution when plateau rotation velocity and mechanical alloying time are increasing. Introduction Ball milling (BM) is one of the possibilities to prepare materials with exceptional mechanical and magnetic properties. The objective of milling includes particle size reduction, mixing or blending, and particle shape change [1]. Because of the very fine grain sizes, nanocrystalline materials exhibit a variety of properties that are different and often considerably improved in comparison with those of conventional coarse-grained polycrystalline materials [2]. This change in the microstructure can affect mechanical and magnetic properties, particularly, coercivity, Hc, and squareness ratio, Mr/Ms, which are very important parameters from an industrial point of view [2,3]. Microstructural [4-6] and magnetic properties [7,8] of ball milled Co have been previously reported. In the case of cobalt based alloys, produced by mechanical alloying magnetic data on these powders shows behaviour typical of a soft ferromagnetic alloys [9]. This paper present the first results in our research group on the effect of three principle BM parameters : plateau rotation, vial rotation and ball-milling time on the microstructure and consequently on the magnetic properties. Experimental procedure Nanocrystalline Co and Fe-Co were produced by ball milling. Elemental powders, with an average particle size of 50 mm and a mean grain size estimated as 20 nm were introduced into a cylindrical tempered steel container (vial) of capacity 50 ml. Each container was loaded with three quenched steel (type 100C6) balls (diameter1.5 cm, mass 14g). The containers were sealed with a Teflon O-ring and the milling conducted in stationary air without exchange with laboratory atmosphere. The milling was carried out using the so-called G5 specially designed planetary high energy machine which allows the independent choice of the shock frequency and of the shock energy [10,11].