Study On The Preparation And Magnetic Properties Of Sm-Co Based Composite Nanoparticles

The development of rare earth metal permanent magnetic material has experienced three generations:SmCo₅,Sm₂Co₁₇,Nd₂Fe₁₄B.In order to make the magnetic materials get more excellent performance,the nanocomposite materials derived from the concept of exchange coupling became the research foucus.In this paper,the composite magnetic nanoparticles with Sm-Co as the hard magnetic phase and Co or Fe-Co as the soft one were synthesized by the chemical reduction methods such as the electroless plating,sol-gel and solvothermal methods.The microstructure and magnetic properties of the obtained particles were characterized by the FTIR?XRD?TEM and VSM instruments.Meanwhile,the formation and magnetic mechanism of the particles were studied,which provided a new idea of synthesizing composite magnetic materials with excellent magnetic properties.it was found:?1?Pure Co and Sm-Co/Co composite particles were prepared by the electroless plating method with the assistance of water bath heating.The roles of different solvents,such as DIW,EtOH and EG on the reduction of Co²⁺were investigated comparatively.The chemical mechanism for the formation of Co in EtOH and EG systems was studied by FTIR.After introducing Sm-Co particles into the above EG system,Sm-Co/Co composite particles were synthesized.When the heating time is prolonged to 4 h,relatively strong exchange coupling interaction can take place between the hard and soft phases,and relatively higher magnetic properties,such as Hci=1623.7 Oe,Mr/Ms=0.371 can be achieved.?2?Fe³⁺and Co²⁺were introduced into the precursor solutions together,hereafter,Fe-Co particles was prepared by the liquid reduction method with the assistance of water bath heating.Fe-Co alloys with different compositions and phase structures were obtained by changing the molar rations of Fe³⁺:Co²⁺.When the molar ratio of Fe³⁺:Co²⁺in the precursor solution is 7:3,Fe₇Co₃ with high purity and good soft magnetic properties can be obtained.On this basis,Sm?Co,Hf?₇CNTs_0.05/Fe-Co composite particles were synthesized by introducing Sm-Co particles with the electroless plating method,whose major magnetic parameters were as follows:Hci=1074.4 Oe,Mr/Ms=0.203.?3?Pure Co particles which exist in fcc-and hcp-crystal structures and Sm-Co/Co composite particles can be achieved by the sol-gel method with Co?acac?₂ as the source of Co.The magnetic properties of Sm-Co/Co composite particles are:Hci=899.7Oe,Mr/Ms=0.236.?4?Pure Co particles which exist in fcc-and hcp-crystal structures were prepared in EG system by the solvothermal method.When the concentration of Co²⁺in the precursor solution is 0.01 mol/L,and the molar ratio of Ag⁺:Co²⁺is 1:100,soft magnetic Co particles smaller than 100 nm can be obtained at the solvothermal temperature of 160°C.After introducing Sm-Co particles into the above system,Sm-Co/Co composite particles were synthesized,in which Co particles of about 20 nm can be observed in the surface of Sm-Co particles.These Sm-Co/Co composite particles show the following magnetic properties:Hci=618.6Oe,Mr/Ms=0.221.