Preparation,Characterization And Magnetic Properties Of Anisotropic SmCo₅/FeCo Nanocomposite Powder

The rare-earth permanent magnets with high residual magnetic induction,large coercive force,and maximum magnetic energy product provide excellent conditions for manufacturing various tiny magnetic functional devices.SmCo₅,the first-generation rare-earth permanent magnets has high anisotropy,high coercivity,and low temperature coefficient,providing important application prospects in many fields.However,the magnetic properties of SmCo₅ are relatively low compared to other permanent magnets such as second generation rare earth permanent magnet Sm₂Co₁₇ and third generation rare earth permanent magnet Nd₂Fe₁₄B,limiting the scope of its applications.The nanocomposite permanent magnet material is a strong magnetic coupling system at the nanometer scale by using a magnetically hard phase with high coercive force and a magnetically soft phase with high saturation magnetization,thereby achieving high saturation and high coercivity.In this paper,a high coercivity SmCo₅ hard magnetic phase powder and an FeCo soft phase with high saturation magnetization were selected.A series of nano-duplex composite powders were prepared by chemical synthesis.The effects of reaction conditions on the morphology and magnetic properties of the samples were studied.1.Effect of experimental parameters on morphology and properties of composite powders.Surfactant-assisted high-energy ball milling was used to prepare SmCo₅ flake particles with strong anisotropy as magnetically hard phase.The surface of the flake particles was coated with a dense layer of FeCo soft phase,producing effective exchange coupling in the hetero-SmCo₅/FeCo dual-phase nanocomposite powder.The reaction conditions have substantial effect on the chemical deposition process of soft phase.An addition of polyvinyl pyrrolidine?PVP?with a larger mass fraction and a reaction heating method with good thermal insulation effect were used to optimize the size and coating of the soft phase;The pickling time and reaction time improve the shoulder collapse problem without affecting the magnetic properties of the nanocomposite powder.The grain size and structure of the samples were studied by using an X-ray diffractometer.The morphology of the powder was observed by using field emission scanning electron microscopy.The magnetic properties of the powder were obtained by using a vibrating sample magnetometer.2.Effect of soft magnetic phase precursor addition on morphology and properties of composite powders.The SmCo₅/FeCo nano-duplex composite powder prepared in the experiment still has the strong anisotropy as it in the original powder.With increasing mass ratio of the FeCo soft phase,the exchange coupling effect and the remanence enhancement effect occur.When the soft magnetic phase feed ratio is10 wt.%or more,the FeCo particle deposition rate is increased and a dense granular film is formed.When the feed ratio is 10 wt.%,the magnetic properties are optimal,and the hysteresis curve does not show collapse.The soft magnetic phase average particle size is 10.5 nm,the maximum magnetic energy product is 204.5 kJ/m³,and the saturation magnetization is increased to 101.6 Am²/kg.The remanance is 97.3Am²/kg and the coercive force is 1.69 T.When the feed ratio is 15 wt.%,the average particle size of FeCo particles with large particle size and uneven size is 16.7 nm,decoupling occurs between soft and hard magnetic phases.3.Effect of the type of surfactant on the morphology and magnetic properties of composite powder.When oleic acid is used as a surfactant,it is easy to prepare soft magnetic phase particles having a small size of about 5 nm.Changing the amount of oleic acid added is conducive to the deposition of soft magnetic phase,and the magnetic properties of the nanocomposite powder were also increased.When the feed ratio of the soft magnetic phase precursor was changed to 15 wt.%,the demagnetization curve shows no collapse phenomenon,the maximum magnetic energy product reached a maximum of 235.6 kJ/m³,the saturation magnetization was 103.9 Am²/kg,and the remanence was 101.2 Am²/kg.The coercive force is 1.72T,and a nanocomposite magnetic material having high coercivity and high saturation was prepared.