Study On The Structure,magnetic Properties And Element Doping Effects Of Electrodeposited L1₀ FePt Films

In recent years,the chemically ordered face-centered tetragonal?fct or L1₀?Fe Pt alloy is considered to be a very promising permanent magnetic material due to its very high magnetocrystalline anisotropy,which can be used for high-density magnetic storage and microelectromechanical System?MEMS?.Generally,in MEMS,thick and continuous films are required.Fe Pt films are mainly prepared by various deposition techniques.The advantage of electrodeposition is that thicker films can be produced more efficiently and cheaply.In the electrodeposition method,the deposited film needs to be annealed at a high temperature to form a high-coercive L1₀ phase.Annealing is essential for forming the L1₀ ordered phase and its magnetic properties.However,the influence of annealing conditions on the phase transformation,microstructure and magnetic properties of Fe Pt films has not been well studied.For example,the mechanism behind the"shoulder collapse"phenomenon found in hysteresis loops in the previous electrodeposited Fe Pt films has not been fully explained.This article explores the effects of substrate selection,bath composition,annealing conditions,and doping on the morphology,structure,and properties of L1₀ Fe Pt.The main contents are as follows:?1?Base selection.The effects of Cu,Si,and Ag on the preparation of Fe Pt films on their morphology,structure,and magnetic properties were compared,and Ag was determined to be the best substrate for preparing Fe Pt films.By adjusting the p H of the plating solution and the deposition potential,the preparation conditions of p H 2.8 and potential-0.9 V were determined.After deposition for 30 min,Fe₄₈Pt₅₂ was obtained.?2?Preparation and magnetic properties of Fe Pt thin films.Comparing the effects of different annealing temperature and time on the morphology,structure and magnetic properties of the Fe Pt film,it is concluded that the film obtained by electrodeposition contains a large amount of oxygen elements,which is an amorphous/nanocrystalline structure and exhibits soft magnetic properties.After annealing at high temperature,the Fe Pt film gradually changed to the L1₀ Fe Pt phase,and the coercivity increased rapidly,reaching 15 k Oe.Gaussian fitting of the grain size shows that the size is about 5.4 nm and the grain distribution is uniform without overlapping.In addition,through the simulation of soft magnetic and permanent magnet curves,the"shoulder collapse"behavior of the hysteresis loop was successfully explained.?3?Preparation and magnetic properties of B-doped Fe Pt thin films.The layered deposition of[Pt/Fe_xB]_n was successfully prepared by electrochemical method.After annealing,the L1₀ Fe Pt B phase was successfully synthesized,and the thin film prepared by this method was conducive to?001?crystal plane growth orientation.Through investigation,it is found that the addition amount of Na BH₄ at the best magnetic performance is 0.3 g/L,and the value of x obtained by the test is about 3.The study shows that the number of thin film layers when the magnetic properties are the best is four,which not only enhances the growth of the?001?crystal plane and the coercive force reaches 23 k Oe at the maximum.The analysis shows that a small part of the B element enters the lattice gap,and most of it is located in the grain gap,which isolates the mutual interference between the grains,helps to refine the Fe Pt grains,and effectively improves the magnetic properties of the film.?4?Preparation and magnetic properties of Fe_xCo_1-xPt ternary alloy film.Fe_xCo_1-xPt ternary alloy thin films were successfully prepared by adding different amounts of Co²⁺to the plating solution to gradually replace Fe²⁺.The deposited film is still a disordered fcc phase,which changes to L1₀ phase after annealing,but because Co atoms replace the lattice positions of Fe atoms,and its atomic size is smaller than Fe atoms,the characteristic diffraction peak of the film shifts to a large angle.Hysteresis loop test shows that the coercive force of undoped Fe Pt and Co Pt films is significantly greater than that of doped Fe_xCo_1-xPt films.In addition,the easy magnetization axes of the films prepared by co-deposition are all in parallel directions.