Abstract
In this study, [Fe 14 Å /Pd19 Å]5 and [Fe 3 Å /Pd 4 Å]5 thin films were grown at elevated temperatures by an ultra-high vacuum electron beam deposition on MgO (100) substrates. When [Fe14 Å /Pd19 Å]5 was prepared at 400 oC, the upper part of thin film remains layer structure indicating the intermixing phenomenon is not uniform through the elemental mapping analysis, and [Fe14 Å /Pd19 Å]5 film exhibits magnetic perpendicular anisotropy until the grown temperature is 600 oC. As [Fe 3 Å /Pd 4 Å]5 was prepared at 400 oC, [001] L10 FePd with perpendicular anisotropy and out-of-plane coercivity (Hc,) of 17504.7 Oe is obtained implying the intermixing phenomenon is improved. As, the prepared temperatures of [Fe 3 Å /Pd 4 Å]5 are 600 oC and 700 oC, the Hc, are 34007.0 and 600015.5Oe, respectively. One of the FePd films prepared at 700 oC was then post annealed at 700 oC for 5 hs, but Hc, drops apparently to 110011.9 Oe. As [Fe 3 Å /Pd 4 Å]5 prepared at 700 oC with and without post annealed, the L10 ratio are 0.94 and 0.71, respectively. In addition, Ku have less relevance to Hc, in FePd films. This results indicate both L10 ratio and Ku have less dependence on Hc, of FePd film here. FePd thin films are island structure and the grain boundary is composed of MgO (substrate), and average grain sizes were about 15-17 nm indicating similar grain sizes as prepared at 400 and 700 oC with or without post-annealing, respectively. Therefore, the effects of grain size and grain boundary can be rule out. Defects such as dislocation and stacking fault will be generated to reduce the mismatch strain during the growth process as thickness is about ~22 Å. According to the defect density analyzed by transimission electron microscopy, the stacking fault densities (ρS.F.) are closely related to Hc,, in addition Hc, and ρS.F. are increased as growth temperature raising. And, the ρS.F. are 1.050.04 nm-2 and 0.510.06 nm-2 as prepared at 700 oC treated without or with post annealing, respectively. Hc, is proportional to 〖ρ 〗_(S.F.)^1.5, indicating the strong pinning effect, therefore, stacking faults act as domain wall strong pinning sites and it will increase the resistance of magnetic domain wall motion during magnetization reversal, resulting in higher Hc,. By high angle annular dark field analysis, an intrinsic stacking fault was found and its bounded is composed of a pair of 1/2 <110> partial dislocations as FePd film prepared at 700 oC, showing total dislocation can be dissociated into stacking fault via climbing dissociation mechanism. Therefore, ρS.F. increase as growth temperature rising. As a FePd film was treated with post annealing, ρS.F. significantly decreases by 1/6 [112 ̅] and 1/3 [111] partial dislocations reacting with each other, leading to less strong pinning sites and lower Hc,. Because stacking faults acting as strong pinning sites, ρS.F. and Hc,can be manipulated via adjusting growth rate of [Fe 3 Å/Pd 4 Å]5 films. At lower growth rate (0.005 Å/s), the opportunity of partial dislocation interaction in FePd flm was raised, which is similar to FePd film treated post annealing, leading to lower Hc, (1400±12.0 Oe). Besides, it takes some time for dislocation dissociation by climbing, therefore, higher growth rate (0.03 Å/s) reduces climbing dissociation and ρS.F., causing lower Hc, (1920±7.3 Oe). (Therefore, an optimum value of Hc,exists at the moderate growth rate) To reducing ordering temperature, adding Cu3N layer or N2 in FePd film and then treated with post annealing are also studied. When adding thermal dissociated Cu3N layer to FePd film, which was prepared by electron beam deposition([Fe 3 Å/Pd 4 Å]4/Cu3N (15 Å)/ [Fe 3 Å/Pd 4 Å]) and treated post annealing for 20 min, L10 FePdCu phase is obtained. By high angle annular dark field analysis, Cu atom tends to occupy the Fe lattice site, therefore, the spin-orbital coupling between Fe and Pd is reduced, leading to soft magnetic behavior. [Fe 8 Å /Pd 4 Å]8 films with some nitrogen were prepared via sputtering and then treated with post annealing at 400 oC for 1 h. And, (111) oriented fcc FePd film with larger grain size is obtained as adding N2 or raising N2 ratio, indicating the addition of nitrogen can promote atomic inter-diffusion. But, FePd films with grain size about 3-8 nm are similar to the smallest thermal stable size (~5 nm) of L10 FePd, resulting in soft magnetic behavior.