Mechanically alloyed magnets SmCox (x=6.0–11.0) have been prepared using starting materials of commercial SmCo5 and Co powders. X-ray diffraction data indicate that the equilibrium Sm2Co17 phase can be achieved in a nanocomposite Sm2Co17/Co system at x=8.5–11.0, while a Sm2Co17/SmCo5 structure occurs at x=6.0–8.0. The best magnetic properties obtained at x=10.0 are as follows: (BH)max=10.2 MGOe, Br=9.4 kG, Hc=4.0 kOe, and S=0.82. Wohlfarth’s remanence analysis indicates that the high remanence can be attributed to the intergranular interaction between neighboring cobalt and Sm2Co17 grains.

We have investigated the effect of interfacial diffusion on the magnetic properties of Au∕Fe51Pt49 bilayer thin films. The samples were prepared in two stages. First, an ordered Fe51Pt49 continuous thin film was sputtered on a quartz substrate. Then an aurum cap layer was deposited onto the Fe51Pt49 film at room temperature, followed by a postannealing at 300–800°C to promote the interfacial diffusion. A high coercivity of 23.5kOe was achieved in the isotropic polycrystalline FePt-based film. Transmission electron micrographs indicate that the bilayer sample exhibits Ll0 ordered FePt grains with a diameter of about 20nm, which were partially isolated by Au phase. We consider that the isolation of FePtLl0 grains and the grain refining effect can be two contributory factors for the enhanced coercivity.

The crystal structure, microstructure, and magnetic properties for a series of Cu/ FePt bilayer films were investigated. The samples were prepared by depositing a Cu top layer on a highly ordered L1 0 FePt film. To promote interdiffusion, the bilayer samples were annealed at a temperature T d ranging from 300 to 800°C. X-ray diffraction data indicate that observable diffusion occurs at 400°C. The maximum coercivity thus obtained is 14.0 kOe, which is 24% larger than that of the ordered FePt film without a Cu top layer. The high H c can be attributed to the diffusion of copper atoms through the grain boundaries of the magnetic films, which may produce extra pinning sites for domain-wall movement. The ⌬M data measured from the Henkel plots of annealed Cu/ FePt films change from negative to positive values as T d is raised from 400 to 800°C. This can result from the effects of demagnetization coupling and exchange coupling and is further explained from the variation of squareness ratios of hysteresis loops.

The temperature relationship of the fluctuation field and coercivity in NdFeB alloys Coercivity of Ti-modified nanocrystalline (cu-Fe)-NdaFelaB alloys with soft iron particles embedded in hard Nd2Fe1,B matrix was studied. The alloys were prepared by melt spinning and annealing. The grain size of Nd,Fe,,B is from 20 to 60 run, while that of the soft iron particles is 11 to 30 nm. The coercivity of the annealed flakes decreased dramatically with increasing particle size of free iron, following the same tendency of a theoretical calculation by Schrefl et al. For the Ti-alloyed flakes, the 1 at. % Ti-containing ones show the highest coercivity of 11.1 kOe. Its (BH), value is about 16 MGOe despite lower Nd and B contents than stoichiometric Nd,Fer,B. More Ti addition would deteriorate the coercivity. 7072

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Magnetic properties and crystal structure of the Fe49−xCoxPt51 (x=0.0,0.7,1.3,2.2) thin films deposited on a quartz substrate heated at 500°C were investigated. A significantly enhanced energy product of 18.4MGOe (87% larger than that of the binary film) was obtained in the x=1.3 sample. This improvement can be attributed to the well exchange coupling between the Ll0 and the residual disordered FePt regions. Unlike the common exchange spring (coupled) magnets or films showing a well defined two-phase structure, the chemical ordering of Fe–Co–Pt films changes continuously from the ordered regions to the disordered regions. We consider that this continuous change of chemical ordering enhances exchange coupling. Furthermore, the addition of cobalt also accompanied the decrease of crystal domain (subgrain) size in FePt grains. The fine-grain dispersion also can be a reason for the high energy product.

Single layer CoPt thin films with thicknesses from 30to100nm were sputtered on glass substrates. A preannealing at 250°C for 80min was applied to the samples, before ordering treatment at 700°C for 10min. This preannealing process resulted in a 33%–65% decrease in coercivity and 23%–55% decrease in volume fraction of order phase f0. Results of morphology investigation showed that the preannealing increases the surface roughness, which mainly results from the elimination of defects. Structural results further suggest that the eliminated defects are mostly low dimensional, such as dislocations or vacancies. It can thus be concluded that those low dimensional imperfections in the CoPt films play an enhancing role in ordering transformation process.

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