Perpendicular magnetic recording media with a high resolution and a low noise property were studied using a micromagnetic simulation. It was suggested that the introduction of a small separation between the adjacent grains is effective to obtain such media increasing the perpendicular M-H loop slope without increasing the domain size. The separation is thought to reduce the demagnetizing field acting on the magnetic grains increasing the M-H loop slope of the grains.
"Cross section TEM bright field image of [FePt(20 nm)/Fe(4 nm)]n multilayer films after annealing at 600 1C for 10 min. (a) n ¼1, (b) n¼ 2, and (c) n¼ 5. grains can be detected by the hysteresis loop slope at coercivity point, which is usually defined as α ¼ 4πðdM=dHÞ H ¼ Hc . Larger value of α indicates stronger inter-granular exchange coupling. "
[Show abstract][Hide abstract] ABSTRACT: Nanoparticle-FePt/Fe bilayer thin films with different Fe layer
thicknesses and [nanoparticle-FePt/Fe]n multilayer thin films
with various periods were fabricated by DC magnetron sputtering. Their
structures and magnetic properties (energy product and exchange
coupling) were investigated by X-ray diffraction technique and vibrating
sample magnetometer, respectively. The results show that coercivities of
FePt/Fe bilayer films are dropped from 10.7 kOe to 0.53 kOe with
increasing Fe soft magnetic layer thickness, due to the interconnecting
of FePt nano-particles by Fe-rich soft magnetic phase and decreasing of
the ordering degree of L10-FePt phase. The critical Fe layer
thickness changing the annealed film from granular to continuous
microstructure is about 4 nm. For multilayer [FePt/Fe]n
films, both ordering degree of L10-FePt phase and magnetic
properties are improved with the number of layer periods. Moreover, a
maximum energy products as high as 21.65 MGOe is obtained in the
[FePt/Fe]5 multilayer film. The enhancement of saturation
magnetization and energy products can be ascribed to the high ordering
degree of FePt phase as well as the strong exchange coupling among
L10-FePt hard magnetic phase and Fe-rich soft magnetic phase.
Journal of Magnetism and Magnetic Materials 11/2013; 345:165-170. DOI:10.1016/j.jmmm.2013.06.037 · 1.97 Impact Factor
"This suggests that there is a moderate intergranular exchange in our films. Regarding the correlation of with exchange, there are extensive discussions in  and . Because TEM pictures show well-isolated grains, the exchange coupling apparently occurs through the nonmagnetic metallic matrix (e.g., see the discussion in ). "
[Show abstract][Hide abstract] ABSTRACT: Highly textured  FePt:C nanocomposite thin films, deposited directly on thermally oxidized Si wafers, are obtained by multilayer deposition plus subsequent thermal annealing. Nanostructures, crystalline orientations, interactions, and magnetic properties are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic force microscopy, and magnetic measurements. The formation of the ordered L1<sub>0</sub> phase is confirmed by XRD, and only visible (00l) peaks indicate a high degree of the  texture. TEM observation reveals that FePt grains are embedded in the C matrix and appear to be well isolated. The FePt grains are very uniform with average sizes about 5 nm.
[Show abstract][Hide abstract] ABSTRACT: The slopes of the M-H loop of perpendicular magnetic recording media were estimated by micro-magnetic simulation for various inter-grain exchange couplings, grain aspect ratios and inter-grain spacings. The slope of the M-H loop depends not only on inter-grain exchange coupling but also on grain aspect ratio and inter-grain spacing. The simulation revealed that the required head field decreases with increasing inter-grain exchange coupling. The optimum value of the slope was slightly larger than 1.0 for compromising resolution and SNR by changing the inter-grain exchange coupling. The simulation results also indicated that the inter-grain spacing improves both resolution and SNR.
Japanese Journal of Applied Physics 09/2004; 43(9A):6052-6055. DOI:10.1143/JJAP.43.6052 · 1.13 Impact Factor
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