Barium hexaferrite (BaFe12O19 or BaM) films were grown on c-plane sapphire (0001) substrates by pulsed laser deposition (PLD) to evaluate the effects of laser fluence on their composition, structure, and magnetic properties. A Continuum Surelite pulsed 266 nm Nd:YAG laser was employed, and the laser fluence was varied systemically between 1 and 5.7 [J/cm 2 ]. Deviations from the stoichiometric transfer between the BaM targets and deposited thin films occurred as the laser fluence changed. The Fe to Ba ratio in the films increased with laser fluence. The films deposited at laser fluences below 4 J/cm 2 showed undesirable 3-dimensional island growth.Moreover, insufficient laser energy resulted in the deposition of some secondary phases, for example, Barium monoferrite (BaFe2O4) and Magnetite (Fe3O4). Alternatively, laser fluences above 5 J/cm 2 promoted resputtering of the growing film at the substrate and degraded film quality, structure, and magnetic properties. BaM films deposited at 4.8 J/cm 2 -the optimal laser fluenceshowed excellent c-axis orientation perpendicular to the film plane with an anisotropy field of 16 kOe and saturation magnetization of 4.39 kG. These results clearly demonstrate a strong influence of laser parameters on PLD-grown hexaferrite films and provide a path for high-yield production using pulsed laser depositions systems.
In the past decades, ferromagnet-metalloid alloy films of Co-Fe-B have been widely used in new magnetic devices due to their excellent performance, such as easy industrial-scale fabrication, and considerable ability for tunneling magnetoresistance and perpendicular magnetic anisotropy. However, the insufficient thermal tolerance and interfacial state densities in the typical CoFeB/MgO system limits devices optimization. Because of the improvement in thermal stability and interfacial properties by carbon element replacement, new theoretical and experimental work on Co-Fe-C alloy film properties have been reported. Here, we report on the magnetostrictive behavior, soft magnetism and microwave properties of a series of (Co 0.5 Fe 0.5) x C 1-x films grown on silicon (001) substrates. The addition of carbon changes the Co-Fe-C films from nanocrystalline bcc to an amorphous phase and leads to a high saturated magnetostriction constant of 75 ppm, high piezomagnetic coefficient of 10.3 ppm/Oe, excellent magnetic softness with a low coercivity less than 2 Oe, narrow ferromagnetic resonance linewidth of 25 Oe at X-band, extremely low Gilbert damping of 0.002 and up to 500℃ thermal stability. The large saturated magnetostriction constant and piezomagnetic coefficient result from coexistence of nanocrystalline bcc and amorphous phases. The extremely low Gilbert damping is related to the minimized density of states around Fermi energy of the alloys induced by carbon doping. The combination of these properties makes Co-Fe-C films a promising candidate to be widely used in voltage tunable magnetoelectric devices and microwave magnetic devices.
High‐frequency ferrite ceramics exhibiting high permeability and low magnetic loss have been recently attracting more and more attention owing to the rapid development of modern communication technologies. It is known that the magnetic performance of ferrites is strongly associated with the morphology of their polycrystalline structure. In this work, we focus on the control of grain growth and densification process for planar Co‐Ti doped M‐type barium hexaferrites, BaCoxTixFe12‐xO19, by one‐step sintering (OSS) and two‐step sintering (TSS) techniques. Experimental results indicate that a uniform and fine‐grained microstructure is achieved by the TSS method. More importantly, the ferrites prepared by TSS demonstrate high permeability (µ' = 18‐20), low magnetic loss (tan δm = 0.1‐0.3), and high Snoek's product (>25 GHz) in the frequency range of 100‐400 MHz. By fitting experimental data, we have determined that low magnetic loss is derived from the small damping coefficient of spin rotation in terms of Kittel's theory. Therefore, the TSS technique provides an effective and efficient approach to prepare planar BaM hexaferrite materials for ultra‐high frequency (UHF) communication devices requiring low loss and high Snoek's product.
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