Effect of the laser fluence on the microstructure and the relating magnetic properties of BaFe12O19 films grown on YSZ(111) by PLD for optimized perpendicular recording

Abstract

High-quality BaFe12O19 (BaM) films with high uniaxial anisotropy fields of HA = 17.5 and 18.5 kOe were obtained by pulsed laser deposition (PLD) at two fluences of 1.5 and 5.1 J/cm2 on YSZ(111) substrate, using a platinum interlayer for reducing lattice mismatch. We demonstrated that the microstructure, morphology, and stoichiometry of the hexaferrite BaFe12O19 films can be affected by raising the corresponding energy per pulse from 25 to 75 mJ. However, we also concluded that the increase of fluence leads to the formation of a non-stoichiometric BaM film through two nucleation steps and an output growth of small grains in addition to the increase of the defect density. In turn, this has contributed to the enhancement of the coercive field from Hc = 1769 Oe to Hc = 2166 Oe as it is required for the improvement of perpendicular recording resolution. We found that both the lateral coherent block size and misorientation of mosaic blocks are remarkably affected by the growth kinetics, which itself depends on the energy per pulse. For a deep understanding of the effect of laser fluence on the microstructure, chemical composition, and on the magnetic properties of thin BaM films, the results of complementary methods are combined. These methods comprise high-resolution X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy (TEM), scanning TEM combined with energy-dispersive X-ray spectroscopy, and vibrating sample magnetometer. Graphical abstract

Effect of Underlayer Quality on Microstructure, Stoichiometry, and Magnetic Properties of Hexaferrite BaFe12O19 Grown on YSZ(111) by Pulsed Laser Deposition

“…Hexagonal barium ferrite (BaFe 12 O 19 , BaM) has attracted tremendous attention of several research groups because of their achievements in growing the c -axis perpendicularly oriented BaM thin films with a high anisotropy field H A and with a relatively high perpendicular coercivity Hc ⊥ , which could be usable for high-density perpendicular recording media . Several difficulties were encountered during the growth of BaM films by sputtering, − pulsed laser deposition (PLD), , molecular beam epitaxy (MBE), and others. These limitations included chemical intermixing between the BaM layer and the used substrates like SiO 2 , , SiC, MgO, Al 2 O 3 , and YSZ(111) .…”

“…Several difficulties were encountered during the growth of BaM films by sputtering, − pulsed laser deposition (PLD), , molecular beam epitaxy (MBE), and others. These limitations included chemical intermixing between the BaM layer and the used substrates like SiO 2 , , SiC, MgO, Al 2 O 3 , and YSZ(111) . It was demonstrated that a BaM recording layer with perpendicular easy magnetization was formed on a substrate by means of an underlayer that favors the BaM layer growth with the easy magnetization direction perpendicular to the substrate .…”

“…Furthermore, it is generally agreed that the nucleation sites are responsible for the lower measured coercivity . The type of defects and their formation mechanism in BaM film was not intensively investigated by means of high-resolution transmission electron microscopy (TEM) and complementary diffraction methods. ,, Nergis et al . demonstrated the existence of out-of-phase boundaries (OPBs) as a relevant defect type in BaM layers where the defect density depends on the laser fluence.…”

“…These limitations included chemical intermixing between the BaM layer 4 and the used substrates like SiO 2 , 1,7 SiC, 6 MgO, 4 Al 2 O 3 , 8 and YSZ(111). 5 It was demonstrated that a BaM recording layer with perpendicular easy magnetization was formed on a substrate by means of an underlayer that favors the BaM layer growth with the easy magnetization direction perpendicular to the substrate. 9 Several buffer layers, such as Au, 10 Pt, 1,2,4,11,12 Pd, 11 YSZ, 2 ZnO, 12 AlN, 13,14 TiO 2 , 3 and MgO, 4,7 were used to reduce the element interdiffusion between the substrate and the magnetic film.…”

“…19 The type of defects and their formation mechanism in BaM film was not intensively investigated by means of high-resolution transmission electron microscopy (TEM) and complementary diffraction methods. 5,20,21 Nergis et al 5 demonstrated the existence of out-of-phase boundaries (OPBs) as a relevant defect type in BaM layers where the defect density depends on the laser fluence. Jourdan et al 22 have demonstrated by simulation the efficiency of defects such as antiphase boundaries responsible for domain wall pinning, which enhances the coercivity field.…”