Heteroepitaxial Barium Hexaferrite Films on (111) Magnesium Oxide Substrates
- PDF / 796,017 Bytes
- 6 Pages / 391.5 x 607.5 pts Page_size
- 37 Downloads / 222 Views
Another promising substrate for this application is magnesium oxide (111), which has a face centered cubic (fcc) structure such that the continuity of close-packed oxygen planes across the interface serves as a template for an (001) BaFe 120 9 film. Here the room temperature lattice parameter of MgO is slightly larger than that of BaFe12O1 9, with a lattice mismatch of-1% [4][5], and, most importantly, the BaFe1 2O1 9 film will be under compression since the thermal expansion coefficient of MgO is greater than that of BaFe1 2O1 9 [6][7]. Here we present results on the growth and characterization of epitaxial BaFe1 20 9 (001) films on MgO (111) substrates for application in planar microwave devices. EXPERIMENT The barium hexaferrite films characterized here were deposited onto optically polished MgO (111) substrates by pulsed laser ablation deposition using a Compex 205 KrF excimer laser (k = 248 nm) at an energy density of 4 -5 J/cm 2 and a repetition rate of 50 Hz. For the thicker films discussed here, three 2 in. diameter targets of pressed and sintered BaFe,20 9 were used in a rotating target carrousel, such that they could be rotated and rastered to maximize target surface usage. The ambient oxygen pressure was set to the optimal pressure (20 mTorr) found for growing thick BaFe12O19 films on A120 3 (001) substrates.[l][8] The substrate temperature was set at 925°C, where both an in situ halogen lamp and a conductive heater were used to maximize the film surface temperature throughout the deposition. Films were deposited having thicknesses of from -1 micrometer to over 30 micrometers, with selected films being characterized by x-ray diffraction, magnetometry, and ferrimagnetic resonance measurements. RESULTS Our initial depositions have demonstrated that barium hexaferrite films can be deposited onto MgO substrates to a thickness of almost twice that attainable on sapphire without fracture in either film or substrate, and with the film retaining good c-axis texture and excellent magnetic properties. Figure 1 shows an electron micrograph cross-section of a 32 rtm BaFe1 20 9 film on a MgO substrate, where the sample was fractured along the cleave planes of the substrate, which are not perpendicular to the surface. Here, the torn film is shown to be very dense, with surface outgrowths of order a few microns in height scattered on the top surface.
Figure 1 Cross-section of a 32pim thick epitaxial BaFe1 2O19 / MgO film.
138
The film texture and c-axis lattice parameters were found from x-ray diffraction measurements, with the results for two films of thickness 14 jtm and 28 jim being shown in Figure 2. Both films display excellent c-axis texture, as shown by the presence of all of the dominant (O0n) diffraction peaks in the spectra, with only a few peaks corresponding to non-caxis oriented crystal planes being apparent in the thicker film [4][5]. It has been noted that diffraction patterns taken on films having a thickness near 30 gtm show a considerable reduction in intensity compared to that of the 15 jim films
Data Loading...
