Evolution of properties of epitaxial bismuth iron garnet films with increasing thickness

Curie temperature, exchange integrals, and magneto-optical properties in off-stoichiometric bismuth iron garnet epitaxial films

“…Figure 8 shows the specific Faraday rotation for all films in the spectral range of 1.9 to 2.4 eV. Films B, D, and E exhibit the same spectral variation with a pronounced peak at ϳ2.32 eV, whereas this peak occurs at lower energies of ϳ2.27 eV for films A and C. It must be pointed out that films A and C are somewhat thicker than films B, D, and E. A qualitatively similar red shift was observed by Kahl et al 25,26 when increasing the thickness of BIG films grown in otherwise identical conditions. These authors could not identify the cause of this apparent thickness dependence of the red shift, although a possible correlation with the x-ray coherence length was detected by x-ray diffraction.…”

“…1 for film C. This confirms that the garnet phase is obtained for a rather large range of experimental conditions as reported by most other authors. 26,30 Tepper et al 28 reported a narrower window of deposition conditions, maybe due to the fact that they used a low laser energy density for the deposition ͑1.4 J / cm 2 ͒. Traces of BiFeO 3 are observed in films A, C, and E. Slightly more intense BiFeO 3 peaks are found in film D. Adachi et al 22 also detected a weak BiFeO 3 peak in films grown by PLD with oxygen pressure above 30 mTorr.…”

“…Since some BiFeO 3 was detected by x-ray diffraction, the Bi/Fe ratio in the garnet phase could be somewhat overestimated especially for film D. These RBS stoichiometry data suggest that films deposited from the stoichiometric target ͑films A, B, and C͒ are strongly Bi-deficient as also observed by other authors. 26,39 Films D and E were grown from targets containing a bismuth excess and have a Bi/Fe ratio close to the nominal value of 0.6.…”

“…[11][12][13][14][15][16][17][18][19] However, studies on the role of bismuth in iron garnets have long been confined to compounds with relatively low bismuth content because the pure bismuth iron garnet Bi 3 Fe 5 O 12 ͑BIG͒ does not exist in bulk form ͑due to the large ionic radius of the Bi 3+ cation͒ and cannot be grown by liquid-phase epitaxy ͑LPE͒. Since 1989, several authors have shown that BIG can be grown as a thin film on suitable garnet substrates by pulsed laser deposition ͑PLD͒, 4,6,18,[20][21][22][23][24][25][26][27][28] reactive ion-beam sputtering ͑RIBS͒ ͑Refs. 29-31͒, or other vapor deposition techniques.…”

“…22,23,28,[30][31][32][33]37 However, another important issue is the stoichiometry of the films: contrary to liquid phase epitaxy, vapor phase deposition techniques, such as used to grow BIG films frequently yield off-stoichiometric films, 38 and the reported Bi/Fe ratios vary indeed in a wide range ͑from 0.48 to 0.66͒. 22,26,28,30,33,34,39 In the present paper we study the effect of variations to the stoichiometry of bismuth iron garnet thin films on the magnetic and magneto-optical properties. We report on the temperature dependence ͑100-700 K͒ of the Faraday rotation and ellipticity at a photon energy of 2.25 eV for BIG films grown by PLD under different oxygen pressures and from targets of different compositions.…”