We have deposited magnetite thin films using the pulsed laser deposition technique from a α-Fe2O3 target on different substrates (Si (1 1 1), GaAs (1 0 0), Al2O3 (0 0 1) and amorphous float glass (FG)) without any buffer layer at a substrate temperature of 450 °C. These films have been characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, ac magnetic susceptibility and four-probe resistivity. The XRD results of these films show highly (1 1 1) oriented growth and single phase nature of Fe3O4 films on all substrates. Fe 2p core level x-ray photoelectron spectra and Raman spectra reveal the formation of Fe3O4 throughout the thickness of the films. All films show a Verwey transition at or around 120 K. It is observed that the oriented growth of Fe3O4 films takes place along the [1 1 1] direction on these substrates, which have either a huge lattice mismatch or no matching at all (as in FG) with Fe3O4.

We present a Raman study of Fe3O4 (100) thin films across the Verwey transition in the temperature range of 85–300K. These films are epitaxially grown on MgO (100) substrate by pulsed laser deposition technique. X-ray diffraction and low temperature resistivity measurements reveal that these films exhibit high structural order and perfect stoichiometry with Verwey transition at 121K. The frequency of different Raman modes [A1g and T2g(2)] changes abruptly around the Verwey transition temperature (TV). Below TV we observe a splitting in T2g(3) mode. Using Allen’s formula [Solid State Commun. 14, 937 (1974)] the strength of the electron-phonon coupling (λ) is estimated from the observed line shape parameters, and our estimates show that in epitaxially grown Fe3O4 thin films strong electron-phonon coupling is present. This coupling parameter is larger for T2g(3) mode as compared with that of A1g and T2g(2) modes. It is also observed that the coupling parameter corresponding to A1g mode remains invariant going from bulk single crystal to thin film while that of T2g(2) and T2g(3) modes are almost doubled. An attempt has been made to correlate the observed behavior with the presence of antiphase boundary in epitaxial thin films.

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Thin films of magnetite (Fe 3 O 4 ) are grown on single crystal GaAs (100) substrate by pulsed laser deposition. X ray diffraction (XRD) result shows the (111) preferred orientation of the Fe 3 O 4 film and x-ray photoelectron spectroscopy confirm the presence of single phase Fe 3 O 4 in the film. The electrical transport property of the film shows the characteristic Verwey transition at 122 K and below 110 K, the transport follows variable range hopping type conduction mechanism. The film shows room temperature magnetization hysteresis loop suggesting the ferrimagnetic behavior of the film with saturation magnetization value close to 470 emu/cc. PACS Nos.: 75.50.Gg, 73.61.-r, 75.47.-m a Corresponding author e mail: dmphase@csr.ernet.in

We report the element specific polarized near edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments on well characterized undoped MoO2 thin films that show ferromagnetism at room temperature. The polarization dependent of O K edge NEXAFS spectra indicate a strong hybridization of O 2p-4d Mo orbitals followed by a strong anisotropy in the electronic properties. An unquenched orbital magnetic moment within the O 2p shell is clearly evident from the XMCD O K edge, which is ferromagnetically coupled to the neighboring Mo moments as confirmed by Mo M3,2 edge XMCD experiment.