Raman study across Verwey transition of epitaxial Fe3O4 thin films on MgO (100) substrate grown by pulsed laser deposition

Abstract

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.

Raman study of ultrathin Fe3O4 films on GaAs(001) substrate: stoichiometry, epitaxial orientation and strain

“…Therefore, it is necessary to seek a powerful technique to quickly and convincingly probe the structural properties of ultrathin Fe 3 O 4 films on semiconductor substrates, which is not well established yet. In fact, Raman spectroscopy on Fe 3 O 4 has played an important role in researches on steel corrosion, [20,21] identification of iron oxides [22] and physical properties of Fe 3 O 4 such as Verwey transition [23] and antiphase boundaries. [24] Here, we show that Raman spectra can be employed to in situ monitor the Fe 3 O 4 film formation and determine the epitaxial orientation and strain of these ultrathin Fe 3 O 4 films with thicknesses less than 20 nm.…”

Synthesis and Characterisation of Hollow Spherical Nano- and Microparticles with Silica and Magnetite

“…It is known [26,27] that the dielectric-metal phase transition takes places for Fe 3 O 4 at T = 119−123 K. At T ≈ 300 K it is in the metallic state and has the electrical conductivity σ = 10 3 −1 cm −1 . In the case of the spherical magnetite particles, the dc conductivity is low since σ = 10 −6 −1 cm −1 .…”

Raman spectroscopy indications of the Verwey transition in epitaxial Fe3O4(111) films on Pt(111) and Ru(0001)

“…However, at~120 K it undergoes a phase transition -the so called Verwey transition [2], during which significant changes in structure (from cubic to monoclinic below the Verwey temperature (T V )), conductivity (metal-insulator) and magnetic properties (change of magnetization) occur [1]. For different forms of magnetite, such as nanocrystals/nanoparticles or thin films, the temperature at which the Verwey transition occurs, as well as the character of the changes, may slightly differ [3][4][5][6][7].…”

“…Temperature-dependent Raman spectroscopy is one of the methods that can be used for studying the Verwey transition in thin magnetite films [5][6][7]. In contrast to "classical" methods of the Verwey transition investigation, such as resistivity/magnetoresistivity measurements or vibrating sample magnetometry, which are particularly unsuitable for studying thin films on metal supports, Raman spectroscopy is a surface sensitive technique in which the measured signal is not dominated by the contribution from the bulk substrate.…”

“…Magnetite films can be epitaxially grown on various single crystal supports, such as MgO(100) [5][6][7], Al 2 O 3 (0001) [6,7], Pt(111) [8] or Ru(0001) [9]. Depending on the level of epitaxy with the support, the films can be stoichiometric and structurally well-defined or strained and defected.…”