Temperature and terahertz frequency dependence of the dielectric properties of Fe3O4 thin films deposited on Si substrate

The Fe$_3$O$_4$/Si films are considered to be promising materials for THz spintronic applications due to their high temperature magnetic transition and semiconducting properties. In this article, we present the real part of the dielectric constant ($\epsilon_1$) and the optical conductivity ($\sigma_1$) of Fe$_3$O$_4$ films of different thicknesses deposited on Si substrate (Fe$_3$O$_4$/Si) in the THz range at temperatures 2- 300 K. Although the magnetization of the films with thickness $\geq$ 115 nm shows a clear change at the Verwey transition temperature T$_v$ = 121 K, their optical properties in the THz frequency range are drastically different from each other. We have shown that $\sigma_1$ is maximum and $\epsilon_1$ is minimum when the Fe$^{+2}$/Fe$^{+3}$ ratio is equal to 0.54 which is the ratio of Fe+2/Fe+3 for pure Fe$_3$O$_4$. The $\sigma_1$ reduces and $\epsilon_1$ increases at all temperatures when the Fe$^{+2}$/Fe$^{+3}$ ratio deviates from 0.54. We have shown that a slight change in the Fe$^{+2}$/Fe$^{+3}$ ratio can induce large changes in the optical properties which shall have implications in the application of the Fe3O4 films in THz spintronics.Comment: 18 pages, 6 figure

Robust perpendicular magnetic anisotropy in Ce substituted yttrium iron garnet epitaxial thin films

Cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films are prepared on gadolinium gallium garnet (GGG) substrate with pulsed laser deposition (PLD). It is observed that the films grown on GGG(111) substrate exhibit perpendicular magnetic anisotropy (PMA) as compared to films grown on GGG(100) substrate. The developed PMA is confirmed from magneto-optical Kerr effect, bulk magnetization and ferromagnetic resonance measurements. Further, the magnetic bubble domains are observed in the films exhibiting PMA. The observations are explained in terms of the growth direction of Ce:YIG films and the interplay of various magnetic anisotropy terms. The observed PMA is found to be tunable with thickness of the film and a remarkable temperature stability of the PMA is observed in all the studied films of Ce:YIG deposited on GGG(111) substrate.Comment: 7 pages, 10 figure

Observation of Kondo behavior in the single crystals of Mn-doped Bi2Se3 topological insulator

The Bi2Se3 and Mn doped Bi2Se3 (i.e. Bi1.5Mn0.5Se3, referred as BiMnSe) single crystals were grown using a melt growth method and characterized for their structural, electrical and magnetic properties. These crystals were found to be of single phase having rhombohedral structure with the space group (R3¯m). The magnetoresistance measurements have been carried out in the temperature range 5-50 K, under magnetic fields up to 8 T. The variation of resistivity with temperature shows the Metallic behavior in case of Bi2Se3, and up-turn at low temperatures in the BiMnSe. Metallic behavior was observed up to T > 40 K, whereas below 40K, Kondo effect has been observed. A saturating resistance upturn at low temperatures is observed in the BiMnSe, indicating the presence of Kondo effect due to the existence of localized impurity spins. While the Bi2Se3 is diamagnetic, the BiMnSe is in ferromagnetic state at 5 K. This study opens up a new direction to investigate the physics and device applications of magnetically tunable topological insulators