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Register a new userEpitaxial ferromagnetic semiconductor GdN thin films on Si substrate
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A major challenge for the next generation of spintronics devices is the implementation of ferromagnetic-semiconductor thin films as spin injectors and detectors. Spin-polarised carrier injection cannot be accomplished efficiently from metals, and coupled with the rarity of intrinsic ferromagnetic semiconductors this has driven intensive study of diluted magnetic semiconductors. Chief among these is the doped III-V compound (Ga,Mn)As. These materials suffer from a number of drawbacks; they (i) require magnetic-ion doping well above the solubility limit, and (ii) must be hole doped to above the degenerate limit, preventing independent control of the carrier concentration and charge sign. Here we demonstrate the first epitaxial growth of a recently-characterised intrinsic ferromagnetic semiconductor, GdN, on silicon substrates, providing an essential step on the way to integrate new spintronics functionalities into Si-based technology. The films have been characterised as regards their growth toward fully relaxed GdN, the density and mobility of their carriers, and their magnetic behaviour.
BiFeO3 thin films with various thicknesses were grown epitaxially on (001) LaSrAlO4 single crystal substrates using pulsed laser deposition. High resolution x-ray diffraction measurements revealed that a tetragonal-like phase with c-lattice constant ~4.65 {AA} is stabilized by a large misfit strain. Besides, a rhombohedral-like phase with c-lattice constant ~3.99 {AA} was also detected at film thickness of ~50 nm and above to relieve large misfit strains. In-plane piezoelectric force microscopy studies showed clear signals and self-assembled nanoscale stripe domain structure for the tetragonal-like regions. These findings suggest a complex picture of nanoscale domain patterns in BiFeO3 thin films subjected to large compressive strains.
The correlation between magnetic and structural properties of Co_{2} FeAl (CFA) thin films of different thickness (10 nm<d< 100 nm) grown at room temperature on MgO-buffered Si/SiO2 substrates and annealed at 600lyxmathsym{textdegree}C has been studied. XRD measurements revealed an (011) out-of-plane texture growth of the films. The deduced lattice parameter increases with the film thickness. Moreover, pole figures showed no in-plane preferential growth orientation. The magneto-optical Kerr effect hysteresis loops showed the presence of a weak in-plane uniaxial anisotropy with a random easy axis direction. The coercive field measured with an applied field along the easy axis direction and the uniaxial anisotropy field increase linearly with the inverse of the CFA thickness. The microstrip line ferromagnetic resonance measurements for in-plane and perpendicular applied magnetic fields revealed that the effective magnetization and the uniaxial in-palne anisotropy field follow a linear variation versus the inverse CFA thickness. This allows deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2
Whether {alpha}double prime-Fe16N2 possesses a giant saturation magnetization (Ms) has been a daunting problem among magnetic researchers for almost 40 years, mainly due to the unshakable faith of famous Slater-Pauling (SP) curve and poor consistency on evaluating its Ms. Here we demonstrate that, using epitaxy and mis-fit strain imposed by an underlying substrate, the in-plane lattice constant of Fe16N2 thin films can be fine tuned to create favorable conditions for exceptionally large saturation magnetization. Combined study using polarized neutron reflectometry and X-ray diffraction shows that with increasing strain at the interface the Ms of these film can be changed over a broad range, from ~2.1T (non-high Ms) up to ~3.1T (high Ms). We suggest that the equilibrium in-plane lattice constant of Fe16N2 sits in the vicinity of the spin crossover point, in which a transition between low spin to high spin configuration of Fe sites can be realized with sensitive adjustment of crystal structure.
Crystal and domain structures of tensile-strained BiFeO3 films grown on orthorhombic (110)o PrScO3 substrates were investigated. All films possess a MB-type monoclinic structure with 109o stripe domains oriented along the [=i10]o direction. For films thicknesses less than ~40 nm, presence of well-ordered domains is proved by the detection of satellite peaks in synchrotron x-ray diffraction studies. For thicker films, For thicker films, only the Bragg reflections from tilted domains were detected. This is attributed to the broader domain size distribution in thicker films.Using planar electrodes,the in-plane polarization of the MB phase is determined to be 85 uC/cm2, which is much larger than that of compressive strained BiFeO3 films. Our results further reveal that the substrate monoclinic distortion plays a major role in determining the stripe domain formation of the rhombohedral ferroic epitaxial thin films, which sheds light to the understanding of elastic domain structure evolution in many other functional oxide thin films as well.
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