ABSTRACT
Two-dimensional (2D) van der Waals (vdW) ferromagnetic metals FexGeTe2 with x = 3-5 have raised significant interest in the scientific community. Fe5GeTe2 shows prospects for spintronic applications since the Curie temperature Tc has been reported near or higher than 300 K. In the present work, epitaxial Fe5-δGeTe2 (FGT) heterostructures were grown by Molecular Beam Epitaxy (MBE) on insulating crystalline substrates. The FGT films were combined with Bi2Te3 topological insulator (TI) aiming to investigate the possible beneficial effect of the TI on the magnetic properties of FGT. FGT/Bi2Te3 films were compared to FGT capped only with AlOx to prevent oxidation. SQUID and MOKE measurements revealed that the growth of Bi2Te3 TI on FGT films significantly enhances the saturation magnetization of FGT as well as the Tc well above room temperature (RT) reaching record values of 570 K. First-principles calculations predict a shift of the Fermi level and an associated enhancement of the majority spin (primarily) as well as the total density of states at the Fermi level suggesting that effective doping of FGT from Bi2Te3 could explain the enhancement of ferromagnetism in FGT. It is also predicted that strain induced stabilization of a high magnetic moment phase in FGT/Bi2Te3 could be an alternative explanation of magnetization and Tc enhancement. Ferromagnetic resonance measurements evidence an enhanced broadening in the FGT/Bi2Te3 heterostructure when compared to FGT. We obtain a large spin mixing conductance of g↑↓eff = 4.4 × 1020 m-2, which demonstrates the great potential of FGT/Bi2Te3 systems for spin-charge conversion applications at room temperature.
ABSTRACT
BACKGROUND: We have previously shown, using the chicken embryo chorioallantoic membrane (CAM) model of in vivo angiogenesis, that X-rays act on the extracellular matrix and enhance normal and tumor-induced angiogenesis. In the present work, we studied the effect of X-rays on the gene expression of three proteins that are important regulators of angiogenesis: vascular endothelial growth factor (VEGF), heparin affin regulatory peptide (HARP) and inducible nitric oxide synthase (iNOS). MATERIALS AND METHODS: An area of 1 cm2 of the CAM, restricted by a plastic ring was irradiated at room temperature. The expression of the genes was studied using RT-PCR and the amounts of the mRNAs were quantified using image analysis of the corresponding agarose gels of the RT-PCR products. RESULTS: VEGF mRNA was decreased 6 h after irradiation. However, at later time points, VEGF expression was significantly increased compared with the nonirradiated tissue. Similarly, X-rays down-regulated both HARP and iNOS expression 6 h after irradiation and the effect was reversed at later time points, similarly to the effect of X-rays on VEGF. CONCLUSION: These data support the notion that X-rays increase the expression of genes that favor angiogenesis.
Subject(s)
Carrier Proteins/genetics , Cytokines/genetics , Neovascularization, Physiologic/genetics , Neovascularization, Physiologic/radiation effects , Nitric Oxide Synthase/genetics , Vascular Endothelial Growth Factor A/genetics , X-Rays , Animals , Carrier Proteins/biosynthesis , Chick Embryo , Chorioallantoic Membrane/blood supply , Chorioallantoic Membrane/radiation effects , Cytokines/biosynthesis , Gene Expression/radiation effects , Nitric Oxide Synthase/biosynthesis , Nitric Oxide Synthase Type II , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , RNA, Messenger/radiation effects , Vascular Endothelial Growth Factor A/biosynthesisABSTRACT
X-rays have an antiangiogenic effect in the chicken embryo chorioallantoic membrane (CAM) model of in vivo angiogenesis. Our study demonstrates that X-rays induce an early apoptosis of CAM cells, modulate the synthesis and deposition of extracellular matrix (ECM) proteins involved in regulating angiogenesis and affect angiogenesis induced by tumour cells implanted onto the CAM. Apoptosis was evident within 1-2 hr, but not later than 6 hr after irradiation. Fibronectin, laminin, collagen type I, integrin alpha(v)beta3 and MMP-2 protein amounts were all decreased 6 hr after irradiation. In contrast, collagen type IV, which is restricted to basement membrane, was not affected by irradiation of the CAM. There was a similar decrease of gene expression for fibronectin, laminin, collagen type I and MMP-2, 6 hr after irradiation. The levels of mRNA for integrin alpha(v)beta3 and collagen type IV were unaffected up to 24 hr after irradiation. The decrease in both protein and mRNA levels was reversed at later time points and 48 hr after irradiation, there was a significant increase in the expression of all the genes studied. When C6 glioma tumour cells were implanted on irradiated CAMs, there was a significant increase in the angiogenesis induced by tumour cells, compared to that in non-irradiated CAMs. Therefore, although X-rays have an initial inhibitory effect on angiogenesis, their action on the ECM enhances new vessel formation induced by glioma cells implanted on the tissue.
