Antiferromagnetism at the YBa2Cu3O7 / La2/3Ca1/3MnO3 interface

The magnetic properties of a series of YBa2Cu3O7-x/La2/3Ca1/3MnO3 (YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures (3.5 mbar) show the expected ferromagnetic behaviour. However, field cooled hysteresis loops at low temperature show the unexpected existence of exchange bias, effect associated with the existence of ferromagnetic/antiferromagnetic (F/AF) interfaces. The blocking temperature (TB) is found thickness dependent and the exchange bias field (HEB) is found inversely proportional to the FM layer thickness, as expected. The presence of an AF material is probably associated to interface disorder and Mn valence shift towards Mn4+.Comment: 12 pages, 2 figures, 1 table, submitted to Applied Physics Letter

Influence of ion implantation on the magnetic and transport properties of manganite films

We have used oxygen ions irradiation to generate controlled structural disorder in thin manganite films. Conductive atomic force microscopy CAFM), transport and magnetic measurements were performed to analyze the influence of the implantation process in the physical properties of the films. CAFM images show regions with different conductivity values, probably due to the random distribution of point defect or inhomogeneous changes of the local Mn3+/4+ ratio to reduce lattice strains of the irradiated areas. The transport and magnetic properties of these systems are interpreted in this context. Metal-insulator transition can be described in the frame of a percolative model. Disorder increases the distance between conducting regions, lowering the observed TMI. Point defect disorder increases localization of the carriers due to increased disorder and locally enhanced strain field. Remarkably, even with the inhomogeneous nature of the samples, no sign of low field magnetoresistance was found. Point defect disorder decreases the system magnetization but doesn t seem to change the magnetic transition temperature. As a consequence, an important decoupling between the magnetic and the metal-insulator transition is found for ion irradiated films as opposed to the classical double exchange model scenario.Comment: 27 pages, 11 Figure

Large magnetic penetration depth and thermal fluctuations in a Ca10_{10}(Pt3_{3}As8_{8})[(Fe1−x_{1-x}Ptx_{x})2_{2}As2_{2}]5_{5} (x=0.097) single crystal

We have measured the temperature dependence of the absolute value of the magnetic penetration depth $\lambda(T)$ in a Ca$_{10}$(Pt$_{3}$As$_{8}$)[(Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$]$_{5}$ (x=0.097) single crystal using a low-temperature magnetic force microscope (MFM). We obtain $\lambda_{ab}$(0)$\approx$1000 nm via extrapolating the data to $T = 0$. This large $\lambda$ and pronounced anisotropy in this system are responsible for large thermal fluctuations and the presence of a liquid vortex phase in this low-temperature superconductor with critical temperature of 11 K, consistent with the interpretation of the electrical transport data. The superconducting parameters obtained from $\lambda$ and coherence length $\xi$ place this compound in the extreme type \MakeUppercase{\romannumeral 2} regime. Meissner responses (via MFM) at different locations across the sample are similar to each other, indicating good homogeneity of the superconducting state on a sub-micron scale

Inhibition of fatty acid synthase sensitizes prostate cancer cells to radiotherapy

Many common human cancers, including colon, prostate and breast cancer, express high levels of fatty acid synthase compared to normal human tissues. This elevated expression is associated with protection against apoptosis, increased metastasis and poor prognosis. Inhibitors of fatty acid synthase, such as the cerulenin synthetic analog C75, decrease prostate cancer cell proliferation, increase apoptosis and decrease tumor growth in experimental models. Although radiotherapy is widely used in the treatment of prostate cancer patients, the risk of damage to neighboring normal organs limits the radiation dose that can be delivered. In this study, we examined the potential of fatty acid synthase inhibition to sensitize prostate cancer cells to radiotherapy. The efficacy of C75 alone or in combination with X irradiation was examined in monolayers and in multicellular tumor spheroids. Treatment with C75 alone decreased clonogenic survival, an effect that was abrogated by the antioxidant. C75 treatment also delayed spheroid growth in a concentration-dependent manner. The radiosensitizing effect of C75 was indicated by combination index values between 0.65 and 0.71 and the reduced surviving fraction of clonogens, in response to 2 Gy X irradiation, from 0.51 to 0.30 and 0.11 in the presence of 25 and 35 μM C75, respectively. This increased sensitivity to radiation was reduced by the presence of the antioxidant. The C75 treatment also enhanced the spheroid growth delay induced by X irradiation in a supra-additive manner. The level of radiation-induced apoptosis in prostate cancer cells was increased further by C75, which induced cell cycle arrest in the G2/M phase, but only at a concentration greater than that required for radiosensitization. Radiation-induced G2/M blockade was not affected by C75 treatment. These results suggest the potential use of fatty acid synthase inhibition to enhance the efficacy of radiotherapy of prostate carcinoma and that C75-dependent cell cycle arrest is not responsible for its radiosensitizing effect