Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li_{3}N.

The magnetic properties of dilute Li_{2}(Li_{1-x}Fe_{x})N with x∼0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla reveals exceptionally sharp tunneling resonances. Li_{2}(Li_{1-x}Fe_{x})N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.

SEOM clinical guideline in nasopharynx cancer (2017).

Nasopharyngeal carcinoma (NPC) is distinct from other cancers of the head and neck in biology, epidemiology, histology, natural history, and response to treatment. Radiation therapy is an essential component of curative-intent of non-disseminated disease and the association of chemotherapy improves the rates of survival. In the case of metastatic disease stages, treatment requires platinum/gemcitabine-based chemotherapy and patients may achieve a long survival time.

SEOM clinical guidelines for the treatment of nasopharyngeal carcinoma 2013.

Nasopharyngeal carcinoma cases are not frequently encountered in our environment. Local stages are treated with radiotherapy. For advanced local stages, the association of chemotherapy with radiotherapy improves the rates of survival. In the case of metastatic disease stages, treatment requires platinum-based chemotherapy and patients may achieve a long survival time.

SEOM clinical guidelines for the treatment of head and neck cancer (HNC) 2013.

Head and neck cancer represents 5 % of oncologic cases in adults. Early stage treatments are local with surgery and/or radiotherapy. For locally advanced stages, treatment requires radiotherapy combined with platinum-based drugs or cetuximab. Induction chemotherapy should be considered for selected cases. In the case of metastatic disease, adjuvant or palliative treatment is based on platinum agents and cetuximab.

Asymmetric Berry-phase interference patterns in a single-molecule magnet.

A Mn(4) single-molecule magnet displays asymmetric Berry-phase interference patterns in the transverse-field (H(T)) dependence of the magnetization tunneling probability when a longitudinal field (H(L)) is present, contrary to symmetric patterns observed for H(L)=0. Reversal of H(L) results in a reflection of the transverse-field asymmetry about H(T)=0, as expected on the basis of the time-reversal invariance of the spin-orbit Hamiltonian which is responsible for the tunneling oscillations. A fascinating motion of Berry-phase minima within the transverse-field magnitude-direction phase space results from a competition between noncollinear magnetoanisotropy tensors at the two distinct Mn sites.

Manifestation of spin selection rules on the quantum tunneling of magnetization in a single-molecule magnet.

We present low temperature magnetometry measurements on a new Mn3 single-molecule magnet in which the quantum tunneling of magnetization (QTM) displays clear evidence for quantum mechanical selection rules. A QTM resonance appearing only at high temperatures demonstrates tunneling between excited states with spin projections differing by a multiple of three. This is dictated by the C3 molecular symmetry, which forbids pure tunneling from the lowest metastable state. Transverse field resonances are understood by correctly orienting the Jahn-Teller axes of the individual manganese ions and including transverse dipolar fields. These factors are likely to be important for QTM in all single-molecule magnets.

On-chip integration of high-frequency electron paramagnetic resonance spectroscopy and Hall-effect magnetometry.

A sensor that integrates high-sensitivity micro-Hall effect magnetometry and high-frequency electron paramagnetic resonance spectroscopy capabilities on a single semiconductor chip is presented. The Hall-effect magnetometer (HEM) was fabricated from a two-dimensional electron gas GaAsAlGaAs heterostructure in the form of a cross, with a 50 x 50 microm2 sensing area. A high-frequency microstrip resonator is coupled with two small gaps to a transmission line with a 50 Omega impedance. Different resonator lengths are used to obtain quasi-TEM fundamental resonant modes in the frequency range 10-30 GHz. The resonator is positioned on top of the active area of the HEM, where the magnetic field of the fundamental mode is largest, thus optimizing the conversion of microwave power into magnetic field at the sample position. The two gaps coupling the resonator and transmission lines are engineered differently--the gap to the microwave source is designed to optimize the loaded quality factor of the resonator (Q

High-frequency microstrip cross resonators for circular polarization electron paramagnetic resonance spectroscopy.

In this article we discuss the design and implementation of a novel microstrip resonator which allows absolute control of the microwaves polarization degree for frequencies up to 30 GHz. The sensor is composed of two half-wavelength microstrip line resonators, designed to match the 50 Omega impedance of the lines on a high dielectric constant GaAs substrate. The line resonators cross each other perpendicularly through their centers, forming a cross. Microstrip feed lines are coupled through small gaps to three arms of the cross to connect the resonator to the excitation ports. The control of the relative magnitude and phase between the two microwave stimuli at the input ports of each line allows for tuning the degree and type of polarization of the microwave excitation at the center of the cross resonator. The third (output) port is used to measure the transmitted signal, which is crucial to work at low temperatures, where reflections along lengthy coaxial lines mask the signal reflected by the resonator. Electron paramagnetic resonance spectra recorded at low temperature in an S=5/2 molecular magnet system show that 82% fidelity circular polarization of the microwaves is achieved over the central area of the resonator.

Targeting receptor tyrosine kinases and their signal transduction routes in head and neck cancer.

Squamous cell carcinoma of the head and neck (SCCHN) is the sixth most common cancer in the world. At present several therapeutic approaches, including surgical removal, chemotherapy and radiotherapy, are used. Yet a significant number of patients relapse, often with metastases. In an attempt to improve treatment of SCCHN new targeted therapies are emerging. Among them special interest has been devoted to agents that act on the epidermal growth factor receptor (EGFR) and other receptor tyrosine kinases, or the signal transduction routes used by these receptors to induce tumour cell proliferation. Such treatments include monoclonal antibodies and small molecule inhibitors of either the intracellular tyrosine kinase activity of these receptors or relevant signalling intermediates. Here we review the biological bases of these new targeted treatments, with special emphasis on the clinical results that point to an implementation of these drugs into the therapeutic armamentarium against SCCHN.

Quantum superposition of high spin states in the single molecule magnet Ni4.

Quantum tunneling of the magnetization in a single molecule magnet has been studied in experiments that combine microwave spectroscopy with high sensitivity magnetic measurements. By monitoring spin-state populations in the presence of microwave radiation, the energy splittings between low lying superpositions of high-spin states of single molecule magnet Ni4 (S=4) have been measured. Absorption linewidths give an upper bound on the rate of decoherence. Pulsed microwave experiments provide a measure of energy relaxation time, which is found to increase with frequency.

Symmetry of magnetic quantum tunneling in single molecule magnet Mn12-acetate.

The symmetry of magnetic quantum tunneling has been studied in the prototype single molecule magnet Mn12-acetate using a micro-Hall effect magnetometer and superconducting high field vector magnet system. An average crystal fourfold symmetry is shown to be due to local molecular environments of twofold symmetry that are rotated by 90 degrees with respect to one another, confirming that disorder which lowers the molecule symmetry is as important to magnetic quantum tunneling. We have studied a subset of these lower (twofold) site symmetry molecules and present evidence for a Berry phase effect consistent with a local twofold symmetry.