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Samples of YBa2Cu3O7??, having about 30%?Y2BaCuO5, were prepared with a melt-process method by adding B2O3 up to 0.5?wt% to the oxides. The structural and superconducting properties of the samples were studied by x-ray diffraction, x-ray fluorescence, scanning electron microscope, magnetization and magneto-optic techniques. B2O3 additions during the melt-processing enlarge intergrain regions that weaken the conduction links between the grains. Tc drops by 1.0?6.0?K, and at 50?K Jc decreases from about 1.6 ? 104 to 1.8 ? 103?A?cm?2 with B2O3 additions up to 0.5?wt%. A?secondary peak was observed in the Jc versus field plot of the boron-free sample that decreases with boron additions. At 50?K the intragrain Jc values of the boron-free sample were about 12% higher than the intergrain Jc value, and such differences increase with B2O3 additions. These observations, together with the enlargements of the intergrain regions with B2O3 additions, suggest that most of the boron atoms take part and reside at grain boundaries.

Using a magneto-optic technique, we have studied field penetration in a sample consisting of several YBCO single crystals merged together on their basal plane. The bending of field stream lines around crystal edges in such a geometry creates an orientation of the local applied field that is nearly perpendicular to the sample surface and thus results in an almost surface-barrier-free field penetration. The penetration field was measured under conditions of a fully developed and a reduced surface barrier, and the values obtained were compared in these two cases. The results obtained show that the surface barrier causes a substantial delay of field penetration in YBCO single crystals over the whole temperature range.

This paper presents the optimal conditions for the design of a single-rod fluxgate magnetometer using Co-based amorphous magnetic wires with reduced geometrical dimensions of 100 μm in diameter. In order to enhance the performance of the current sensor (i.e. the noise level, the sensitivity, the dynamical range, the scaling factor, etc), the core materials were subjected to annealing at different annealing temperatures in a longitudinal magnetic field ranging from 0 to 0.5 T. The B–H measurements have shown that the heat treatments significantly change the magnetic parameters of the cores (the saturation field, the initial and apparent permeabilities). For instance, the initial permeability μ i attains values of between 3500 and 4700 depending on the treatment conditions. These magnetic parameters were subsequently correlated with the sensor performance by using the principles of the fluxgate physics. Consequently, the enhanced fluxgate effect with improved sensing characteristics has been obtained by annealing the wire core at 250 °C (B = 0 T). It is shown that this magnetic wire with a sensing area of 0.00785 mm2 is suitable as a sensor core for the nondestructive testing of metallic objects and the surfaces of magnetic cards. The sensor signal shows perfect linear dependence to dc or low frequency fields up to ~1 Oe. The fitting parameters R 2 of 0.9998 could be achieved in a dc field interval of −1.0 Oe and 1.0 Oe (when R 2 =1.0, all points lie exactly on the curve with no scatter). Such linearity has not been seen in such a large dynamical range until now in the rod-type single-core fluxgates. It is also shown that there is no hysteresis on the V 2f –H dc graphs (the V 2f is the sensor signal) even after applying fields as high as 100 Oe. Besides, the cross-field effect is almost zero due to the geometry of the long-thin wire.

We analyse here the sensing performance of a magnetometer which is based on the linear dc-field dependence of the second harmonic signal generated by high-T-c polycrystalline superconductors. Experiments realized in a series of polycrystalline REBa2Cu3O7-delta (RE = Y, Sm and Nd) superconductors have shown that some parameters (e.g. H-c1J and H*) peculiar to the studied superconductors change depending on the RE ions, and those determine the sensitivity limit of the magnetometer. The lowest measurable magnetic fields are 0.1, 5 and 38 nT for RE = Sm, Y and Nd, respectively at the functioning temperature of 77 K. With an upper limit above the Earth's field the magnetometer has attracted the attention of manufacturers in the industry.

We investigate the effects of B2O3 addition on structural and magnetic properties of hard magnetic BaFe12O19 particles. The conventional solid state reaction method is used as the synthesis route. Single phase BaFe12O19 could be synthesized with very small amounts of B2O3 addition and with calcination at low temperatures (850? C) in short times (1 h). B2O3 addition also improves the magnetic parameters significantly. Remanence magnetization and specific magnetization at 1.5 T increase by ~40% in magnitude although no significant variations on coercivity is observed.