Search

In this paper, we fabricated a low-[T.sub.c] second-order superconducting quantum interference device gradiometer (SQUID) to measure magnetocardiography (MCG) in unshielded environment. The second-order gradiometer consists of the pickup coil and the SQUID. The pickup coil is formed with two single-turn coils and one double-turn coil. The three coils are connected in order of single-, double-, and single-turn coil. The coupling polarity of two single coils is opposite to the double-turn cot. The SQUID is based on double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID, a reference junction, and shunted a relaxation circuit with a resistor and an inductor. The DROS has ten times larger flux-to-voltage transfer coefficient (~ 1 mV/[[PHI].sub.o]) than that of the conventional SQUID. Therefore, DROS could be operated with a simple flux-locked loop circuit. The pickup coil and the SQUID were fabricated on the independent wafers and connected superconductively using an Nb wire. The overall size of the second-order gradiometer is 94 x 12 [mm.sup.2] with a baseline of 35 mm. The average field noise was about 8 IT/[square root of (Hz)] at 100 Hz with the second-order gradiometer in shielded or unshielded environment. The noise level is low enough to measure MCG signals in the unshielded environment. Finally, we measure the MCG in shielded and unshielded environments by using the second-order gradiometer and compared the signal characteristics measured in both environments. Index Terms--Magnetocardiography (MCG), second-order gradiometer, superconducting quantum interference device (SQUID), unshielded environment.

YBCO SQUID magnetometers for making magnetocardiograph (MCG) measurements in magnetically disturbed environments are described and discussed.

The structural and the magnetic properties of polycrystalline [La.sub.1-x] [Sr.sub.x]Co[O.sub.3] (LSCO) have been studied experimentally. The single LSCO phase in all the prepared samples were confirmed by the X-ray diffraction and X-ray photoelectron spectroscopy measurements. From the temperature dependence of inverse magnetic susceptibility, the Curie temperatures are found to be 147 K, 217 K, and 232 K for x = 0.15, 0.25, and 0.3, respectively. However, zero-field-cooled magnetization measurement reveals a spin-glass-like behavior for x = 0.15. A neutron-diffraction study does not reveal the existence of an antiferromagnetic phase at low temperatures. It is thought that a more advanced magnetic model is required to elucidate the spin-glass behavior at low Sr concentrations. Index Terms--Cluster glass (CG), [La.sub.1-x] [Sr.sub.x] Co[O.sub.3] (LSCO), neutron diffraction.

The magnetic properties of [La.sub.0.7] [Ca.sub.0.3][Mn.sub.1-x] [V.sub.x][O.sub.3] (x [less than or equal to] 0.2) perovskites have been studied. It was found that the V doping resulted in a reduction of the magnetization and a decrease of the Curie temperature. As the concentration of [Mn.sup.4+] ions is increased in the system, the antiferromagnetic component become dominant against the ferromagnetic interaction. Moreover, the coercive field above the spin-freezing transition temperature is found to follow a double exponential function. The V doping induces a decreased spin-freezing effect in [La.sub.0.7][Ca.sub.0.3]Mn[O.sub.3] due to an antiferromagnetic long-range order between V and Mn ions. Index Terms--Coercive field, colossal magnetoresistance, Curie-Weiss law, domain-wall freezing, spin freezing, vanadium.

Single layer direct-coupled YBCO SQUID magnetometers have been fabricated and characterized for the purpose of MCG measurements in magnetically disturbed environment. Two types of magnetometers have been designed and fabricated using 10 mm × 10 mm substrates. We could operate the conventional 3-mm-wide solid pickup loop magnetometers more stably than the 12-parallel-line pickup loop magnetometers in laboratory environment. We developed a first-order electronic gradiometer system with the SQUID magnetometers with axial displacement of 80 mm without any mechanical alignment of magnetometers. The system with a software filter using calculation of discrete Fourier transform could record clear magnetocardiogram in a weak magnetic shield-room. [ABSTRACT FROM AUTHOR]