The improved `LC-resonator' technique (the
open-flat coil magnetometer), based on a low-power stable-frequency tunnel
diode oscillator with a single-layer open-faced coil, is very sensitive to
changes of position. About 1 Å absolute and better than 10-6 relative
resolution can be reached in distance change measurements. It is an excellent
MHz-range scientific instrument with which one may study weakly expressed fine
peculiarities of the superconductive state in small-volume thin plate-like
high-Tc superconductors (HTS). It enables changes to be detected of about
1 pH of the HTS film's magnetic inductance (changes of ~1-3 Å of
the magnetic penetration depth, λ) with very high (~10-6)
relative resolution. Owing to the pick-up coil's flat design, relatively low
operation frequency and high relative resolution, the present method has
advantages over others. It is essential for non-destructive studies of thin
flat HTS materials (with a small signal) especially near Tc (at the
beginning of the formation of `Cooper' pairs). Mainly as the result of these advantages
a new `paramagnetic' peculiarity of the
superconductive transition has been detected in Y-Ba-Cu-O film, which precedes
the well known `diamagnetic' ejection. A possible explanation of the observed effect
is given, and the influence of some external physical parameters on the effect is
revealed and discussed.
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