Construction of the magnetic phase diagram in small-volume HTS by an OFC magnetometer

We applied the OFC magnetometer for studies of vortex dynamics in small-volume HTS. The substitution of the solenoid coil by a flat one in a tunnel diode oscillator made the coil´s filling factor maximal for flat specimens enabling to reach 1-3 Å absolute and 10^-6 relative changes of the penetration depth, λ, of RF magnetic field into HTS films. Our technique operates in high magnetic fields and measures linear changes of λ in 1 mm range with high resolution. It is also an excellent Q-meter for detection of changes ~10^-9 W of the absorption in HTS samples. Such abilities allow it to be applied in many fields of science and technology. In particular, detection of the magnetic field-dependent changes of the frequency and amplitude of a 23 MHz oscillator enabled lines on the magnetic phase diagram for Y-Ba-Cu-O film to be constructed. It seems to have many similarities as compared to the diagrams defined for bulk HTS by other methods. However, how close the relation is in fact, may be revealed after additional tests on the same quality specimens