We applied the OFC magnetometer for studies of vortex dynamics in small-vol
ume HTS. The substitution of the solenoid coil by a flat one in a tunnel di
ode oscillator made the coil's filling factor maximal fur flat specimens cn
abling to reach 1-3 Angstrom absolute and 10(-6) relative changes of the pe
netration depth, lambda of RF magnetic field into HTS films. Oar technique
operates in high magnetic fields and measures linear changes of lambda in 1
mm range with high resolution. It is also an excellent Q-meter for detectio
n of changes similar to 10(-9)W of the absorption in HTS samples, Such abil
ities allow it to be applied in many fields of science and technology. In p
articular, detection of the magnetic field-dependent changes of the frequen
cy and amplitude of a 23MHz oscillator enabled lines on the magnetic phase
diagram for Y-Ba-Cu-O film to be constructed. It seems to have many similar
ities as compared to the diagrams defined for bulk HTS by the other methods
. However, how close is the relation in bet, may be revealed after addition
al tests on the same quality specimens.