The accommodation field, B* , is generally defined to be the field at which the cross over from single vortex pinning to collective pinning occurs. It is determined from magnetization curves as the point where the J c plateau ends and it used as a convenient way of comparing the pinning properties of superconducting films. Similarly, the characteristic field, B c, can be obtained from magneto-optical (MO) images from when the flux fronts meet in the middle of the film. The matching field, B phi, at which there is one vortex line per pinning site, is sometimes thought to be the same as B*, but in BaZrO3-doped YBa2Cu3O7 films the calculated B phi is much higher than the observed B*. B phi can be determined from angular dependent transport measurements. All of the field values correspond to some special case in the flux pinning in the film and relate to J c. In this work we have determined B c, B* and B phi for different kinds of YBCO films using MO, magnetization and transport measurements to reveal the deeper meaning of the special fields.
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