Magnetization-vector measurements were made on an YBCO (YBa2Cu3O7-δ) crystal rotated about its c-axis in various fixed fields at different temperatures. The pinning torque per vortex (τp) in the ab-plane is found to have a broad distribution in strength, similar to previous findings for polycrystalline samples of YBCO and BKBO (Ba0.57K0.43BiO3). Simple modeling shows that the τp distribution function rises linearly with increasing rp and then drops rapidly to zero. With increasing field at each temperature, the average τp decreases gradually after rising to a broad peak. The peak value of τp/ μ ( μ being the vortex moment) defines HP, a characteristic pinning field per vortex, and it is found to decrease with increasing temperature (T) in a distinctly two-component manner. One component of Hp falls off very rapidly as (1 - T/Tc)β with β ≈ 10, while the other component descends linearly to zero as T approaches Tc. A similar two-component behavior of Hp versus T is found in polycrystalline YBCO, whereas in polycrystalline BKBO HP decreases gradually with increasing T at all temperatures. The strongly temperature dependent Hp component in YBCO may derive from vortex pinning by oxygen vacancies, as suggested theoretically.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering