Effects of Zr Doping on Magnetic and Structural Properties of DyBa2Cu3O $_{7-\delta }$ Thin Films

DyBa<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>(Cu<inline-formula> <tex-math notation="LaTeX">$_{1-x}$</tex-math></inline-formula>-Zr<inline-formula><tex-math notation="LaTeX">$_x$ </tex-math></inline-formula>)<inline-formula><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> O <inline-formula><tex-math notation="LaTeX">$_{7-\delta }$</tex-math></inline-formula> thin films (with <italic>x </italic> = 0.00, 0.02, 0.04, and 0.06) were synthetized using the chemical solution deposition method on single crystalline LaAlO<inline-formula><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> substrates. Effects resulting from Zr doping were investigated by means of magnetic and structural measurements. X-ray diffraction analysis demonstrated a strong <italic>c</italic>-axis orientation in the DyBa<inline-formula> <tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>(Cu<inline-formula><tex-math notation="LaTeX">$_{1-x}$ </tex-math></inline-formula>-Zr<inline-formula><tex-math notation="LaTeX">$_x$</tex-math></inline-formula>) <inline-formula><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> O<inline-formula> <tex-math notation="LaTeX">$_{7-\delta }$</tex-math></inline-formula> thin films, with only minor reflections due to the presence of Dy<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> O<inline-formula> <tex-math notation="LaTeX">$_3$</tex-math></inline-formula> and BaZrO<inline-formula><tex-math notation="LaTeX">$_3$ </tex-math></inline-formula> phases. Narrow transitions with <inline-formula><tex-math notation="LaTeX">$\Delta$ </tex-math></inline-formula><italic>T</italic><inline-formula><tex-math notation="LaTeX">$_c$</tex-math> </inline-formula> ranging from 1 to 2 K for samples with <italic>x</italic> = 0.00 and 0.06, respectively, were observed in ac magnetic susceptibility curves, where the nondoped sample demonstrated the highest <italic>T</italic> <inline-formula><tex-math notation="LaTeX">$_c^{\text{onset}}$</tex-math></inline-formula> of 91.7 K compared to the Zr-doped samples. Critical current densities <italic>J</italic><inline-formula><tex-math notation="LaTeX">$_c$ </tex-math></inline-formula> of the thin films were obtained from magnetization loop measurements with applied magnetic fields up to 6 T and by employing the Bean model. The sampled doped with 4% Zr exhibited the highest <italic>J </italic><inline-formula><tex-math notation="LaTeX">$_c$</tex-math></inline-formula> value (<italic>J</italic> <inline-formula><tex-math notation="LaTeX">$_c$</tex-math></inline-formula> = 3.5 MA/cm<inline-formula> <tex-math notation="LaTeX">$^2$</tex-math></inline-formula>, self-field, 77 K) in the low field range and we, in general, observed that Zr-doped films demonstrated higher values compared to the pure sample. Pinning force plots ( <italic>F</italic><inline-formula><tex-math notation="LaTeX">$_p$</tex-math></inline-formula> versus <italic>B</italic> ) reveal a significant improvement over the magnetic field range investigated of the maximum pinning force for Zr-doped samples. We found <italic>F</italic><inline-formula><tex-math notation="LaTeX">$_p^{\text{Max}}$</tex-math> </inline-formula> = 1.7 GN/m<inline-formula><tex-math notation="LaTeX">$^3$</tex-math></inline-formula> and 3.8 GN/m <inline-formula><tex-math notation="LaTeX">$^3$</tex-math></inline-formula> for pure and 6% Zr samples, respectively. Analysis based on the Dew-Hughes model shows that normal surface pinning is the dominating pinning mechanism.