Directional Vortex Pinning at Microwave Frequency in YBa2Cu3O7-x Thin Films with BaZrO3 Nanorods

We investigate the effect of the anisotropy and of the directional pinning in YBa2Cu3O7−x films grown by pulsed laser ablation from targets containing BaZrO3 at 5 mol%. BaZrO3 inclusions self-assemble to give nanorods oriented along the c-axis, thus giving a preferential direction for vortex pinning. The directionality of vortex response is studied at high ac frequency with the complex microwave response at 48 GHz, as a function of the applied field and of the angle θ between the field and the c-axis. The complex microwave response does not exhibit any angular scaling, suggesting that the structural anisotropy of YBa2Cu3O7−x is supplemented by at least another preferred orientation. The pinning parameter r shows evidence of directional pinning, effective in a wide range of angles around the c-axis (thus ascribed to BZO nanocolumns).