Angular dependence of vortex states in Sr₂RuO₄

We studied angular dependence of vortex states in Sr₂RuO₄ single crystals through magnetization measurements using micro-Hall probe. In a pristine sample, the width of magnetization hysteresis loop decreases strongly when the field is applied at large angle from the c-axis. Through angular dependence of the upper critical field, the in-plane anisotropy is estimated. In heavy-ion irradiated samples, the critical current density shows remarkable increase in a limited angle range, suggesting the presence of enhanced pinning due to introduction of columnar defects. In all samples, irreversible magnetization shows dip structures close to zero field. We discuss this dip structure in relation with the presence of time-reversal symmetry-breaking domains.