Influence of La Doping on the Magnetic Properties of the Two-Dimensional Spin-Gapped System SrCu₂(BO₃)₂

Doping of the two-dimensional dimer antiferromagnet SrCu₂(BO₃)₂ has long been proposed as a potential route toward realizing resonating valence bond superconductivity in this system; however, experimental progress has remained limited. This study explores the effects of La doping on the ground state of SrCu₂(BO₃)₂ and reports the first flux growth of Sr_1-xLa_xCu₂(BO₃)₂ single crystals with nominal doping levels up to x = 0.15. Powder X-ray diffraction and energy-dispersive X-ray spectroscopy confirm the successful incorporation of La on the Sr sites within the same tetragonal I$\overline{4}$2m structure, although the effective doping was found to be <50% of the nominal concentration. La doping induces systematic changes in the magnetic properties of SrCu₂(BO₃)₂, with a reduction of the effective spin gap from 28.2 K for the undoped sample to 20.3 K for x = 0.15, as determined from the low-temperature magnetic susceptibility. The X-band electron spin resonance measurements reveal the emergence of unpaired Cu²⁺ spins, which develop antiferromagnetic correlations below ∼5.5 K. These findings corroborate the breaking of the local spin dimers in SrCu₂(BO₃)₂ induced by La doping. No superconductivity is observed across the entire doping range studied.