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

## TL;DR

This study investigates how adding La to SrCu2(BO3)2 affects its magnetic properties, showing a reduction in the spin gap and emergence of antiferromagnetic correlations.

## Contribution

The first flux-grown single crystals of Sr1–xLa xCu2(BO3)2 with up to 15% La doping are reported, along with detailed magnetic property analysis.

## Key findings

- La doping reduces the effective spin gap from 28.2 K to 20.3 K in SrCu2(BO3)2.
- Unpaired Cu2+ spins with antiferromagnetic correlations emerge below 5.5 K due to La doping.
- No superconductivity is observed in the studied doping range.

## Abstract

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 Sr1–x
La
x
Cu2(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

4̅
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.