Effects of Ga doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 : Ab initio and Monte Carlo approaches

The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite ${\mathrm{CuCrO}}_{2}$ are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to $30%$ of ${\mathrm{Cr}}^{3+}$ ions by ${\mathrm{Ga}}^{3+}$ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that ${\mathrm{CuCr}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{O}}_{2}$ preserves its magnetoelectric properties up to $x\ensuremath{\simeq}0.15$ with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing $x$ and eventually disappears at $x\ensuremath{\ge}0.2$. Our simulations show that ${\mathrm{Ga}}^{3+}$ doping increases the Curie-Weiss temperature of ${\mathrm{CuCr}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{O}}_{2}$, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by ${\mathrm{Ga}}^{3+}$ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for $x\ensuremath{\le}0.15$ through simulating $P\text{\ensuremath{-}}E$ hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.