Magnetic dilution and steric effects in the multiferroic delafossite CuCrO2

Abstract

In order to get to the bottom of substitution effects reported in CuCrO 2 delafossite, structural, magnetic, and electric properties of several CuCr 1−x M x O 2 series, where M 3+ is a S = 0 cation (M 3+ = Al 3+ , Ga 3+ , Sc 3+ , Rh 3+ ), have been investigated. It is shown that the homogeneity of the substitution is element dependent and is particularly difficult to achieve for the smallest Al 3+ cation. Ferroelectricity and dielectric properties are found to depend on the x value, but also on the nature of M: The largest substitution effects are observed for the larger elements, owing to the decrease of the Cr 3+ -Cr 3+ interaction resulting from the enlargement of the in-plane lattice parameter. However, the magnetic structures of CuCr 0.9 Ga 0.1 O 2 and CuCr 0.9 Rh 0.1 O 2 , revealed close to that of CuCrO 2 by neutron diffraction, demonstrate the great stability of this antiferromagnetic incommensurate structure against the presence of {M 3+ , S = 0} cations. This emphasizes the very different nature of the magnetic ground state of CuCrO 2 , as compared to CuFeO 2 , despite their common structural characteristics.

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

“…Such an increase in M B leads to a decrease in |θ CW |, as shown in Fig. 14, which displays very good agreement with the experimental observations [45]. It is worth noting that for x = 0.3, the M B behavior is still far from that of the ideal paramagnet ( Fig.…”

“…On the other hand, it was shown that Ga 3+ directly affects the antiferromagnetic nature of the compound, leading to the possibility of a spin glass behavior [46]. Moreover, neutron powder diffraction experiments performed on CuCr 0.9 Ga 0.1 O 2 showed that the magnetic peaks observed at 1.8 K correspond to a propagation vector q = (0.329, 0.329, 0) where they are significantly broadened compared to that of CuCrO 2 , which evidences a disorder in the magnetic configuration [45]. Nevertheless, magnetoelectric properties of CuCr 1−x Ga x O 2 are still rarely studied, and therefore, complementary investigations are necessary for better understanding of these materials.…”

“…It was also shown that doping CuCrO 2 by Ga 3+ in the Cr 3+ sites results in a material that may combine the good characteristics from both semiconductors CuCrO 2 and CuGaO 2 [43,44]. This case of Ga 3+ doping is very crucial because it allows studying the effect of magnetic dilution in CuCr 1−x Ga x O 2 without a steric effect [45] due to the very close ionic radii of Cr 3+ (r Cr 3+ = 61.5 pm) and Ga 3+ (r Ga 3+ = 62 pm). Indeed, no significant change in the structural parameters of the unit cell of CuCrO 2 has been detected [45].…”

“…This case of Ga 3+ doping is very crucial because it allows studying the effect of magnetic dilution in CuCr 1−x Ga x O 2 without a steric effect [45] due to the very close ionic radii of Cr 3+ (r Cr 3+ = 61.5 pm) and Ga 3+ (r Ga 3+ = 62 pm). Indeed, no significant change in the structural parameters of the unit cell of CuCrO 2 has been detected [45]. On the other hand, it was shown that Ga 3+ directly affects the antiferromagnetic nature of the compound, leading to the possibility of a spin glass behavior [46].…”

Unconventional aspects of electronic transport in delafossite oxides

“…According to neutron powder diffraction data, magnetic susceptibility measurements, electrical permittivity and electrical polarization data of magnetically diluted CuCr 1−x M x O 2 with M = Al, Ga, Sc, Rh by Pachoud et al the magnetic ground state turned out to be very robust against removal of Cr [95]. These authors thus concluded that the magnetic ground state of CuCrO 2 is very different from that of CuFeO 2 .…”