Evolution of ferromagnetic order in LaMnO3.05 single crystals:: Common origin of both pressure and self-doping effects -: art. no. 014436

The pressure effect on magnetic order and anisotropy of low-doped LaMnO3.05 single crystals with two competing ferromagnetic and antiferromagnetic insulating phases was studied by magnetization measurements. It was found that applied hydrostatic pressure leads to an increase of both Curie and Neel temperatures, with different rates: dT(C)/dP=0.8 K/kbar and dT(N)/dP=0.16 K/kbar. External pressure strongly suppresses the magnetic anisotropy, resulting in a decrease of the coercive field H-C with dH(C)/dP=-0.1 kOe/kbar. The results obtained indicate that the applied pressure both enhances ferromagnetic interactions and enlarges the volume fraction of the ferromagnetic phase. The evolution of the ferromagnetic phase was explained taking into account the reduction of the Jahn-Teller distortion with increasing pressure. Changes in ferromagnetic characteristics T-C, H-C, and spontaneous magnetization M-0 result mainly from the shortening of the long Mn-O distance in the MnO6 octahedron. Moreover, we found a similarity in dependences of those parameters on the degree of the MnO6 distortion for two different effects: hydrostatic pressure and the level of self-doping delta. Such a similarity strongly suggests that pressure-induced suppression of the Jahn-Teller distortion is responsible for the observed enhancement of ferromagnetism in the LaMnO3.05 crystals.