Magnetic and electronic properties of Eu1-xSrxMnO3 (0.3<x<0.7) single crystals

Among versatile perovskite manganites showing colossal magnetoresistance (CMR), Eu1-xSrxMnO3 around x similar to 0.4 shows the ferromagnetic metal with the lowest transition temperature (similar to 40 K) due to the narrowest one-electron bandwidth and hence is readily subject to the drastic phase changes with variations in temperature, magnetic field, and hole doping (x). We have investigated the variation in the electronic state with x with use of single crystals. As x increases, the ferromagnetic metal at 0.38 < x < 0.47 changes to a spin-glasslike insulator at 0.48 < x < 0.5, the layered antiferromagnetic (A-type) state at 0.51 < x < 0.6, and the chained antiferromagnetic (C-type) state at 0.6 < x, respectively. Due to the increased disorder upon alloying of Eu/Sr, the charge/orbital ordering with the modulation vector (0, q, 0) with q=1/2 in the orthorhombic Pbnm setting (a(0)similar to b(0)similar to c(0)/root 2 similar to root 2a(p), a(p) being the lattice parameter of the pseudocubic lattice) cannot be formed in a long range but remains short ranged. In the vicinity of x=0.5, an application of an external magnetic field removes such short-range charge/orbital ordering (q=1/2) to cause an insulator to metal transition or CMR. In a broad range of x (0.55 < x < 0.59), the critical temperature for the layered antiferromagnetic state is relatively lowered and alternatively the charge/orbital ordering with q similar to 1/3 becomes to be visible. It has also been found that the modulation is temperature dependent; commensurate with q similar to 1/3 upon the transition while incommensurate with q>1/3 at low temperatures.