Magnetic properties and the phase diagram of La1-xSrxMnO3 for x <= 0.2

We report on susceptibility, magnetization, magnetoresistance, and ultrason ic studies of La1-xSrxMnO3 for x less than or equal to 0.2. The magnetic su sceptibilities in the different high-temperature paramagnetic phases are st udied in detail. We provide experimental evidence for the occurrence of sho rt-range ferromagnetic order within the paramagnetic phase. Furthermore, we can exclude the possibility of electronic phase separation for x < 0.1. Va riable-range-hopping conductivity dominates in the paramagnetic and magneti cally ordered phases. From the anomalies at the structural and magnetic pha se transitions, we arrive at a phase diagram which shows a ferromagnetic an d insulating ground state for 0.1 less than or equal to x less than or equa l to 0.15, followed by a canted antiferromagnetic phase at higher temperatu res. The ferromagnetic transition is strongly coupled to a structural trans ition from a Jahn-Teller-distorted phase to a pseudocubic orthorhombic phas e and is accompanied by the appearance of large positive magnetoresistance effects. We interpret the rich phase diagram close to x = 1/8 in terms of o rbital ordering, due to an interplay of superexehange interactions and Jahn -Teller distortions.