Stability under pressure and magnetic field of the ferromagnetic-insulating phase in lightly doped La1-xSrxMnO3 crystals

The stability of the ferromagnetic-insulating (FI) phase occurring at T<T-F I is studied in a series of La1-xSrxMnO3 (0.1 less than or equal to x less than or equal to 0.14) single crystals as function of temperature (T), pres sure (P), and magnetic field (H). It is found that for all samples, the low -temperature ferromagnetic and insulating phase is stabilized under pressur e and field, i.e., dT(FI)/dP>0 and dT(FI)/dH>0. Remarkably enough, these de rivatives have very similar values irrespective of the hole concentration. This observation is consistent with the existence of superexchange-type fer romagnetic interactions. On the other hand, it is also shown that typical s ignatures of the first-order transition occurring at T-FI disappears for hi gh doping rate (x greater than or equal to 0.14). These results are discuss ed on the basis of the recently proposed orbital ordering models.