A 139 La NMR study was carried out on melt-grown samples of La 1Ϫx Sr x MnO 3 (0рxр0.15). The microscopic magnetic structure of the parent LaMnO 3 was identified as a homogeneous antiferromagnet at low temperatures. Substituted compounds with xу0.1 demonstrate the homogeneous ferromagnetic phase. Only a lightly doped sample with xϭ0.05 shows the coexistence of NMR lines from ferromagnetic and antiferromagnetic phases. ͓S0163-1829͑99͒15901-0͔The lanthanum manganite LaMnO 3 is an antiferromagnetically correlated insulator ͑Mott insulator͒ at all temperatures. It is a parent material for a wide range of the manganites families which are so popular now. Stoichiometric LaMnO 3 below the Néel temperature T N Ϸ140 K exhibits a layerlike antiferromagnetic order; i.e., the ferromagnetically coupled spins within ac planes ͑space group P nma ͒ are antiferromagnetically coupled along b. 1 The low-temperature magnetic structure for real LaMnO 3 samples has been variously reported as spin-canted antiferromagnetic ͑AFM͒, ferromagnetic ͑FM͒, or a domain mixture of the two. This discrepancy is a result of the strong dependence of magnetic properties on the very small variations of the La/Mn ratio and of the oxygen content.Upon substitution of Sr 2ϩ for La 3ϩ , holes are induced at the Fermi level. As a result, the Mn spins first tilt until the system becomes a FM metal at high doping. The most detailed electronic and magnetic phase diagram for La 1Ϫx Sr x MnO 3 based on macroscopic magnetic and transport measurements was published in Ref. 2. It shows a canted AFM insulator for xϽ0.1, FM insulator for 0.1рx Ͻ0.17, and FM metal at xу0.2. The colossal magnetoresistance is typical for the latter part of the diagram which has attracted the main experimental ͑see Ref. 3, and references therein͒ and theoretical 4 interest. The low doping part of the phase diagram received much less attention.As to the microscopic magnetic structure ͑especially in the insulating part of the diagram͒ there has been no complete agreement until now. Recent neutron 5 and NMR ͑Refs. 6 and 7͒ studies came to very different conclusions about the doping range for coexistence of AFM and FM phases in manganites. It should be noted that the question about the real microscopic magnetic structure of this materials seems to be of principal importance in a long discussion between two theoretical models. One of the models was proposed by de Gennes 8 and predicts for undoped and lightly doped LaMnO 3 a homogeneous canted AFM phase at low temperatures. This canted structure allows us to explain the presence of FM peaks in neutron experiments. 1 The alternative model is based on the coexistence of FM and AFM phases and was proposed by Wollan and Koehler. 1 Recently the latter model was developed by Nagaev 9 who considered this phase coexistence as intrinsic feature of the material with its origin to an electronic phase separation similar to high-T c superconductors. 10 NMR of 139 La with its reasonable gyromagnetic ratio (␥ ϭ6.0146 MHz/T), moderate quadrupole moment (Qϭ0....

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