⁵⁵Mn NMR study of the A‐type antiferromagnetic and metallic manganites La_1–xSr_xMnO₃ (0.5 ≤ x ≤ 0.6)

Abstract

The microscopic magnetic and electronic properties of La1‐xSrxMnO3 (0.5 ≤ x ≤ 0.6) were investigated using 55Mn nuclear magnetic resonance (NMR). The NMR spectral intensity showed a large decrement as x increases above the boundary (x ∼ 0.52) of ferromagnetic (FM) and A‐type antiferromagnetic (AFM) phases. The spectrum of the samples shows a coexistence of two different phases, i.e., a metallic major phase and an insulating minor phase. The spin‐spin relaxation time strongly depends on the resonance frequency, indicating that the Shul‐Nakamura process by spin‐wave excitation is the dominant relaxation mechanism. This type of frequency dependence of the spin‐spin relaxation time was not observed in the CE‐type AFM manganite Nd0.5Sr0.5MnO3. The A‐type AFM spin structure and the Shul‐Nakamura relaxation process appears to be a unique characteristics of La1‐xSrxMnO3 (0.54 ≤ x ≤ 0.6) that is related to the 2D‐like spin coupling in a nearly tetragonal crystal structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)