We present 139La NMR experiments on five powder samples of lanthanum manganites, with a Mn4+ concentration ranging from the antiferromagnetic-insulator (AFM) to the ferromagnetic-conducting (FM) region of the phase diagram. We measure a positive hyperfine coupling C=0.13 T/μB. A signal from nuclei in a FM environment is present at all compositions, as evidenced by a hyperfine frequency in zero-field experiments, by a positive hyperfine shift in NMR experiments below Tc, and by a paramagnetic frequency shift following Curie-Weiss law. A signal from nuclei in an AFM environment is identified by a similar negative intercept Curie-Weiss law. The NMR spectra reveal a large temperature dependent fraction of static spin defects below Tc in the FM domains. Nuclear relaxation indicates that the FM regions are influenced by diffusing, AFM-correlated excitations, while the AFM regions probe spin fluctuations from diffusing, FM correlated excitations. These results are interpreted in terms of electronic inhomogeneities due to the presence of a magnetic small polaron.

139La NMR in lanthanum manganites: indication of the presence of magnetic polarons from spectra and nuclear relaxations / Allodi, Giuseppe; DE RENZI, Roberto; Guidi, G.. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - 57:(1998), pp. 1024-1034. [10.1103/PhysRevB.57.1024]

139La NMR in lanthanum manganites: indication of the presence of magnetic polarons from spectra and nuclear relaxations

ALLODI, Giuseppe;DE RENZI, Roberto;
1998-01-01

Abstract

We present 139La NMR experiments on five powder samples of lanthanum manganites, with a Mn4+ concentration ranging from the antiferromagnetic-insulator (AFM) to the ferromagnetic-conducting (FM) region of the phase diagram. We measure a positive hyperfine coupling C=0.13 T/μB. A signal from nuclei in a FM environment is present at all compositions, as evidenced by a hyperfine frequency in zero-field experiments, by a positive hyperfine shift in NMR experiments below Tc, and by a paramagnetic frequency shift following Curie-Weiss law. A signal from nuclei in an AFM environment is identified by a similar negative intercept Curie-Weiss law. The NMR spectra reveal a large temperature dependent fraction of static spin defects below Tc in the FM domains. Nuclear relaxation indicates that the FM regions are influenced by diffusing, AFM-correlated excitations, while the AFM regions probe spin fluctuations from diffusing, FM correlated excitations. These results are interpreted in terms of electronic inhomogeneities due to the presence of a magnetic small polaron.
1998
139La NMR in lanthanum manganites: indication of the presence of magnetic polarons from spectra and nuclear relaxations / Allodi, Giuseppe; DE RENZI, Roberto; Guidi, G.. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - 57:(1998), pp. 1024-1034. [10.1103/PhysRevB.57.1024]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11381/1632579
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