CHINESE JOURNAL OF PHYSICS VOL. 39, NO. 3 JUNE 2001

Complex Magnetic Behaviors and Evidence of Magnetic Fluctuations
in Bilayered La_2-2xSr_1+2xMn₂O₇

S. Y. Wu¹, W.-H. Li¹, K. C. Lee¹, and H. D. Yang<sup>2

1</sup>Department of Physics, National Central University, Chung-Li, Taiwan 320, R.O.C.

²Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan 804, R.O.C.
(Received November 29, 2000)

Neutron diffraction, ac magnetic susceptibility, and dc electric resistivity measurements were performed to study the structural, magnetic, and electric properties of naturally bilayered La_2-2xSr_1+2xMn₂O₇, with $x=\text{0.3}$, 0.4, and 0.5. The ordering temperature of the Mn spins shifted to a higher temperature as the doping concentration was increased. Both ferromagnetic and antiferromagnetic correlations were evident. The predominant interaction in the $x=\text{0.3}$ and 0.4 compounds was ferromagnetic, whereas it was antiferromagnetic in the $x=\text{0.5}$ compound. Both the in-phase and out-of-phase susceptibilities showed complex patterns, indicating that the systems were magnetically very active. An external field as weak as 100 Oe strongly altered the susceptibility patterns. Magnetic fluctuations were evident at all temperatures studied. A structural change, which we believe to be induced by the charge ordering, occurred at around 220 K.

PACS. 61.12.-q - Neutron diffraction and scattering.
PACS. 75.30.Kz - Magnetic phase boundaries.

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