Evidence for Competing Order Parameters in the Paramagnetic Phase of Layered Manganites.

Berger, A. ; Mitchell, J. F. ; Miller, D. J. ; Bader, S. D.

Technical Information Center Oak Ridge Tennessee

关键词: Layered manganites;    Paramagnetism;    Magnetic fields;    Temperatures;    Ferromagnetics;   

RP-ID  :  DE2001768583

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

The magnetic field and temperature dependence of the magnetic susceptibility and magnetization is studied for the ferromagnetic layered manganites in the composition range x = 0.32-0.40. In the paramagnetic phase, the susceptibility exhibits an anomalous maximum at an intermediate magnetic field value. The size of this field-induced susceptibility enhancement increases dramatically with x from 10% for x = 0.32 to 160% for x = 0.40. The temperature dependence of the effect shows a maximum at T approximately 1.1 Tc for all x. Quantitative analysis in terms of the Landau theory of phase transitions enables us to identify a distortion of the free energy F in the pararmagnetic phase that is associated with the susceptibility anomaly. This free energy distortion corresponds to a magnetic system that approaches a first order magnetic phase transition as the temperature is lowered towards Tc. Such a behavior is indicative of a second, competing order parameter, which is identified as the recently observed charge density wave. In the immediate vicinity of TC, the anomaly disappears and the system seems to undergo a more conventional second order paramagnetic-ferromagnetic phase transition.