Coexistence of paramagnetic-charge-ordered and ferromagnetic-metallic phases in La0.5Ca0.5MnO3 evidenced by electron spin resonance

Abstract

Abstract. Throughout a complete Electron Spin Resonance (ESR) and magnetization study of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated state established in this compound below T∼210 K. Between TN≤T≤TC, the ESR spectra shows two lines characteristic of two different magnetic phases. From the resonance field (Hr) derived for each line we argue that the incommensurate-charge-ordering phase (ICO) which coexists with ferromagnetic-metallic (FMM) clusters in this temperature interval, is mainly paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a relatively small field, which suggests that the internal energy associated with those phases is very similar. Below TN, there is an appreciable FM contribution to the magnetization and the ESR spectra indicates the presence of FM clusters in an antiferromagnetic matrix (canted). Our results show that ESR could be a very useful tool to investigate the nature of the phase-separated state now believed to play a fundamental role in the physics of mixed valent manganites.

Control of the charge-ordering-insulating phase in epitaxial La1−xCaxMnO3 (x=0.30–0.45) thin films under the anisotropic strain

“…For the 24 nm film, the PM-FM transition around 260 K can also be observed clearly, consistent with the bulk samples, 23 and with decreasing temperature the FM signal shifts to lower fields, indicating a dominant FMM state at lower temperatures. In contrast, the 20 nm film performs in a totally different way below 260 K. Instead of the sharp PM-FM transition as observed for the 24 nm film, the sample at 20 nm gives several signals from 260 to 110 K. According to previous ESR studies on PS in manganites, 24 the complex may arise from the FM, PM, and antiferromagnetic ͑AFM͒ components in the film, and the AFM signal moves to higher fields and becomes more inten- sive at still lower temperatures. Although it cannot be clearly indexed at this moment, considering the -T behaviors, the ESR spectra could be a signature of spin relaxation induced by the phase coexistence and competition in the films.…”

Griffiths phase and magnetic polaronic behavior in B-site disordering manganites

“…Such a signal distortion is extensively observed in other perovskite manganites and is attributed to the existence of FM clusters embedded in the PM matrix. 32,33 As we know, in the study of ESR spectra, the peak-to-peak width ⌬H p.p. directly reflects the interaction of spins with their environment.…”

Hexagonal CoO nanoparticles as studied by electron spin resonance

“…10 Using the approach, there is much understanding on the magnetic phases (i.e., paramagnetic, ferromagnetic, and antiferromagnetic) of diluted magnetic semiconductors. [11][12][13][14][15] In monoxide AF systems, the peculiarities of magnetic structure and the configuration of magnetic ordering of NiO and MnO nanoparticles were investigated by magnetic resonance 16 and ESR spectrometry. [17][18][19][20] To our knowledge, there are several factors that influence the appearance of ESR signals of AF nanoparticles: (i) size effect that substantially lowers the N eel point, 4,21-23 (ii) extraneous ferromagnetic impurities produced during sample fabrication, 24 (iii) the presence of uncompensated surface spins, 25 (iv) the creation of a spin-glass structure, 26 and (v) the formation of a weak magnetic moment caused by the canting of magnetic sublattices.…”