We present evidence of coexistence of electron paramagnetic resonance signal and anti-ferromagnetic resonance signals above the antiferromagnetic (AFM) transition (TN ) in P r0.5Ca0.5M nO3. We identify the latter with AFM rare regions within the 'Griffiths-like' phase scenario with the associated temperature scale T * extending above room temperature.
We discuss the particle size driven tunability of the coexistence of ferromagnetism and ferroelectricity in Pr0.67Ca0.33MnO3 (PCMO) with the help of x-ray diffraction (XRD), magnetization, impedance spectroscopy and remanent polarization measurements. The remanent polarization measurements using 'Positive Up Negative Down' (PUND) method clearly prove the existence of ferroelectricity in PCMO with phase separation between Zener Polaron (ZP) ordered P21nm and disordered Pbnm structures. We also find that the ferroelectric response is enhanced in nanocrystalline samples so long as ZP ordering is not destroyed while the long range antiferromagnetic ordering at low temperature in bulk system is replaced by ferromagnetic correlations in nanoparticles. The conclusion, that by reducing the crystallite size, it might be possible to make ferromagnetism and ferroelectricity coexist near room temperature, should be generally applicable to all ZP ordered manganites. [Published: Phys. Rev. B 90, 245126 (2014)]
The short ranged magnetic correlations and dynamics of hole doped Pr1–xCaxMnO3 (0.33 < x < 0.5) of different crystallite sizes have been investigated using electron spin resonance spectroscopy. The major contribution to the temperature dependence of paramagnetic line-width is attributed to the spin-lattice relaxation dominated by thermally activated hopping of small polarons with the typical activation energy of 20–50 meV. Irrespective of the crystallite size and dopant concentration, the transverse spin relaxation time (t2) follows a universal scaling behaviour of the type t2∼(T/T0)n in the paramagnetic regime, where T0 and n are the scaling parameters. Using the temperature dependence of t2, we construct a phase diagram which shows that near half-doping, the magnetic correlations associated with charge ordering not only survives even down to the crystallite size of 22 nm but is also actually enhanced. We conclude that the eventual suppression of charge ordering with reduction in the particle size is possibly more to do with the greater influence of chemical disorder than any intrinsic effect.
Pure SrTiO 3 in bulk form is known to be an 'incipient ferroelectric' where quantum fluctuations of lattice positions prevent long range ferroelectric ordering at finite temperature. We show evidence and identify the origin of ferroelectric relaxation up to nearly room temperature in single crystalline SrT iO 3 . Strikingly, the origin of the observed ferroelectric switching is intrinsic that is coherent switching of surface nanopolar regions and not due to the nucleation and growth of domains, as described by Kolmogorov-Avrami-Ishibashi (KAI) Model.
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