Relaxor ferroelectrics and related superglasses (original) (raw)
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Ferroic superglasses: Relaxor ferroelectrics PMN and SBN vs. CoFe superspin glass
Ferroelectrics, 2018
Random electric fields (RF) due to charge disorder are at the origin of polar nanoregions (PNR) in the cubic relaxor PbMg 1/3 Nb 2/3 O 3. They initiate Lacroix-B en e-type Cole-Cole semicircles, which achieve Cole-Davidson skew and dynamic power law criticality upon approaching superdipolar glass freezing. Below T g % 240 K percolation of PNR into microdomains is evidenced by interfacial creep and relaxation via Cole-Cole diagrams. Similar behavior occurs in uniaxial Sr 0.8 Ba 0.2 Nb 2 O 6 (T g % 301 K). In contrast, matrix isolated ferromagnetic nanoparticles in CoFe/Al 2 O 3 multilayers without RF interaction lack all of these effects except superglassy critical dynamics at T g % 46 K.
Physical Review B, 2016
Superdipolar glass properties of polar nanoregions (PNRs) in relaxor ferroelectric PbMg 1/3 Nb 2/3 O 3 (PMN) are compared to those of ferromagnetic nanoparticles (FNPs) in the superspin glass [Co 80 Fe 20 (0.9 nm)/Al 2 O 3 (3 nm)] 10. Both the dynamic critical properties at T > T g and nonergodicity phenomena at T < T g are comparable, but this does not apply to their polydispersivity at T T g. Due to the quenched random size and position distribution of the FNP, the superspin glass exhibits standard Cole-Cole broadening of the spectrum of relaxation frequencies at all temperatures. Contrastingly, the relaxation spectrum of the PNRs in PMN is subject to a crossover from Lacroix-Béné to Cole-Davidson statistics on cooling toward T g. Surprisingly, it becomes replaced by relaxation and creeplike domain-wall dynamics below T g as a consequence of volume percolation of the PNR at T g and formation of a ferroelectric microdomain state under the simultaneous control by quenched random electric fields and the softening ferroelectric F 1u lattice mode.
Field dependence of glassy freezing in a relaxor ferroelectric
Physical Review B, 2009
Multifrequency susceptibility measurements on the perovskite relaxor ferroelectric ͑PbMg 1/3 Nb 2/3 O 3 ͒ 0.88 ͑PbTiO 3 ͒ 0.12 were performed at various strengths of dc electric field applied along the ͓111͔ direction. The temperature-frequency dependences fit the Vogel-Fulcher form, allowing the extraction of a frequency-independent glassy freezing temperature. These Vogel-Fulcher temperatures showed significant reductions in applied fields, following an empirical Gabay-Toulouse form, similar to vector spin glasses. The magnitude of the sensitivity indicates that the glassy state is formed by interactions among the same entities which account for the susceptibility, i.e., the polar nanoregions. That interpretation is supported by other data showing a loss of Vogel-Fulcher behavior in a powder sample of PbMg 1/3 Nb 2/3 O 3 , with grains too small to support large-scale internanoregion cooperativity.
Surface Domain Structures and Mesoscopic Phase Transition in Relaxor Ferroelectrics
Advanced Functional Materials, 2011
Relaxor ferroelectrics are a prototypical example of ferroic systems in which interplay between atomic disorder and order parameters gives rise to emergence of unusual properties, including non-exponential relaxations, memory effects, polarization rotations, and broad spectrum of bias-and temperatureinduced phase transitions. Despite more than 40 years of extensive research following the original discovery of ferroelectric relaxors by the Smolensky group, the most basic aspect of these materials -the existence and nature of order parameter -has not been understood thoroughly. Using extensive imaging and spectroscopic studies by variable-temperature and time resolved piezoresponse force microscopy, we fi nd that the observed mesoscopic behavior is consistent with the presence of two effective order parameters describing dynamic and static parts of polarization, respectively. The static component gives rise to rich spatially ordered systems on the ∼ 100 nm length scales, and are only weakly responsive to electric fi eld. The surface of relaxors undergoes a mesoscopic symmetry breaking leading to the freezing of polarization fl uctuations and shift of corresponding transition temperature.
Phase transition in a super superspin glass
EPL (Europhysics Letters), 2013
PACS 75.50.Lk -Spin glasses and other random magnets PACS 75.10.Nr -Spin-glass and other random models PACS 75.40.Cx -Static properties Abstract -We here confirm the occurrence of spin glass phase transition and extract estimates of associated critical exponents of a highly monodisperse and densely compacted system of bare maghemite nanoparticles. This system has earlier been found to behave like an archetypal spin glass, with e.g. a sharp transition from paramagnetic to non-equilibrium behavior, suggesting that this system undergoes a spin-glass phase transition at a relatively high temperature, Tg ∼ 140 K.
A ferromagnet with a glass transition
Europhysics Letters (EPL), 2001
PACS. 05.70.Jk -Critical point phenomena. PACS. 64.70.Pf -Glass transitions. PACS. 75.10.Nr -Spin-glass and other random models.
The magnetic phase transition in amorphous ferromagnets and in spin glasses
Journal of Magnetism and Magnetic Materials, 1983
The magnetic phase transition in materials with exchange disorder (amorphous fcrromagnets. spin gla~c.\) 1s dihcubacd. In the critical temperature range the behavior of amorphous ferromagnetic transition mctalLmctalloid glasses i> found to be similar to the one derived for a three-dimensional homogeneous H&e&erg fcrromagnet. The most prominent diffcrencc between disordered and homogeneous materials is manifested in a large temperature range of dc\iations from the mean field behavior beyond the critical region, as observed experimentally for the temperature depcndcncc of the linear susceptibility of amorphous ferromagnets and of the nonlinear susceptibi!ity of spin glasses. A molecular field theory with correlations in space and time is developed, which relates the deviations from the mean field behavior to the interplay between the temperature dependent thermal correlations in the spin bystem and the spatial fluctuations of the material. Application to dynamical processes (kinetic critical slowing down) is discussed.