Comparison of dielectric and optical responses of chevron ferroelectric liquid crystals

Abstract

An analysis of consistency of dielectric and optical response methods is carried out for surface stabilized ferroelectric liquid crystals (SSFLC) with chevron geometry. The consistency is found both theoretically and experimentally for weak external electric fields of intermediate frequencies, for which the response of SSFLC is dominated by collective relaxation processes due to azimuthal reorientation of molecules arranging chevron layers. The methods are experimentally shown to lack consistency within very low, relatively low, and high field-frequency ranges. The disagreement appearing at relatively low frequencies is argued to be a consequence of different recording by dielectric and optical techniques the dynamics of zig-zag walls, forming defects in chevron structure.

Relaxation-to-creep transition of domain-wall motion in a two-dimensional random-field Ising model with an ac driving field

“…A perfect semicircle for the relaxation state is observed at T = 0, consistent with Eq. ( 7) and recent experiments [5,7,18]. As T increases, the creep motion gradually dominates and a linear function is observed at T = 0.2 with a slope 0.76 (3).…”

“…Although the stationary states for a dc driving field are now understood, theoretical results for the dynamic states in an ac(oscillating) driving field, H = H 0 exp(i2πf t) is limited. At low temperatures, four dynamic states (relaxation, creep, sliding and switching) may be classified in the so-called Cole-Cole diagrams [5,7,17,18]. Segmental domain-wall relaxation without net wall motion occurs at high frequencies and weak driving fields [5,7,[19][20][21].…”

“…Theory suggested that a dynamic transition might separate the relaxation and creep states [13], and very recent, experimental evidence was found in ultrathin ferromagnetic and ferroelectric films, as well as in liquid crystals [5,7,18]. Theoretically, a Debye law and a power law may describe the complex susceptibility in the relaxation and creep states respectively [7,19,25,26].…”

“…In the creep regime, i.e., f < f 2 , the domain wall creeps macroscopically, the amplitude A shows a linear behavior A(T ) ≈ aT + b at low temperatures, and the phase shift tan δ has a power law dependence on 1/f . In the literatures, the average magnetization M = (ω/2π) M (t)dt is often referred as the dynamic order parameter [7,22], and the area of the magnetization hysteresis loop S = (ω/2π) M (H)dH is also concerned [18]. By the definitions, S ∼ χ ′′ can be deduced, while M and A show similar dynamic behaviors.…”

Dynamic effect of overhangs and islands at the depinning transition in two-dimensional magnets

“…At low, but non-zero, temperatures, the sharp depinning transition is softened and a thermally activated creep state appears [21,22]. For an ac (alternative current) driving field, H(t) = H 0 exp(i2πf t), and at a nonzero temperature, the domain-wall motion exhibits different states and dynamic phase transitions, which can be classified in the so-called Cole-Cole diagrams [23][24][25].…”