ABSTRACT
A magnetically, electrically or mechanically responsive material can undergo significant thermal changes near a ferroic phase transition when its order parameter is modified by the conjugate applied field. The resulting magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects are compared here in terms of history, experimental method, performance and prospective cooling applications.
Subject(s)
Iron Compounds/chemistry , Hot Temperature , Magnetic Phenomena , Phase Transition , ThermodynamicsABSTRACT
Ferroelectric hysteresis measurements on ceramic lawsonite show a temperature dependence of the remanent polarization P(r) = P(o)Θ(s)(cothΘ(s)/T - cothΘ(s)/T(c)) â¼ Q(2), Θ(s) = 26 K, where Q is the thermodynamic order parameter of the phase transition Pmcn-P 2(1)cn. This almost linear temperature evolution of P(r) proves the improper nature of ferroelectricity in lawsonite. The Curie temperature is T(c) = 124 K. The phase transition is strictly continuous, with a weak conjugated field near the transition point, and hydrogen ordering is discussed as the primary driving mechanism.
ABSTRACT
For an epitaxial Pr(0.48)Ca(0.52)MnO(3) film on NdGaO(3), we use transmission electron microscopy to observe a 'charge-ordered' superlattice along the in-plane direction a. The same film shows no electrical signatures of charge order. The in-plane electrical anisotropy ρ(a)/ρ(c) = 28 is constant, and there is no evidence of sliding charge density waves up to the large field of â¼10(3) V cm(-1).
