"Magnetic ferroelectric" has been found in a wide range of spiral magnets. However, these materials all suffer from low critical temperatures, which are usually below 40 K, due to strong spin frustration. Recently, CuO has been found to be multiferroic at much higher ordering temperature (∼ 230K). To clarify the origin of the high ordering temperature in CuO, we investigate the structural, electronic and magnetic properties of CuO via first-principles methods. We find that CuO has very special nearly commensurate spiral magnetic structure, which is stabilized via the Dzyaloshinskii-Moriya interaction. The spin frustration in CuO is relatively weak, which is one of the main reasons that the compound have high ordering temperature. We propose that high Tc magnetic ferroelectric materials can be found in double sublattices of magnetic structures similar to that of CuO. PACS numbers: 75.85.+t, Magnetic ferroelectric materials in which ferroelectricity is induced by magnetic ordering, have attracted intensive interests [1,2]. The strong magnetoelectric (ME) coupling in these materials opens up a new path to the design of multifunctional devices that allow the control of charges by the application of magnetic fields or spins by applying voltages. So far, almost all magnetic ferroelectric materials are strongly frustrated magnets [2]. Frustrated magnets have very low ordering temperatures (∼ 30 -40 K), several times smaller than the temperatures expected from their spin interaction strengths. Low critical temperature is one of the major factors that limit the applications of these important materials. Therefore a new mechanism that allows high temperature magnetic ferroelectric materials is critical.Recently, CuO was found to be multiferroic at T c =230 K, which is much higher than the critical temperatures of all other magnetic ferroelectric materials [3]. However, the mechanism for the high ordering temperature were not clear. So far, CuO is the only binary compound that has been found to be multiferroic [3]. CuO undergoes two successsive magnetic phase transitions upon cooling from room temperature to near zero temperature. Neutron scattering experiments [4] show that below T N 1 =213 K, the spin structure is collinear antiferromagnetic (AFM1) [see Fig. 1(a)]. Between T N 1 and T N 2 =230 K, the spin structure becomes non-collinear and slightly incommensurate (AFM2) [see Fig. 1(b)], with a modulation vector of Q= (0.006, 0, 0.017). Remarkably, an electric polarization of 160 µC·m −2 , which can be reversed by applying an electric field of about 55 kV/m, develops in the AFM2 phase. The electric polarization was attributed to the spiral spin structure [3,5] which was assumed to result from spin frustration and whereas the high ordering * Email address: helx@ustc.edu.cn temperature is believed to come from the strong exchange interactions [3].To clarify the mechanism behind its high ordering temperature and the origin of its ferroelectricity, we carry out first-principles studies of the multiferroism of CuO. We find ...
We investigate the phase diagrams of RMn(2)O(5) via a first-principles effective-Hamiltonian method. We are able to reproduce the most important features of the complicated magnetic and ferroelectric phase transitions. The calculated polarization as a function of temperature agrees very well with experiments. The dielectric-constant step at the commensurate-to-incommensurate magnetic phase transition is well reproduced. The microscopic mechanisms for the phase transitions are discussed.
The classic system that describes weakly activated dissociation in heterogeneous catalysis has been explained by two dynamical models that are fundamentally at odds. Whereas one model for hydrogen dissociation on platinum(111) invokes a preequilibrium and diffusion toward defects, the other is based on direct and local reaction. We resolve this dispute by quantifying site-specific reactivity using a curved platinum single-crystal surface. Reactivity is step-type dependent and varies linearly with step density. Only the model that relies on localized dissociation is consistent with our results. Our approach provides absolute, site-specific reaction cross sections.
Stepped metal surfaces are usually assumed to exhibit an increased catalytic activity for bond cleavage of small molecules over their flat single-crystal counterparts. We present experimental and theoretical data on the dissociative adsorption of molecular hydrogen on copper that contradicts this notion. We observe hydrogen molecules to be more reactive on the flat Cu(111) than on the stepped Cu(211) surface. We suggest that this exceptional behavior is due to a geometric effect, that is, that bond cleavage on the flat surface does not occur preferentially over a top site.
We present an implementation of time-dependent density functional perturbation theory for spin fluctuations, based on planewaves and pseudopotentials. We compute the dynamic spin susceptibility self-consistently by solving the time-dependent Sternheimer equation, within the adiabatic local density approximation to the exchange and correlation kernel. We demonstrate our implementation by calculating the spin susceptibility of representative elemental transition metals, namely bcc Fe, fcc Ni and bcc Cr. The calculated magnon dispersion relations of Fe and Ni are in agreement with previous work. The calculated spin susceptibility of Cr exhibits a soft-paramagnon instability, indicating the tendency of the Cr spins to condense in a incommensurate spin density wave phase, in agreement with experiment. arXiv:1707.05219v1 [cond-mat.mtrl-sci]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.