High-temperature & high-polarization cuprate multiferroics – HTHPCM
The HTHPCM project consists on a combined theoretical-experimental investigation of 8 series of compounds, offering a wide range of (1) topologies (perovskite, kagome and diamond lattices, edge and corner sharing CuO4 plaquettes, isolated clusters…), (2) critical temperatures TN (varying from 11 to 380K), and (3) chemistry (oxides, oxyhalides, and halides). While pure oxides and halides have been deeply investigated, very few is known for the mixed anions systems both from the theoretical and experimental sides. This project will contribute to enlarge the understanding of the mixed anion systems which is still a growing field and is of direct interest for ME-MF applications.
For each compound (task 1.1), we will first characterize the atomic structure at ambient pressure (task 1.2). These structural data will be used as starting point of the DFT geometry optimizations (task 2.1) and phonons calculations (task 2.2) that will be compared to the XRD and Raman measurements (task 1.2). Then we will estimate the magnetic parameters (task 2.3) in order to simulate the ME-MF properties (task 2.4). These thermodynamic theoretical data will be compared to the experimental ones (tasks 2.3 and 2.4). This experimental-theoretical dialog will provide an accurate understanding of the structural, magnetic and ME-MF properties at ambient pressure. We will then consider the effect of high pressure starting from the simulations, in order to orientate the experimental investigations, which require large-scale facilities experimental campaigns (proposals supported by theoretical predictions).
1) Creation of a database gathering all the magnetic cuprates with an atomic structure compatible with a three-dimensional magnetic order.
2) Structural and magnetic study under pressure of Cu3Bi(SeO3)2O2X, Cu3(TeO3)2X2 and Cu2TeO5X2 (internship M2 G. Baudesson).
3) Structural and magnetic study of BaCuF4 (M2 J. Leveque internship). This study, combining WFT, DFT and MC simulations, invalidated a previous theoretical result published in PRL, indicating a 3D magnetic temperature close to 300K (TN = 275K). Following this, a study of the magnetic properties of BaNiF4 was carried out (article accepted).
4) Taking into account the pressure and calculating the evolution of the structural, magnetic and dielectric properties of BaCuF4 (D. Vincent Thesis - article in progress).
5) Theoretical determination of the magnetic properties of CuCr2O4, NaCuF3 and CoCu2O3 by DFT & WFT calculations and MC simulations (Thesis by J. Leveque).
6) Theoretical determination of the magnetic and dielectric properties of La2Cu2O5 (D. Vincent Thesis).
7) Taking into account the pressure and calculating the evolution of the structural and magnetic properties of Cu3TeO6 (Stage L3 M. Tardieux).
8) Measurements of the evolution of the dielectric constant under pressure (up to 7GPa) for CuO. This experimental study was published in PRB in June 2021 (Phys. Rev. B 103, 214432). It is coupled with DFT and MC calculations of magnetic and multiferroic properties.
9) Raman spectroscopy measurements on CuO and WFT calculations. This study highlights a lower symmetry than that reported for CuO, which explains the appearance of electrical polarization. Phonon calculations were also performed to corroborate these theoretical results. A study of the effect of pressure on phonon modes and on Raman spectra is underway.
Since multiferroics are materials exhibiting multifunctional properties, such as the coexistence of magnetization and PS, they can be switched electrically or magnetically due to the magneto-electric coupling. If this coupling is strong enough we can imagine using them as actuators, transducers and storage devices. Other potential applications include multiple-state memory elements, in which data is stored both in the electric and magnetic states, or novel memory media, which might allow for electrical writing and non-destructive magnetic readout operation. In addition, the possibility to flip a “magnetic bit” without using a magnetic field (but an electric field) leads to a significant decrease of heat dissipation and thus a reduction of the energy consumption. So far, no promising materials, having a strong coupling between both properties and a sufficiently large voltage-induced magnetism at room temperature, has been found. We were the first team to consider high-pressure as an efficient tuning factor of the multiferroic properties, leading to a prediction of RT multiferroicity of CuO under 20-40 GPa. The international scientific community is now considering high-pressure as “an effective perturbation to achieve high-performance multiferroics”. This research activity is still quite new and challenging to handle from the experimental side (difficulty to measure dielectric properties under very high-pressure), and from the theoretical side (a multiscale approach is needed and it requires methods going beyond DFT and consideration of large systems). Our project associating the multiscale theoretical approach with experimental feedback could potentially lead to a real breakthrough with new concepts to produce room temperature efficient multiferroics. The novel consideration of uniaxial pressure which will lead to different structural, magnetic and ferroelectric properties is a bonus. This objective is fully in the scope of the ANR 2019 work program Domaine E.2 – axe 2.4 ”Matériaux métalliques et inorganiques et procédés associés” with “Propriétés fonctionnelles, Approches multi-échelles pour la caractérisation et la simulation, couplages multi-physiques”. Moreover, our state-of-the-art multiscale computational work on the treatment of the magneto-electric interactions and the non-hydrostatic pressure will highly benefit to the respective theoretical communities (DFT, MC, WFT) and pave the way towards future studies to explore further similar structure-properties relationships in parent material science fields, including mixed anions systems.
1) Detailed understanding of the magnetic properties of BaCuF4 contradicting the idea that it can be multiferroic at high temperature, regardless of the pressure applied to the compound.
2) Study of a nickel compound, BaNiF4, for which the existence of a second magnetic orbital eg simultaneously allows strong coupling and an increase in dimensionality. Our studies have shown that it is a two-dimensional system with a magnetic anisotropy allowing the existence of a long-range AFM order at finite temperature. An interesting result is the existence at low temperatures of a slight non-collinearity in the order AFM that can be described with an effective Dzyloshinsy-Moriya term whose physical origin is not the usual anisotropy of the interactions. . An article entitled “Theoretical study of the magnetic properties of BaNiF4”, has been submitted and is being revised.
3) Dielectric measurements under pressure (up to 7 GPa) of CuO confirming the stabilization of the ferroelectric phase under pressure.
4) Raman measurements and phonon calculations on CuO, known to be multiferroic. This study offers a new understanding of the emergence of ferroelectricity in this compound.
5) Theoretical determination of the magnetic couplings (J) of many cuprates. Some present strong values ??of J, compatible with a three-dimensional magnetic order and promising for the target of the project.
6) Installation of a new device allowing measurements of dielectric constant under pressure, with in-situ pressure control, and over a wide temperature range (2K-300K). This apparatus is the first of its kind in France.
Magnetoelectric (ME) multiferroics (MF), which combine electric and magnetic dipole orders, are multifunctional materials with a high potential in new technologies. It can be used to reduce computer memory energy consumption, to improve magnetic field sensors or in spintronic applications. Unfortunately, only few ME crystals are known to date, and even less could lead to industrial applications. Indeed, they usually give a small response (electric polarization, PS) and need low functioning temperature to exhibit the desired ME-MF properties.
The main goal of this project is the search of high-temperature and high-polarization cuprate multiferroics (HTHPCM), i.e. (1) with a large ME-MF coupling and thus large PS, (2) operating at room-temperature (RT), and (3) showing an electric-field magnetization reversal.
We aim at the investigation of a series of compounds (known to be ME-MF or not) having the following specifications: (1) large magnetic exchange couplings in order to reach high temperature functioning and (2) magnetic frustrations to have a strong ME-MF coupling mechanism based on exchange-striction and thus large ferroelectric polarization (Ps). Cuprates are ideal candidates for these two reasons and interestingly exhibit both types I and II ME-MFs. The present project combines advanced experimental techniques (X-ray, neutron and Raman techniques under pressure, magnetometry, dielectric measurements…) and state-of-the-art calculations (density functional theory (DFT), multireference wavefunction (WFT) calculations and Monte-Carlo (MC) simulations).
The main focus of the HTHPCM project is to tune the MF properties through both chemical and external (physical) pressures. The idea is to explore in an effective manner the potential effects of chemical pressure by applying high pressure on existing compounds either established as MF or not. We believe that such a strategy could significantly speed up the discovery of optimal building blocks for the ME-MF properties.
The HTHPCM project consists on a combined theoretical-experimental investigation of 8 series of compounds, offering a wide range of (1) topologies (perovskite, kagome and diamond lattices, edge and corner sharing CuO4 plaquettes, isolated clusters…), (2) critical temperatures TN (from 11K to 380K), and (3) chemistry (oxides, oxyhalides, and halides). While pure oxides and halides have been deeply investigated, very few is known for the mixed anions systems both from the theoretical and experimental sides. This project will contribute to enlarge the understanding of the mixed anion systems which is still a growing field and is of direct interest for ME-MF applications.
For each compound, we will first characterize the atomic structure at ambient pressure. These structural data will be used as starting point of the DFT geometry optimizations and phonons calculations that will be compared to the XRD and Raman measurements. Then we will estimate the magnetic parameters in order to simulate the ME-MF properties. These thermodynamic theoretical data will be compared to the experimental ones. This experimental-theoretical dialog will provide an accurate understanding of the structural, magnetic and ME-MF properties at ambient pressure. We will then consider the effect of high pressure starting from the simulations, in order to orientate the experimental investigations, which require large-scale facilities experimental campaigns (proposals supported by theoretical predictions).
Monsieur Xavier Rocquefelte (INSTITUT DES SCIENCES CHIMIQUES DE RENNES)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
ISCR INSTITUT DES SCIENCES CHIMIQUES DE RENNES
CINaM Centre National de la Recherche Scientifique Délégation Provence et Corse DR12
NEEL Institut Néel
PHELIQS Photonique Electronique et Ingénierie Quantiques
Help of the ANR 468,363 euros
Beginning and duration of the scientific project: December 2019 - 42 Months