Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic (original) (raw)

Magnetic Structure and Ordering of Multiferroic Hexagonal LuFeO_{3}

Physical review letters, 2015

We report on the magnetic structure and ordering of hexagonal LuFeO_{3} films of variable thickness grown by molecular-beam epitaxy on YSZ (111) and Al_{2}O_{3} (0001) substrates. These crystalline films exhibit long-range structural uniformity dominated by the polar P6_{3}cm phase, which is responsible for the paraelectric to ferroelectric transition that occurs above 1000 K. Using bulk magnetometry and neutron diffraction, we find that the system orders into a ferromagnetically canted antiferromagnetic state via a single transition below 155 K regardless of film thickness, which is substantially lower than that previously reported in hexagonal LuFeO_{3} films. The symmetry of the magnetic structure in the ferroelectric state implies that this material is a strong candidate for linear magnetoelectric coupling and control of the ferromagnetic moment directly by an electric field.

Novel Approaches for Genuine Single-Phase Room Temperature Magnetoelectric Multiferroics

Key Processing and Characterization Issues, and Nanoscale Effects, 2016

With the seemingly inexorable increase in the use of devices designed to access the internet for an ever increasing series of applications, there is a constant need for data storage technologies with higher densities, non-volatility and lower power consumption. 3 Single-phase, room temperature magnetoelectric multiferroic materials are of considerable interest for such applications. 4 The unique advantage of these advanced materials is that not only could they find application in high storage density, low-power memory devices that can be electrically written and magnetically read, but also by constructing devices that exploit the presence of both ferroelectric and ferromagnetic states, memory technologies with 4-state logic could be achieved 5-representing a clear improvement over current 2-state logic memory. However, materials that are both multiferroic and magnetoelectric at room temperature are very unusual. 6 In this chapter, we review approaches currently under investigation for the fabrication of single phase magnetoelectric multiferroics, from bulk ceramics to those in thin film form. We present This is the pre-peer reviewed version of the following article which has been published in final form at

Multiferroics and magnetoelectrics: thin films and nanostructures

Journal of Physics: Condensed Matter, 2008

Multiferroic materials, or materials that simultaneously possess two or more ferroic order parameters, have returned to the forefront of materials research. Driven by the desire to achieve new functionalities-such as electrical control of ferromagnetism at room temperature-researchers have undertaken a concerted effort to identify and understand the complexities of multiferroic materials. The ability to create high quality thin film multiferroics stands as one of the single most important landmarks in this flurry of research activity. In this review we discuss the basics of multiferroics including the important order parameters and magnetoelectric coupling in materials. We then discuss in detail the growth of single phase, horizontal multilayer, and vertical heterostructure multiferroics. The review ends with a look to the future and how multiferroics can be used to create new functionalities in materials.

Structural correlation to spontaneous electric and magnetic order in multiferroic LiCr0.99Fe0.01O2

Scripta Materialia, 2014

We report the effect of Fe doping on structural, magnetic, and electric polarization in LiCr0.99Fe0.01O2. Although antiferroelectric transition remains at 62 K, Néel temperature shifts toward higher temperature to 95 K. This may indicate release of magnetic frustration in the antiferromagnetically coupled 2-D triangular-lattice due to minor Fe doping. Synchrotron x-ray diffraction studies reveal step-like structural transitions close to antiferroelectric and antiferromagnetic transitions. Appearance of a new structural transition at antiferromagnetic ordering indicates the presence of magnetoelastic coupling.

Three-Dimensional Magnetic Correlations in Multiferroic LuFe2O4

Physical Review Letters, 2008

We present single crystal neutron diffraction measurements on multiferroic LuFe2O4. Magnetic reflections are observed below transitions at 240 and 175 K indicating that the magnetic interactions in LuFe2O4 are 3-dimensional (3D) in character. The magnetic structure is refined as a ferrimagnetic spin configuration below the 240 K transition. Below 175 K a significant broadening of the magnetic peaks is observed along with the build up of a diffuse component to the magnetic scattering. 75.30.Kz, 28.20.Cz, 25.40.Dn Materials that offer the possibility of simultaneously controlling magnetic and electric degrees of freedom are the subject of intense interest . Recently, multiferroic materials have been identified that show large coupling between electric and magnetic degrees of freedom. Ferroelectricity driven by either magnetic or charge ordering appears to be the origin of the large coupling and, hence, understanding the underlying electronic interactions is crucial for further insight into multiferroicity [1].

Giant Room–Temperature Magnetodielectric Response in the Electronic Ferroelectric LuFe2O4

Advanced Materials, 2006

Large changes in the dielectric constant of LuFe 2 O 4 are observed at room temperature upon application of small magnetic fields. Such behavior is unprecedented and indicates a strong coupling of spins and electric dipoles at room temperature. This could give rise to a new generation of devices based on multiferroic behavior. The ferroelectricity of LuFe 2 O 4 appears to result from ordering of Fe 2+ and Fe 3+ , and a new structural model for this unique mechanism is proposed. Recent proposals to develop novel multifunctional storage components for microelectronics have led to an intense interest in materials in which ferroelectric and magnetic order parameters are coupled. [1,2] Devices fabricated from such multiferroic materials could store information through both the electric and magnetic polarization of the bit, providing an additional degree of freedom in designing memory elements. Furthermore, magnetodielectric coupling in multiferroics may be particularly useful in designing devices to read magnetic storage systems. Current read heads rely on magnetoresitive materials, which generate heat and are sensitive to thermal noise. Capacitive readings under magnetic fields can be accomplished with no or very small amounts of heat produced, and capacitance measurements can be more sensitive than resistive measurements, which could allow the magnetic bit density to be increased. After the first experimental realization of magnetoelectric coupling in antiferromagnetic Cr 2 O 3 , [3] similar effects have been observed at low temperatures in several other antiferromagnetic materials, including BaMnF 4 , [4] GdVO 4 , [5] GdAlO 3 , [6] DyPO 4 , [7] Gd 2 CuO 4 , [8] YMnO 3 , [9] and EuTiO 3. [10] Among the ferromagnetic insulators investigated, large magnetodielectric coupling near ferromagnetic Curie temperatures was found in BiMnO 3 at 100 K [11] and in Se-CuO 3 at 25 K. [12] Very recently, we reported a large magnetodielectric effect in La 2 NiMnO 6 close to its ferromagnetic Curie temperature of 285 K. [13] None of these materials showed a significant change in dielectric constant with changing mag-COMMUNICATIONS

Manipulating magnetoelectric energy landscape in multiferroics

Nature Communications, 2020

Magnetoelectric coupling at room temperature in multiferroic materials, such as BiFeO3, is one of the leading candidates to develop low-power spintronics and emerging memory technologies. Although extensive research activity has been devoted recently to exploring the physical properties, especially focusing on ferroelectricity and antiferromagnetism in chemically modified BiFeO3, a concrete understanding of the magnetoelectric coupling is yet to be fulfilled. We have discovered that La substitutions at the Bi-site lead to a progressive increase in the degeneracy of the potential energy landscape of the BiFeO3 system exemplified by a rotation of the polar axis away from the 〈111〉pc towards the 〈112〉pc discretion. This is accompanied by corresponding rotation of the antiferromagnetic axis as well, thus maintaining the right-handed vectorial relationship between ferroelectric polarization, antiferromagnetic vector and the Dzyaloshinskii-Moriya vector. As a consequence, La-BiFeO3 films ...

Magnetic ground state of the multiferroic hexagonal LuFeO3

Physical Review B, 2018

The structural, electric, and magnetic properties of bulk hexagonal LuFeO 3 are investigated. Single phase hexagonal LuFeO 3 has been successfully stabilized in the bulk form without any doping by sol-gel method. The hexagonal crystal structure with P 6 3 cm space group has been confirmed by x-ray-diffraction, neutron-diffraction, and Raman spectroscopy study at room temperature. Neutron diffraction confirms the hexagonal phase of LuFeO 3 persists down to 6 K. Further, the x-ray photoelectron spectroscopy established the 3+ oxidation state of Fe ions. The temperature-dependent magnetic dc susceptibility, specific heat, and neutron-diffraction studies confirm an antiferromagnetic ordering below the Néel temperature (T N) ∼ 130 K. Analysis of magnetic neutron-diffraction patterns reveals an in-plane (ab-plane) 120 • antiferromagnetic structure, characterized by a propagation vector k = (0 0 0) with an ordered moment of 2.84 μ B /Fe 3+ at 6 K. The 120 • antifferomagnetic ordering is further confirmed by spin-orbit coupling density functional theory calculations. The on-site coulomb interaction (U) and Hund's parameter (J H) on Fe atoms reproduced the neutron-diffraction 1 spin pattern among the Fe atoms. P-E loop measurements at room temperature confirm an intrinsic ferroelectricity of the sample with remnant polarization P r ∼ 0.18 μC/cm 2. A clear anomaly in the dielectric data is observed at ∼T N revealing the presence of magnetoelectric coupling. A change in the lattice constants at T N has also been found, indicating the presence of a strong magnetoelastic coupling. Thus a coupling between lattice, electric, and magnetic degrees of freedom is established in bulk hexagonal LuFeO 3 .

Synthetic magnetoelectric coupling in a nanocomposite multiferroic

arXiv (Cornell University), 2014

Given the paucity of single phase multiferroic materials (with large ferromagnetic moment), composite systems seem an attractive solution in the quest to realize magnetoelectric coupling between ferromagnetic and ferroelectric order parameters. Despite having antiferromagnetic order, BiFeO 3 (BFO) has nevertheless been a key material in this quest due to excellent ferroelectric properties at room temperature. We studied a superlattice composed of 8 repetitions of 6 unit cells of La 0.7 Sr 0.3 MnO 3 (LSMO) grown on 5 unit cells of BFO. Significant net uncompensated magnetization in BFO is demonstrated using polarized neutron reflectometry in an insulating superlattice. Remarkably, the magnetization enables magnetic field to change the dielectric properties of the superlattice, which we cite as an example of synthetic magnetoelectric coupling. Importantly, this controlled creation of magnetic moment in BFO suggests a much needed path forward for the design and implementation of integrated oxide devices for next generation magnetoelectric data storage platforms. The ability to control magnetization, M, via electric fields or alternatively electric polarization, P, via magnetic fields enables a myriad of technological innovations in information storage, sensing, and computing. For example, Oersted-fields that are presently used to switch the magnetic state of commercial magnetic tunnel junctions, are spatially extended and require modest current to produce. These attributes limit the areal density of magnetic tunnel junctions. Because electrostatic fields can be confined and require very little current to produce, integration of a multiferroic composite-a system of different constituents with coupled M and P order parameters-into a magnetic tunnel junction might enable the "single memory solution"-non-volatile memory that is more energy efficient, faster, higher capacity and more affordable than competing technologies. BiFeO 3 (BFO) is a single phase multiferroic material which exhibits magnetoelectric coupling between antiferromagnetic 1 and ferroelectric 2 order parameters to temperatures hundreds of degrees above room temperature. As such, BFO is potentially an attractive technological material. However, important challenges impede progress. First, the electric polarization vector can be along any of eight equivalent [111] directions, thus, the polarization domain state can be ill-defined/complex. 3 Second, the sub-lattice magnetization has six equivalent easy axes in the plane normal to the electric polarization vector, thus, the antiferromagnetic