arXiv subjects

I. Fina

Publications and source records attributed to I. Fina.

14 recordsLinked to original sources

arXiv2021

Giant Tuning of Electronic and Thermoelectric Properties by Epitaxial Strain in p-Type Sr-Doped LaCrO3 Transparent Thin Films

The impact of epitaxial strain on the structural, electronic, and thermoelectric properties of p-type transparent Sr-doped LaCrO3 thin films has been investigated. For this purpose, high-quality fully strained La0.75Sr0.25CrO3 (LSCO) epitaxial thin films were grown by molecular beam epitaxy on three different (pseudo)cubic (001)-oriented perovskite oxide substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and DyScO3. The lattice mismatch between the LSCO films and the substrates induces in-plane strain ranging from -2.06% (compressive) to +1.75% (tensile). The electric conductivity can be controlled over 2 orders of magnitude, ranging from 0.5 S/cm (tensile strain) to 35 S/cm (compressive strain). Consistently, the Seebeck coefficient S can be finely tuned by a factor of almost 2 from 127 microV/K (compressive strain) to 208 microV/K (tensile strain). Interestingly, we show that the thermoelectric power factor can consequently be tuned by almost 2 orders of magnitude. The compressive strain yields a remarkable enhancement by a factor of 3 for 2% compressive strain with respect to almost relaxed films. These results demonstrate that epitaxial strain is a powerful lever to control the electric properties of LSCO and enhance its thermoelectric properties, which is of high interest for various devices and key applications such as thermal energy harvesters, coolers, transparent conductors, photocatalyzers, and spintronic memories.

cond-mat.mtrl-sci↗

arXiv2019

Enhanced ferroelectricity in epitaxial Hf0.5Zr0.5O2 thin films integrated with Si(001) using SrTiO3 templates

SrTiO3 templates have been used to integrate epitaxial bilayers of ferroelectric Hf0.5Zr0.5O2 and La2/3Sr1/3MnO3 bottom electrode on Si(001). The Hf0.5Zr0.5O2 films show enhanced properties in comparison to equivalent films on SrTiO3(001) single crystalline substrates. The films, thinner than 10 nm, have very high remnant polarization of 34 uC/cm2. Hf0.5Zr0.5O2 capacitors at operating voltage of 4 V present long retention time well beyond 10 years and high endurance against fatigue up to 109 cycles. The robust ferroelectric properties displayed by the epitaxial Hf0.5Zr0.5O2 films on Si(001) using SrTiO3 templates paves the way for the monolithic integration on silicon of emerging memory devices based on epitaxial HfO2.

physics.app-ph↗

arXiv2017

Spintronic Functionalities in Multiferroic Oxide-based Heterostructures

The list of materials systems displaying both electric and magnetic long range order is short. Oxides, however, concentrate numerous examples of multiferroicity with, in some cases, a large magnetoelectric coupling. As a result, a fruitful research field has emerged contemporaneously with the consolidation of spintronic. The synergy between multiferroics and spintronics was meant to be inevitable and hence the characterization of spintronic functionalities in multiferroic materials is rather abundant. The aim of the present chapter is to review the oxide heterostructures where magnetoelectric coupling is demonstrated by means of spintronic functionalities (i.e. magnetoresistance, anisotropic magnetoresistance, giant magnetoresistance or tunnel magnetoresistance).

cond-mat.mtrl-sci↗

arXiv2017

Photoferroelectric oxides

Giant photovoltaic effect due to bulk photovoltaic effect observed in multiferroic BiFeO3 thin films has triggered a renewed interest on photoferroelectric materials for photovoltaic applications. Tremendous advance has been done to improve power conversion efficiency (up to up to 8.1%) in photoferroelectrics via absorption increase using narrow bandgap ferroelectrics. Other strategies, as it is the more efficient use of ferroelectric internal electric field, are ongoing. Moreover, as a by-product, several progress have been also achieved on photostriction that is the photo-induced deformation phenomenon. Here, we review ongoing and promising routes to improve ferroelectrics photoresponse.

cond-mat.mtrl-sci↗

arXiv2016

Electric control of antiferromagnets

In the past five years, most of the paradigmatic concepts employed in spintronics have been replicated substituting ferromagnets by antiferromagnets in critical parts of the devices. The numerous research efforts directed to manipulate and probe the magnetic moments in antiferromagnets have been gradually established a new and independent field known as antiferromagnetic spintronics. In this paper, we focus on the electrical control and detection of antiferromagnetic moments at a constant temperature. We address separately the experimental results concerning insulating and metallic thin films as they correspond to voltage and electrical current controlled devices, respectively. First, we present results on the voltage control of antiferromagnetic order in insulating thin films. The experiments show that voltage pulses can switch the chirality of a modulated antiferromagnetic structure. Second, we describe the recent advances in metallic antiferromagnetic systems. We present results obtained with the first USB-operated portable device able to perform the non-volatile electrical current-induced switching of an antiferromagnet combined with magnetoresistive readout at room temperature. We discuss on potential applications that can be realized using antiferromagnetic memory cells.

cond-mat.mtrl-sci↗

arXiv2016

An invisible non-volatile solid-state memory

Information technologies require entangling data stability with encryption for a next generation of secure data storage. Current magnetic memories, ranging from low-density stripes up to high-density hard drives, can ultimately be detected using routinely available probes or manipulated by external magnetic perturbations. Antiferromagnetic resistors feature unrivalled robustness but the stable resistive states reported scarcely differ by more than a fraction of a percent at room temperature. Here we show that the metamagnetic (ferromagnetic to antiferromagnetic) transition in intermetallic Fe0.50Rh0.50 can be electrically controlled in a magnetoelectric heterostructure to reveal or cloak a given ferromagnetic state. From an aligned ferromagnetic phase, magnetic states are frozen into the antiferromagnetic phase by the application of an electric field, thus eliminating the stray field and likewise making it insensitive to external magnetic field. Application of a reverse electric field reverts the antiferromagnetic state to the original ferromagnetic state. Our work demonstrates the building blocks of a feasible, extremely stable, non-volatile, electrically addressable, low-energy dissipation, magnetoelectric multiferroic memory.

cond-mat.mtrl-sci↗

arXiv2016

Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15 % has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature.

cond-mat.mtrl-sci↗

arXiv2015

Optical investigation of magneto-structural phase transition in FeRh

Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near infrared spectral ranges. This phenomenon was used to measure the phase transition temperature in FeRh films with thicknesses from 6 to 100 nm and it was observed that the hysteretic transition region broadens significantly in the thinner films.

cond-mat.mtrl-sci↗

arXiv2015

Prospect for antiferromagnetic spintronics

Exploiting both spin and charge of the electron in electronic micordevices has lead to a tremendous progress in both basic condensed-matter research and microelectronic applications, resulting in the modern field of spintronics. Current spintronics relies primarily on ferromagnets while antiferromagnets have traditionally played only a supporting role. Recently, antiferromagnets have been revisited as potential candidates for the key active elements in spintronic devices. In this paper we review approaches that have been employed for reading, writing, and storing information in antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2015

Room-temperature antiferromagnetic memory resistor

The bistability of ordered spin states in ferromagnets (FMs) provides the magnetic memory functionality. Traditionally, the macroscopic moment of ordered spins in FMs is utilized to write information on magnetic media by a weak external magnetic field, and the FM stray field is used for reading. However, the latest generation of magnetic random access memories demonstrates a new efficient approach in which magnetic fields are replaced by electrical means for reading and writing. This concept may eventually leave the sensitivity of FMs to magnetic fields as a mere weakness for retention and the FM stray fields as a mere obstacle for high-density memory integration. In this paper we report a room-temperature bistable antiferromagnetic (AFM) memory which produces negligible stray fields and is inert in strong magnetic fields. We use a resistor made of an FeRh AFM whose transition to a FM order 100 degrees above room-temperature, allows us to magnetically set different collective directions of Fe moments. Upon cooling to room-temperature, the AFM order sets in with the direction the AFM moments pre-determined by the field and moment direction in the high temperature FM state. For electrical reading, we use an antiferromagnetic analogue of the anisotropic magnetoresistance (AMR). We report microscopic theory modeling which confirms that this archetypical spintronic effect discovered more than 150 years ago in FMs, can be equally present in AFMs. Our work demonstrates the feasibility to realize room-temperature spintronic memories with AFMs which greatly expands the magnetic materials base for these devices and offers properties which are unparalleled in FMs.

cond-mat.mtrl-sci↗

arXiv2013

Anisotropic magnetoresistance in antiferromagnetic semiconductor Sr2IrO4 epitaxial heterostructure

Lord Kelvin with his discovery of the anisotropic magnetoresistance (AMR) phenomenon in Ni and Fe was 70 years ahead of the formulation of relativistic quantum mechanics the effect stems from, and almost one and a half century ahead of spintronics whose first commercial applications relied on the AMR. Despite the long history and importance in magnetic sensing and memory technologies, the microscopic understanding of the AMR has struggled to go far beyond the basic notion of a relativistic magnetotransport phenomenon arising from combined effects on diffusing carriers of spin-orbit coupling and broken symmetry of a metallic ferromagnet. Our work demonstrates that even this seemingly generic notion of the AMR phenomenon needs revisiting as we observe the ohmic AMR effect in a nano-scale film of an antiferromagnetic (AFM) semiconductor Sr2IrO4 (SIO). Our work opens the recently proposed path for integrating semiconducting and spintronic technologies in AFMs. SIO is a particularly favorable material for exploring this path since its semiconducting nature is entangled with the AFM order and strong spin-orbit coupling. For the observation of the low-field Ohmic AMR in SIO we prepared an epitaxial heterostructure comprising a nano-scale SIO film on top of an epilayer of a FM metal La2/3Sr1/3MnO3 (LSMO). This allows the magnetic field control of the orientation of AFM spins in SIO via the exchange spring effect at the FM-AFM interface.

cond-mat.mtrl-sci↗

arXiv2013

Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling

Tunneling junctions containing no ferromagnetic elements have been fabricated and we show that distinct resistance states can be set by field cooling the devices from above the Néel along different orientations. Variations of the resistance up to 10% are found upon field cooling in applied fields of 2T, in-plane or out of plane. Below TN, we found that the metastable states are insensitive to magnetic fields thus constituting a memory element robust against external magnetic fields. Our work provides the demonstration of an electrically readable magnetic memory device, which contains no ferromagnetic elements and stores the information in an antiferromagnetic active layer.

cond-mat.mes-hall↗

arXiv2010

Ferroelectricity and strain effects in orthorhombic YMnO3 thin films

We report on the dielectric properties of epitaxial [001] and [100]-textured thin films of antiferromagnetic orthorhombic YMnO3 and their variation under compressive epitaxial strain. It is found that weakly strained YMnO3 films are ferroelectric with a polarization along c-axis switchable by 90 degrees by an external magnetic field. When reducing film thickness and increasing epitaxial strain, the ferroelectric order is progressively suppressed. Analysis of structural, dielectric and magnetic data indicates that suppression of ferroelectricity when reducing thickness is accompanied by an enlarged ratio a/b of the in-plane cell parameters of the orthorhombic structure and the appearance of a net magnetization. All results can be well described by considering the multiferroic phase diagram of orthorhombic manganites.

cond-mat.mtrl-sci↗

arXiv2010

Magnetization Reversal by Electric-Field Decoupling of Magnetic and Ferroelectric Domains Walls in Multiferroic-Based Heterostructures

We demonstrate that the magnetization of a ferromagnet in contact with an antiferromagnetic multiferroic (LuMnO3) can be speedily reversed by electric field pulsing, and the sign of the magnetic exchange bias can switch and recover isothermally. As LuMnO3 is not ferroelastic, our data conclusively show that this switching is not mediated by strain effects but is a unique electric-field driven decoupling of the ferroelectric and ferromagnetic domains walls. Their distinct dynamics are essential for the observed magnetic switching.

cond-mat.mtrl-sci↗