We welcome Takayuki, Weronika, and Teodor in MULFOX to work on spintronics materials and devices

Written by Palma Scarcia on . Posted in FEATURED, News.

Dr. Takayuki Shiino and Dr. Weronika Janus joined MULFOX as postdoctoral researchers, and Teodor Apetrei joined as a Ph.D. candidate. We warmly welcome them to the group and wish them success.

Takayuki received his BSc in Physics (2013) and MSc in Materials Science and Engineering (2016) from Tokyo Institute of Technology (Japan) and KAIST (South Korea), respectively. He received his Ph.D. from Nagoya University (Japan) in 2019 with a thesis on a quantum critical phenomenon in heavy-fermion materials. After the PhD, he experienced two postdoctoral researches: Uppsala University (2019 – 2021, Sweden) and KAIST (2022 – 2024, South Korea) for the studies of quasicrystals and spintronics, respectively. His postdoctoral research at MULFOX focuses on spintronic devices with insulating ferrimagnetic materials.

Weronika studied at AGH University of Krakow, Poland, where she obtained her BSc in Biomedical Engineering (2018), MSc in Biomedical Engineering – Bionanotechnology (2019), and PhD in Physics (2014). During her PhD, she focused on the strain manipulation of magnetic properties in antiferromagnetic thin films. Her current research interest is in developing innovative magnetic insulator-based spintronic memory devices, where the information can be written and read by all-electrical means

Teodor obtained his BSc. degree in Computational Physics at University Alexandru Ioan Cuza Iasi (Romania, 2020) and his MSc. degree in Applied and Engineering Physics at Technische Universitat Munchen (Germany, 2023). The main focus of his current research is the growth and engineering of magnetic oxide and nitride thin films by magnetron sputtering with tunable interfacial chiral magnetism and perpendicular anisotropy.

We organize an international School on Topological Interfaces, 30-31 May 2024, ICMAB-CSIC Barcelona

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This is the 3rd Edition of “ICMAB Schools on Frontiers in Materials Science and Condensed Matter”. Previous editions were “Angle Resolved Photoemission Spectroscopy (https://arpes2023.icmab.es/)” and “Orbital currents in solids (https://orbitalcurrents2023.icmab.es/)”

More information at https://topologicalinterfaces2024.icmab.es/

Gervasi Herranz and Gyanendra Singh participate in the APS March Meeting 2024

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Gervasi Herranz delivers a talk (IN-PERSON MEETING) on 6th March at 2:18 PM at the APS March Meeting 2024 (Minneapolis, Minnesota, USA) in Session N04: Ordering Phenomena in Spin-Orbit Coupled Systems

Room: L100D The talk is N04.00011 : Electromagnetic detection of spin-orbit entangled states in Jahn-Teller Mn3+ ions”.
Gyanendra Singh delivers a talk (VIRTUAL MEETING) on 6th March at 12:30 PM the APS March Meeting 2024 (Minneapolis, Minnesota, USA) Abstract: HH05.00006 : Stoichiometric control of 2D superconductivity and mobility at SrTiO3-based interfaces.

Absence of 3a0 charge density wave order in the infinite-layer nickelate NdNiO2

Written by Palma Scarcia on . Posted in FEATURED, News.

C. T. Parzyck, N. K. Gupta, Y. Wu, V. Anil, L. Bhatt, M. Bouliane, R. Gong, B. Z. Gregory, A. Luo, R. Sutarto, F. He, Y.-D. Chuang, T. Zhou, G. Herranz, L. F. Kourkoutis, A. Singer, D. G. Schlom, D. G. Hawthorn & K. M. Shen

Nat. Mater. (2024)

DOI: https://doi.org/10.1038/s41563-024-01797-0

Abstract

A hallmark of many unconventional superconductors is the presence of many-body interactions that give rise to broken-symmetry states intertwined with superconductivity. Recent resonant soft X-ray scattering experiments report commensurate 3a0 charge density wave order in infinite-layer nickelates, which has important implications regarding the universal interplay between charge order and superconductivity in both cuprates and nickelates. Here we present X-ray scattering and spectroscopy measurements on a series of NdNiO2+x samples, which reveal that the signatures of charge density wave order are absent in fully reduced, single-phase NdNiO2. The 3a0 superlattice peak instead originates from a partially reduced impurity phase where excess apical oxygens form ordered rows with three-unit-cell periodicity. The absence of any observable charge density wave order in NdNiO2 highlights a crucial difference between the phase diagrams of cuprate and nickelate superconductors.

Enhanced spin current transmissivity in Pt/CoFe2O4 bilayers with thermally induced interfacial magnetic modification

Written by Palma Scarcia on . Posted in FEATURED, News.

M. Gamino, A. B. Oliveira, D. S. Maior, P. R. T. Ribeiro, F. L. A. Machado, T. J. A. Mori, M. A. Correa, F. Bohn, R. L. Rodríguez-Suárez, J. Fontcuberta, and S. M. Rezende

Phys. Rev. B 2023, 108, 224402;

DOI: https://doi.org/10.1103/PhysRevB.108.224402

Abstract

We report on processes of generation of spin current and conversion into charge current in CoFe2O4/Pt bilayers by means of spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) experiments. Specifically, we explore (001) full-textured CoFe2O4 (CFO) thin films grown onto (001)-oriented SrTiO3 substrates, covered with Pt layers deposited under two different conditions: one at room temperature and another at high temperature (400∘C). The x-ray absorption spectroscopy measurements indicate that the Pt layer deposited at high temperature induces an interfacial magneticlike phase (Fe,Co)-Pt alloy, which influences the magnetic behavior of the structure and is responsible for the enhancement of the spin transmission at the interface. By analyzing the SMR data, we conclude that collinear and noncollinear magnetic domains coexist at the CFO-(Fe,Co)-Pt interface. By combining the data from the SMR and SSE measurements, we obtain the ratios between the values of the spin Hall angle (θSH) and between the ones of the spin-mixing conductance (g↑↓eff) in the two samples. We demonstrate that while the value of θSH decreases by one-half with the heat treatment, the value of g↑↓eff increases by more than one order of magnitude. We interpret the increase of g↑↓eff in terms of unexpected magnetic reconstructions, which produce an enhancement of the magnetic moment arisen at the interface. Since the spin-mixing conductance determines the efficiency of the spin current transmission through the interface, the spinel ferrite cobalt in contact with a normal metal with a suitable heat treatment becomes a promising material for spintronics device applications.

Orbital Currents School 2023

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The ICMAB organized Orbital Currents School 2023 conclued. 

With a participation of about 70 attendants in-person and 110 on line, the School has finished. A very exciting Introductory lecture by Tatiana G. Rappoport, was followed by lectures by Aurélien Manchon, Dongwook Go, Enric Canadell, Hyun-Woo Lee and Can Onur Avci, which motivated living discussions, comments and suggested intriguing prospectives.

Electrical characterization and extraction of activation energies of the defect states in the LaAlO3/SrTiO3 heterostructure

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Yoann Lechaux, Yu Chen; Albert Minj, Florencio Sánchez, Gervasi Herranz, Laurence Méchin, Bruno Guillet

Appl. Phys. Lett. 121, 081904 (2022); DOI: https://doi.org/10.1063/5.0101255

 

Abstract

In this work, we study the electronic properties of defects in the LaAlO3/SrTiO3 heterostructure, which is known to host a high mobility two-dimensional electron gas (2DEG) at the interface. This 2DEG also shows photoconductance, which could be related to defects that act as deep center trapping and releasing carriers by interaction with light. This phenomenon has raised an interest for the identification of deep energy levels in the LaAlO3/SrTiO3 heterostructure. We have studied the defect state properties using electrical characterization such as capacitance–voltage (C–V), current–voltage (I–V) measurements, and deep-level transient Fourier spectroscopy (DLTFS). From C–V and I–V analyses, a hysteresis was observed indicating an effect of mobile charges in the LaAlO3. Using DLTFS, we identify three defect states located at around 0.17 eV below conduction band and at 0.23 and 0.26 eV above the valence band. These defect states were attributed to defects in SrTiO3 such as strontium vacancies or titanium vacancies. We identify a fourth defect state having an energy of about 0.69 eV below the conduction band that could be related to oxygen vacancies in LaAlO3 or in SrTiO3. In addition, the observation of an effect of the electric field with DLTFS indicated that oxygen vacancies might be involved in Fowler–Nordheim or trap-assisted tunneling through the LaAlO3 layer.

MnTa2N4: A Ternary Nitride Spinel with a Strong Magnetic Frustration

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Rafael Trócoli, Carlos Frontera, Judith Oró-Solé, Clemens Ritter, Pere Alemany, Enric Canadell, M. Rosa Palacín, Josep Fontcuberta, and Amparo Fuertes

Chem. Mater. 2022, 34, 13, 6098–6107 (2022);  DOI:doi.org/10.1021/acs.chemmater.2c01240

Abstract

Magnetic frustration results from competing magnetic interactions and leads to unusual ground states, ranging from non-collinear magnetic orders to spin liquids (SLs), opening the path to new physics and emerging properties. We report the engineered magnetic interaction design and synthesis of the new ternary nitride MnTa2N4 with a normal spinel structure, where the magnetic cations Mn2+ occupy exclusively the tetrahedral sites forming a diamond lattice.
Although the magnetic interactions are strongly antiferromagnetic (θCW ≈ −140 K), a long-range magnetic order is not established, but a smooth magnetic anomaly is observed at T* ≈ 5.1 K, fingerprinting a large magnetic frustration. A short-range helicoidal magnetic order emerges at low temperatures. The ordered moment is ≈70% of the expected magnetic moment of Mn2+ ions and a large part (≈28%) of the spin entropy remains at 400 mK, signaling the coexistence of a helicoidal order with spin-glass-like or SL textures. First-principles calculations unveil an unexpected large direct Mn–Mn exchange interaction that balances the superexchange and accounts for the magnetic frustration. These findings open new avenues toward the design of quantum materials.
 

Voltage-driven strain-mediated modulation of exchange bias in Ir20Mn80/Fe80Ga20/Ta/⟨011⟩-oriented PMN-32PT heterostructures

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E. Demirci, J. de Rojas, A. Quintana, I. Fina, E. Menéndez, and J. Sort

Appl. Phys. Lett. 121, 081904 (2022);  DOI:doi.org/10.1063/5.0091231

Abstract

Manipulation of exchange bias with electric field is appealing to boost energy efficiency in spintronic devices. Here, this effect is shown at room temperature in Ir20Mn80/Fe80Ga20/Ta layers grown onto ⟨011⟩-oriented PMN-32PT single crystals. After magnetic field-cooling (FC) along the [01-1] and [100] in-plane directions of PMN-32PT and upon allowing the system to relax through consecutive hysteresis loops (training effect), the exchange bias field (HEB) is measured under the action of voltage (out-of-plane poling). Depending on the applied voltage (magnitude and sign), HEB can either increase or decrease with respect to its value at 0 V. The relative variations of HEB are 24% and 5.5% after FC along the [01-1] and [100] directions, respectively.

These results stem from strain-mediated magnetoelectric coupling. The applied electric field causes changes in the coercivity and the squareness ratio of the films, suggesting a reorientation of the effective magnetic easy axis in Fe80Ga20. However, larger HEB values are observed when the squareness ratio is lower. It is claimed that the effect of voltage is equivalent to an in-plane component of an applied magnetic field oriented perpendicular to the cooling field direction. Perpendicular in-plane magnetic fields have been shown to induce an increase in exchange bias in some ferromagnetic/antiferromagnetic systems due to partial recovery of the untrained antiferromagnetic state. Remarkably, here, this effect is directly induced with voltage, therefore enhancing energy efficiency.

 

Two-gap s±-wave superconductivity at an oxide interface

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G. Singh, G. Venditti, G. Saiz, G. Herranz, F. Sánchez, A. Jouan, C. Feuillet-Palma, J. Lesueur, M. Grilli, S. Caprara, and N. Bergeal

Phys. Rev. B 105, 064512 (2022);  DOI:doi.org/10.1103/PhysRevB.105.064512

Abstract

After half a century of debate, superconductivity in doped SrTiO3 has come to the fore again with the discovery of interfacial superconductivity in the LaAlO3/SrTiO3 heterostructures. While these interfaces share the interesting properties of bulk SrTiO3 , quantum confinement generates a complex band structure involving bands with different orbital symmetries whose occupancy is tunable by electrostating doping.
Multigap superconductivity has been predicted to emerge in LaAlO3/SrTiO3 at large doping, with a Bose-Einstein condensation character at the Lifshtiz transition. In this article, we report on the measurement of the upper critical magnetic field Hc2 of superconducting (110)-oriented LaAlO3/SrTiO3 heterostructures and evidence a two-gap superconducting regime at high doping. Our results are quantitatively explained by a theoretical model based on the formation of an unconventional s±-wave superconducting state with a repulsive coupling between the two condensates.

Enhanced electroresistance endurance of capped Hf0.5Zr0.5O2 ultrathin epitaxial tunnel barriers

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Xiao Long, Huan Tan, Saúl Estandía, Jaume Gazquez, Florencio Sánchez, Ignasi Fina and Josep Fontcuberta

APL Materials 10, 031114 (2022);  DOI:doi.org/10.1063/5.0076865

Abstract

Electroresistance in ultrathin Hf0.5Zr0.5O2 (HZO) films is pivotal toward the implementation of hafnia-based ferroelectrics in electronics. Here, we show that the electroresistance yield and endurance of large capacitors (∼314 µm2) of epitaxial HZO films only 2.2 nm thick grown on SrTiO3 or GdScO3 can be improved using 1 nm SrTiO3 capping layers. It is argued that the main role of the capping layer is to minimize charge transport along grain boundaries, and, thus, a similar strategy can be explored in polycrystalline films
Electroresistance in ultrathin Hf0.5Zr0.5O2 (HZO) films is pivotal toward the implementation of hafnia-based ferroelectrics in electronics. Here, we show that the electroresistance yield and endurance of large capacitors (∼314 µm2) of epitaxial HZO films only 2.2 nm thick grown on SrTiO3 or GdScO3 can be improved using 1 nm SrTiO3 capping layers. It is argued that the main role of the capping layer is to minimize charge transport along grain boundaries, and, thus, a similar strategy can be explored in polycrystalline films
 

Impact of non-ferroelectric phases on switching dynamics in epitaxial ferroelectric Hf0.5Zr0.5O2 films

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Tingfeng Song, Florencio Sánchez, and Ignasi Fina

APL Materials 10, 031108 (2022);  DOI:doi.org/10.1063/5.0083661

Abstract

Determining the switching speed and mechanisms in ferroelectric HfO2 is essential for applications. Switching dynamics in orthorhombic epitaxial ferroelectric Hf0.5Zr0.5O2 films with either significant or negligible presence of monoclinic paraelectric phase is characterized.
Switching spectroscopy reveals that the polarization dynamics in pure orthorhombic ferroelectric phase films can be modeled by the Kolmogorov–Avrami–Ishibashi mechanism with large characteristic time (≈1 µs), which is shortened in fatigued junctions. The long switching time indicates that non-archetypical switching mechanisms occur and that ionic motion or other extrinsic contributions might be at play. Films containing a higher amount of paraelectric monoclinic phase show a shorter switching time of 69 ns, even in pristine state, for applied electric field parallel to the imprint field, enabling synaptic-like activity using fast electric stimuli. Thus, the presence of defects or paraelectric phase is found to improve the switching speed, contrary to what one can expect a priori.
 

Improved polarization and endurance in ferroelectric Hf0.5Zr0.5O2 films on SrTiO3(110)

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Tingfeng Song, Huan Tan, Saúl Estandía, Jaume Gàzquez, Martí Gich, Nico Dix, Ignasi Fina and Florencio Sánchez

Nanoscale, 2022,14, 2337-2343 (2022);  DOI:10.1039/D1NR06983G

Abstract

The metastable orthorhombic phase of Hf0.5Zr0.5O2 (HZO) can be stabilized in thin films on La0.67Sr0.33MnO3 (LSMO) buffered (001)-oriented SrTiO3 (STO) by intriguing epitaxy that results in (111)-HZO oriented growth and robust ferroelectric properties. Here, we show that the orthorhombic phase can also be epitaxially stabilized on LSMO/STO(110), presenting the same out-of-plane (111) orientation but a different distribution of the in-plane crystalline domains.
The remanent polarization of HZO films with a thickness of less than 7 nm on LSMO/STO(110) is 33 μC cm−3, which corresponds to a 50% improvement over equivalent films on LSMO/STO(001). Furthermore, HZO on LSMO/STO(110) presents higher endurance, switchable polarization is still observed up to 4 × 1010 cycles, and retention of more than 10 years. These results demonstrate that tuning the epitaxial growth of ferroelectric HfO2, here using STO(110) substrates, allows the improvement of functional properties of relevance for memory applications.
 

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