J.-C. Rojas-Sánchez

Centre National de la Recherche Scientifique

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S. Petit

Centre National de la Recherche Scientifique

L. Vila

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

H. Jaffrès

Laboratoire Albert Fert

Jean‐Marie George

Laboratoire Albert Fert

Jean‐Philippe Attané

CEA Grenoble

S. Mangin

Institut Jean Lamour

A. Fert

Centre National de la Recherche Scientifique

M. Hehn

Institut Jean Lamour

Alberto Anadón

IMDEA Nanoscience

Nicolas Reyren

Université Paris-Saclay

Cooperative Institutions

Centre National de la Recherche Scientifique

218

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

Université Paris-Saclay

Université Grenoble Alpes

CEA Grenoble

Laboratoire Albert Fert

Université Paris-Sud

Institut Jean Lamour

Université de Lorraine

Institut Nanosciences et Cryogénie

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Thermal Spin-Current Generation in the Multifunctional Ferrimagnet Ga0.6Fe1.4O3

Physical Review Applied (2022)

Alberto Anadón Élodie Martin Suvidyakumar Homkar Benjamin Meunier Maxime Vergès

In recent years, multifunctional materials have attracted increasing interest for magnetic memories and energy harvesting applications. Magnetic insulating materials are of special interest for this purpose, since they allow the design of more efficient devices due to the lower Joule heat losses. In this context, Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) is a good candidate for spintronics applications, since it can exhibit multiferroicity and presents a spin Hall magnetoresistance similar to the one observed in a yttrium iron garnet (YIG)/Pt bilayer. Here, we explore GFO utilizing thermo-spin measurements in an on-chip approach. By carefully considering the geometry of our thermo-spin devices we are able to quantify the spin Seebeck effect and the spin current generation in a GFO/Pt bilayer, obtaining a value comparable to that of YIG/Pt. This further confirms the promises of an efficient spin current generation with the possibility of an electric-field manipulation of the magnetic properties of the system in an insulating ferrimagnetic material.

Ferrimagnetism

Yttrium Iron Garnet

10.1103/physrevapplied.18.054087

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Citations (7)

Co$_2$ Mn-based Heusler compounds for spintronics: Chemical order and interplay between the magnetic damping and the underlying electronic structure

Charles Guillemard A. M. Bataille S. Petit J.-C. Rojas-Sánchez F. Bertran

Heusler compound

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Evidence for spin-to-charge conversion by Rashba coupling in metallic states at the Fe/Ge(111) interface

Nature Communications (2016)

Simón Oyarzún Arpita Nandy Fabien Rortais J.-C. Rojas-Sánchez Minh Tuan Dau

Abstract The spin–orbit coupling relating the electron spin and momentum allows for spin generation, detection and manipulation. It thus fulfils the three basic functions of the spin field-effect transistor. However, the spin Hall effect in bulk germanium is too weak to produce spin currents, whereas large Rashba effect at Ge(111) surfaces covered with heavy metals could generate spin-polarized currents. The Rashba spin splitting can actually be as large as hundreds of meV. Here we show a giant spin-to-charge conversion in metallic states at the Fe/Ge(111) interface due to the Rashba coupling. We generate very large charge currents by direct spin pumping into the interface states from 20 K to room temperature. The presence of these metallic states at the Fe/Ge(111) interface is demonstrated by first-principles electronic structure calculations. By this, we demonstrate how to take advantage of the spin–orbit coupling for the development of the spin field-effect transistor.

Rashba effect

Spin transistor

Spin–orbit interaction

Spin pumping

Spinplasmonics

Half-metal

10.1038/ncomms13857

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Citations (41)

Exchange-bias effect at La0.75Sr0.25MnO3/LaNiO

Physical Review B (2012)

J.-C. Rojas-Sánchez B. B. Nelson-Cheeseman M. Granada Elke Arenholz Laura Steren

We show that ferromagnetic/paramagnetic La${}_{0.75}$Sr${}_{0.25}$MnO${}_{3}$/LaNiO${}_{3}$ multilayers present an unexpected magnetic exchange-bias effect (EBE), observed in field-cooled magnetization loops. The exchange-bias field and the enhancement of the coercivity vanish around 50 K. We demonstrate that the oxidation state of the Ni and Mn cations changes from Mn${}^{3+}$-Ni${}^{3+}$ to Mn${}^{4+}$-Ni${}^{2+}$ in the layers close to the interface probed by x-ray absorption spectroscopy measurements. The variation of the valence states is accompanied by a change in the magnetic behavior of the cations at the La${}_{0.75}$Sr${}_{0.25}$MnO${}_{3}$/LaNiO${}_{3}$ interface, possibly giving rise to the formation of magnetic or magnetically frustrated regions that may pin the ferromagnetic La${}_{0.75}$Sr${}_{0.25}$MnO${}_{3}$ layers and explain the EBE.

Exchange bias

Lanio

10.1103/physrevb.85.094427

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Citations (75)

Current‐Induced Spin Torques on Single GdFeCo Magnetic Layers

Advanced Materials (2021)

David Céspedes-Berrocal Héloïse Damas S. Petit Davide Maccariello Ping Tang

Abstract Spintronics exploit spin‐orbit coupling (SOC) to generate spin currents, spin torques, and, in the absence of inversion symmetry, Rashba and Dzyaloshinskii–Moriya interactions. The widely used magnetic materials, based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this shortcoming, the common practice has been to utilize the large SOC of nonmagnetic layers of 5d heavy metals (HMs), such as Pt, to generate spin currents and, in turn, exert spin torques on the magnetic layers. Here, a new class of material architectures is introduced, excluding nonmagnetic 5d HMs, for high‐performance spintronics operations. Very strong current‐induced torques exerted on single ferrimagnetic GdFeCo layers, due to the combination of large SOC of the Gd 5d states and inversion symmetry breaking mainly engineered by interfaces, are demonstrated. These “self‐torques” are enhanced around the magnetization compensation temperature and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In other measurements, the very large emission of spin current from GdFeCo, 80% (20%) of spin anomalous Hall effect (spin Hall effect) symmetry is determined. This material platform opens new perspectives to exert “self‐torques” on single magnetic layers as well as to generate spin currents from a magnetic layer.

Ferrimagnetism

Point reflection

10.1002/adma.202007047

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Citations (63)

Nonmonotonic aftereffect measurements in perpendicular synthetic ferrimagnets

Physical review. B./Physical review. B (2018)

T. Fache H.S. Tarazona Jieyi Liu G. L. L’vova M. J. Applegate

Aftereffect measurements have been performed on synthetic ferrimagnets showing strong perpendicular magnetic anisotropy, namely (Co/Pt)/Ir/(Co/Pt), by measuring the magnetization of the sample as a function of time for several different applied magnetic fields. Unexpected magnetic relaxation has been observed. Indeed, for some particular applied magnetic fields, the magnetization as a function of time first plummets and then increases. This nonmonotonic aftereffect can be understood by considering the possible magnetic states and the transitions between those states. This understanding has been confirmed and detailed using magneto-optical Kerr effect (MOKE) microscopy. Indeed, the measurements show nucleation and propagation of a transient metastable magnetic configuration. Furthermore, we were able to obtain a good qualitative agreement between a simple one-dimensional model and the experimental observation. We could strongly support the hypothesis that this peculiar nonmonotonic behavior could be a very general feature that should be observed in any antiferromagnetically coupled system (synthetic ferrimagnets, synthetic antiferromagnets) with perpendicular magnetic anisotropy.

Metastability

10.1103/physrevb.98.064410

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Citations (15)

Isotropic spin and inverse spin Hall effect in epitaxial (111)-oriented Pt/Co bilayers

Physical Review Materials (2023)

Adrián Gudín Alberto Anadón Icíar Arnay R. Guerrero J. Julio Camarero

The spin-to-charge current interconversion in bilayers composed of ferromagnetic and nonmagnetic layers with strong spin-orbit coupling has garnered considerable attention due to its exceptional potential in advancing spintronics devices for data storage and logic applications. Platinum (Pt) stands out as one of the most effective materials for generating spin current. While the spin conversion efficiency is isotropic in polycrystalline Pt samples, an ongoing debate persists regarding its dependence on the crystalline direction in single crystalline samples. In this study, we aim to comprehensively evaluate the in-plane anisotropy of spin-charge interconversion using an array of complementary spin Hall and inverse spin Hall techniques with both incoherent and coherent excitation. Specifically, we investigate the spin-to-charge interconversion in epitaxial, (111)-oriented, Co/Pt bilayers with low surface roughness, as resulted from x-ray experiments. By varying the thickness of the Pt layer, we gain insights into the spin-charge interconversion in epitaxial Pt and highlight the effects of the interfaces. Our results demonstrate an isotropic behavior within the limits of our detection uncertainty. This finding significantly enhances our understanding of spin conversion in one of the most relevant systems in spintronics, and it paves the way for future research in this field.

Spin pumping

Spinplasmonics

10.1103/physrevmaterials.7.124412

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Citations (1)

Spin pumping and inverse spin Hall effect in germanium

Physical Review B (2013)

J.-C. Rojas-Sánchez M. Cubukcu A. Jain C. Vergnaud C. Portemont

We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room temperature. The spin current in germanium was generated by spin pumping from a CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch issue. A clear electromotive force was measured in Ge at the ferromagnetic resonance of CoFeB. The same study was then carried out on several test samples, in particular we have investigated the influence of the MgO tunnel barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to anisotropic magnetoresistance and anomalous Hall effect which is dominated by an asymmetric contribution with respect to the resonance field. We also found that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample annealing systematically lead to an increase of the signal. We propose a theoretical model based on the presence of localized states at the interface between the MgO tunnel barrier and Ge to account for these observations. Finally, all of our results are fully consistent with the observation of ISHE in heavily doped $n$-Ge and we could estimate the spin Hall angle at room temperature to be $\approx$0.001.

Spin pumping

Electromotive force

Spin Current

10.1103/physrevb.88.064403

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Citations (83)

Independence of spin-orbit torques from the exchange bias direction in Ni 81 Fe 19 /IrMn bilayers

Bulletin of the American Physical Society (2018)

Hilal Saglam J.-C. Rojas-Sánchez S. Petit M. Hehn Wei Zhang

Independence

Exchange bias

Orbit (dynamics)

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Excess velocity of magnetic domain walls close to the depinning field

Physical review. B./Physical review. B (2017)

Nirvana Caballero Iván Fernández Aguirre L. J. Albornoz Alejandro B. Kolton J.-C. Rojas-Sánchez

Magnetic field driven domain wall velocities in [Co/Ni] based multilayers thin films have been measured using polar magneto-optic Kerr effect microscopy. The low field results are shown to be consistent with the universal creep regime of domain wall motion, characterized by a stretched exponential growth of the velocity with the inverse of the applied field. Approaching the depinning field from below results in an unexpected excess velocity with respect to the creep law. We analyze these results using scaling theory to show that this speeding up of domain wall motion can be interpreted as due to the increase of the size of the deterministic relaxation close to the depinning transition. We propose a phenomenological model which allows to accurately fit the observed excess velocity and to obtain characteristic values for the depinning field $H_d$, the depinning temperature $T_d$, and the characteristic velocity scale $v_0$ for each sample.

Domain wall (magnetism)

Hysteresis

10.1103/physrevb.96.224422

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Citations (19)