Route towards efficient magnetization reversal driven by voltage control of magnetic anisotropy (Scientific Reports - Nature, July 6th, 2021)


Abstract:   The voltage controlled magnetic anisotropy (VCMA) becomes a subject of major interest for spintronics due to its promising potential outcome: fast magnetization manipulation in magnetoresistive random access memories with enhanced storage density and very low power consumption. Using a macrospin approach, we carried out a thorough analysis of the role of the VCMA on the magnetization dynamics of nanostructures with out-of-plane magnetic anisotropy. Diagrams of the magnetization switching have been computed depending on the material and experiment parameters (surface anisotropy, Gilbert damping, duration/amplitude of electric and magnetic field pulses) thus allowing predictive sets of parameters for optimum switching experiments. Two characteristic times of the trajectory of the magnetization were analyzed analytically and numerically setting a lower limit for the duration of the pulses. An interesting switching regime has been identified where the precessional reversal of magnetization does not depend on the voltage pulse duration. This represents a promising path for the magnetization control by VCMA with enhanced versatility.

Collaboration: SPINTEC and University of Grenoble Alpes (Grenoble, France),
Technical University of Cluj-Napoca (Cluj-Napoca, Romania)

Funding: “EMERSPIN” grant ID PN-IIIP4-ID-PCE-2016-0143, No. UEFISCDI: 22/12.07.2017
and ”MODESKY” Grant ID PN-III-P4-ID-PCE-2020-0230 No. UEFISCDI: 4/04.01.2021.

Perpendicular Magnetic Anisotropy Electric Field Modulation in Magnetron-Sputtered Pt/Co/X/MgO Ultrathin Structures With Chemically Tailored Top Interface (IEEE Transactions on Magnetics, April 7th, 2021)


Abstract: Ab initio calculations of voltage-controlled perpendicular magnetic anisotropy predict that the adjunction of Pt at the top of Co/MgO interface in Pt/Co/MgO ultrathin structures would enhance the perpendicular anisotropy and its electric field ( E -field) variation rate. Following these theoretical expectations, using the magnetron-sputtering technique, we first designed and elaborated magnetic multilayered samples which have subsequently been patterned by UV lithography in magnetotransport devices. The as-deposited samples show perpendicular magnetization configuration whose E -field modulation has been studied by anomalous Hall effect magnetometry experiments under applied E -field in patterned devices. The measured voltage anisotropy modulation effect is found to be asymmetric with respect to the E -field polarity, in qualitative agreement with theoretical predictions.

Collaboration: SPINTEC and University of Grenoble Alpes (Grenoble, France),
Technical University of Cluj-Napoca (Cluj-Napoca, Romania)

Funding: “EMERSPIN” grant ID PN-IIIP4-ID-PCE-2016-0143, No. UEFISCDI: 22/12.07.2017
and ”MODESKY” Grant ID PN-III-P4-ID-PCE-2020-0230 No. UEFISCDI: 4/04.01.2021. 

Low‚ÄźEnergy Spin Precession in the Molecular Field of a Magnetic Thin Film (Annalen der Physik, February, 2021)


Abstract: Electronic spin precession and filtering are measured in the molecular field of magnetic thin films. Lab-on-chip experiments allow injection of electrons with energies between 0.8 and 1.1 eV, an energy range not yet explored in spin precession experiments. While filtering angles agree with previous reported values measured at much higher electron energies, spin precession angles of 2.5° in CoFe and 0.7° in Co per nanometer film thickness could be measured which are 30 times smaller than those previously measured at 7 eV. On the basis of ab initio calculations, the results are explained and it is shown that the band structure and layer roughness are playing a key role at low energy.


Collaboration: IJL and University of Lorraine (Nancy, France),
IPCMS and University of Strasbourg (Strasbourg, France),
SPINTEC and University of Grenoble Alpes (Grenoble, France)
 

Superconductivity-induced change in magnetic anisotropy in epitaxial ferromagnet-superconductor hybrids with spin-orbit interaction (Physical Review B, July 15th, 2020)


Abstract: The interaction between superconductivity and ferromagnetism in thin film superconductor/ferromagnet heterostructures is usually reflected by a change in superconductivity of the S layer set by the magnetic state of the F layers. Here we report the converse effect: transformation of the magnetocrystalline anisotropy of a single Fe(001) layer, and thus its preferred magnetization orientation, driven by the superconductivity of an underlying V layer through a spin-orbit coupled MgO interface. We attribute this to an additional contribution to the free energy of the ferromagnet arising from the controlled generation of triplet Cooper pairs, which depends on the relative angle between the exchange field of the ferromagnet and the spin-orbit field. This is fundamentally different from the commonly observed magnetic domain modification by Meissner screening or domain wall-vortex interaction, and it offers the ability to fundamentally tune magnetic anisotropies using superconductivity—a key step in designing future cryogenic magnetic memories.

Collaboration: MAGNETRANS and University of Madrid (Madrid, Spain),
IJL and University of Lorraine (Nancy, France),
Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology (Trondheim, Norway)
Department of Physics, Loughborough University (Loughborough , United Kingdom)

Funding: “EMERSPIN” grant ID PN-IIIP4-ID-PCE-2016-0143, No. UEFISCDI: 22/12.07.2017

Interfacial spin-orbit coupling: a platform for superconducting spintronics (Physical Review Applied, January 17th, 2020)

Abstract: Spin-orbit coupling (SOC) is a key interaction in spintronics, allowing electrical control of spin or magnetization and, vice versa, magnetic control of electrical current. However, recent advances have revealed much broader implications of SOC that is also central to the design of topological states with potential applications from low-energy dissipation and faster magnetization switching to high tolerance of disorder. SOC and the resulting emergent interfacial spin-orbit fields are simply realized in junctions through structural inversion asymmetry, while the anisotropy in magnetoresistance (MR) allows their experimental detection. Surprisingly, we demonstrate that an all-epitaxial ferromagnet/ Mg O /metal junction with a single ferromagnetic region and only negligible MR anisotropy undergoes a remarkable transformation below the superconducting transition temperature of the metal. The superconducting junction has a MR anisotropy 3 orders of magnitude higher and could enable novel applications in superconducting spintronics. In contrast to common realizations of MR effects that require a finite applied magnetic field, our system is designed to have two stable zero-field states with mutually orthogonal magnetizations: in plane and out of plane. This bistable magnetic anisotropy allows us to rule out orbital and vortex effects due to an applied magnetic field and identify the SOC origin of the observed MR. Such MR reaches approximately 20 % without an applied magnetic field and could be further increased for large magnetic fields that support vortices. Our findings call for a revisit of the role of SOC, even when it seems negligible in the normal state, and suggest an alternative platform for superconducting spintronics. 


Collaboration: MAGNETRANS and University of Madrid (Madrid, Spain)
IJL and University of Lorraine (Nancy, France)
Institute for Theoretical Physics, University of Regensburg, (Regensburg, Germany)
Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology (Cambridge, Massachusetts USA)
Department of Physics and Astronomy, Wayne State University, (Detroit, Michigan, USA)
Department of Physics, University at Buffalo, State University of New York, (Buffalo, New York , USA)

Funding: “EMERSPIN” grant ID PN-IIIP4-ID-PCE-2016-0143, No. UEFISCDI: 22/12.07.2017