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  1. Article ; Online: Accelerating ultrafast magnetization reversal by non-local spin transfer.

    Remy, Quentin / Hohlfeld, Julius / Vergès, Maxime / Le Guen, Yann / Gorchon, Jon / Malinowski, Grégory / Mangin, Stéphane / Hehn, Michel

    Nature communications

    2023  Volume 14, Issue 1, Page(s) 445

    Abstract: When exciting a magnetic material with a femtosecond laser pulse, the amplitude of magnetization is no longer constant and can decrease within a time scale comparable to the duration of the optical excitation. This ultrafast demagnetization can even ... ...

    Abstract When exciting a magnetic material with a femtosecond laser pulse, the amplitude of magnetization is no longer constant and can decrease within a time scale comparable to the duration of the optical excitation. This ultrafast demagnetization can even trigger an ultrafast, out of equilibrium, phase transition to a paramagnetic state. The reciprocal effect, namely an ultrafast remagnetization from the zero magnetization state, is a necessary ingredient to achieve a complete ultrafast reversal. However, the speed of remagnetization is limited by the universal critical slowing down which appears close to a phase transition. Here we demonstrate that magnetization can be reversed in a few hundreds of femtoseconds by overcoming the critical slowing down thanks to ultrafast spin cooling and spin heating mechanisms. We foresee that these results outline the potential of ultrafast spintronics for future ultrafast and energy efficient magnetic memory and storage devices. Furthermore, this should motivate further theoretical works in the field of femtosecond magnetization reversal.
    Language English
    Publishing date 2023-01-27
    Publishing country England
    Document type Journal Article
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-023-36164-1
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Picosecond spin-orbit torque-induced coherent magnetization switching in a ferromagnet.

    Polley, Debanjan / Pattabi, Akshay / Rastogi, Ashwin / Jhuria, Kaushalya / Diaz, Eva / Singh, Hanuman / Lemaitre, Aristide / Hehn, Michel / Gorchon, Jon / Bokor, Jeffrey

    Science advances

    2023  Volume 9, Issue 36, Page(s) eadh5562

    Abstract: Electrically controllable nonvolatile magnetic memories show great potential for the replacement of conventional semiconductor-based memory technologies. Here, we experimentally demonstrate ultrafast spin-orbit torque (SOT)-induced coherent magnetization ...

    Abstract Electrically controllable nonvolatile magnetic memories show great potential for the replacement of conventional semiconductor-based memory technologies. Here, we experimentally demonstrate ultrafast spin-orbit torque (SOT)-induced coherent magnetization switching dynamics in a ferromagnet. We use an ultrafast photoconducting switch and a coplanar strip line to generate and guide a ~9-picosecond electrical pulse into a heavy metal/ferromagnet multilayer to induce ultrafast SOT. We then use magneto-optical probing to investigate the magnetization dynamics with sub-picosecond resolution. Ultrafast heating by the approximately 9 picosecond current pulse induces a thermal anisotropy torque which, in combination with the damping-like torque, coherently rotates the magnetization to obtain zero-crossing of magnetization in ~70 picoseconds. A macro-magnetic simulation coupled with an ultrafast heating model agrees well with the experiment and suggests coherent magnetization switching without any incubation delay on an unprecedented time scale. Our work proposes a unique magnetization switching mechanism toward markedly increasing the writing speed of SOT magnetic random-access memory devices.
    Language English
    Publishing date 2023-09-06
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2810933-8
    ISSN 2375-2548 ; 2375-2548
    ISSN (online) 2375-2548
    ISSN 2375-2548
    DOI 10.1126/sciadv.adh5562
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Swept coded aperture real-time femtophotography.

    Liu, Jingdan / Marquez, Miguel / Lai, Yingming / Ibrahim, Heide / Légaré, Katherine / Lassonde, Philippe / Liu, Xianglei / Hehn, Michel / Mangin, Stéphane / Malinowski, Grégory / Li, Zhengyan / Légaré, François / Liang, Jinyang

    Nature communications

    2024  Volume 15, Issue 1, Page(s) 1589

    Abstract: Single-shot real-time femtophotography is indispensable for imaging ultrafast dynamics during their times of occurrence. Despite their advantages over conventional multi-shot approaches, existing techniques confront restricted imaging speed or degraded ... ...

    Abstract Single-shot real-time femtophotography is indispensable for imaging ultrafast dynamics during their times of occurrence. Despite their advantages over conventional multi-shot approaches, existing techniques confront restricted imaging speed or degraded data quality by the deployed optoelectronic devices and face challenges in the application scope and acquisition accuracy. They are also hindered by the limitations in the acquirable information imposed by the sensing models. Here, we overcome these challenges by developing swept coded aperture real-time femtophotography (SCARF). This computational imaging modality enables all-optical ultrafast sweeping of a static coded aperture during the recording of an ultrafast event, bringing full-sequence encoding of up to 156.3 THz to every pixel on a CCD camera. We demonstrate SCARF's single-shot ultrafast imaging ability at tunable frame rates and spatial scales in both reflection and transmission modes. Using SCARF, we image ultrafast absorption in a semiconductor and ultrafast demagnetization of a metal alloy.
    Language English
    Publishing date 2024-02-21
    Publishing country England
    Document type Journal Article
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-024-45820-z
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Sensing Mechanism of Surface Acoustic Wave Magnetic Field Sensors Based on Ferromagnetic Films.

    Yang, Yang / Mishra, Harshad / Han, Tao / Hage-Ali, Sami / Hehn, Michel / Elmazria, Omar

    IEEE transactions on ultrasonics, ferroelectrics, and frequency control

    2021  Volume 68, Issue 7, Page(s) 2566–2575

    Abstract: Surface acoustic wave (SAW) sensors with ferromagnetic materials are used to measure magnetic fields or electric currents. The magnetic field sensitivities of SAW magnetic field sensors are essentially influenced by various factors. The sensing mechanism ...

    Abstract Surface acoustic wave (SAW) sensors with ferromagnetic materials are used to measure magnetic fields or electric currents. The magnetic field sensitivities of SAW magnetic field sensors are essentially influenced by various factors. The sensing mechanism is complex due to the multiphysics coupling of the magnetic field, solid mechanics, and electric field. The magnetostriction effect, ∆E effect, and the third-order material constants are taken into consideration. The shape demagnetizing effect is reduced by increasing the length-to-width ratio and length-to-height ratio of a ferromagnetic film on an SAW resonator. The model is verified by experiments and accurately predicts the magnetic field sensitivities of SAW resonant magnetic field sensors. The factors affecting the sensitivities are investigated from the perspective of the sensing mechanism. A grooved sensing surface structure is explored for improved sensitivity. The results are beneficial to design reliable SAW magnetic field sensors with enhanced sensitivity.
    Language English
    Publishing date 2021-06-29
    Publishing country United States
    Document type Journal Article
    ISSN 1525-8955
    ISSN (online) 1525-8955
    DOI 10.1109/TUFFC.2021.3069382
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Book ; Online: Boosting room temperature tunnel magnetoresistance in hybrid magnetic tunnel junctions under electric bias

    González-Ruano, César / Tiusan, Coriolan / Hehn, Michel / Aliev, Farkhad G.

    2021  

    Abstract: Spin-resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel junctions (MTJs), providing room temperature functionality in modern spin electronics. However, the core ... ...

    Abstract Spin-resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel junctions (MTJs), providing room temperature functionality in modern spin electronics. However, the core process of the electron symmetry filtering breaks down under applied bias, dramatically reducing the TMR above 0.5 V. This strongly hampers the application range of MTJs. To circumvent the problem, resonant tunneling between ferromagnetic electrodes through quantum well states in thin layers has been used so far. This mechanism, however, is mainly effective at low temperatures. Here, a fundamentally different approach is demonstrated, providing a strong TMR boost under applied bias in V/MgO/Fe/MgO/Fe/Co hybrids. This pathway uses spin orbit coupling (SOC) controlled interfacial states in vanadium, which contrary to the V(001) bulk states are allowed to tunnel to Fe(001) at low biases. The experimentally observed strong increase of TMR with bias is modelled using two nonlinear resistances in series, with the low bias conductance of the first (V/MgO/Fe) element being boosted by the SOC-controlled interfacial states, while the conductance of the second (Fe/MgO/Fe) junctions controlled by the relative alignment of the two ferromagnetic layers. These results pave a way to unexplored and fundamentally different spintronic device schemes, with tunneling magnetoresistance uplifted under applied electric bias.

    Comment: Accepted for publication in Advanced Electronic Materials
    Keywords Condensed Matter - Mesoscale and Nanoscale Physics ; Condensed Matter - Materials Science
    Subject code 530
    Publishing date 2021-10-11
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  6. Article ; Online: Single-Shot Laser-Induced Switching of an Exchange Biased Antiferromagnet.

    Guo, Zongxia / Wang, Junlin / Malinowski, Gregory / Zhang, Boyu / Zhang, Wei / Wang, Hangtian / Lyu, Chen / Peng, Yi / Vallobra, Pierre / Xu, Yong / Xu, Yongbing / Jenkins, Sarah / Chantrell, Roy W / Evans, Richard F L / Mangin, Stéphane / Zhao, Weisheng / Hehn, Michel

    Advanced materials (Deerfield Beach, Fla.)

    2024  , Page(s) e2311643

    Abstract: Ultrafast manipulation of magnetic order has challenged the understanding of the fundamental and dynamic properties of magnetic materials. So far single-shot magnetic switching has been limited to ferrimagnetic alloys, multilayers, and designed ... ...

    Abstract Ultrafast manipulation of magnetic order has challenged the understanding of the fundamental and dynamic properties of magnetic materials. So far single-shot magnetic switching has been limited to ferrimagnetic alloys, multilayers, and designed ferromagnetic (FM) heterostructures. In FM/antiferromagnetic (AFM) bilayers, exchange bias (H
    Language English
    Publishing date 2024-02-26
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 1474949-X
    ISSN 1521-4095 ; 0935-9648
    ISSN (online) 1521-4095
    ISSN 0935-9648
    DOI 10.1002/adma.202311643
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Book ; Online: Uncovering the role of the light-induced reduction of the inter-atomic exchange in the ultrafast demagnetization of Fe, Co, and Ni

    Scheid, Philippe / Hohlfeld, Julius / Malinowski, Gregory / Bergman, Anders / Hehn, Michel / Zhang, Wei / Eriksson, Olle / Lebègue, Sébastien / Mangin, Stéphane

    2023  

    Abstract: Time resolved measurements of the linear magneto-optical Kerr rotation reveal that, in the {\it 3d} ferromagnets Fe, Co and Ni, the amplitude of the demagnetization increases linearly with the fluence of the light. We rationalize this phenomenon as being ...

    Abstract Time resolved measurements of the linear magneto-optical Kerr rotation reveal that, in the {\it 3d} ferromagnets Fe, Co and Ni, the amplitude of the demagnetization increases linearly with the fluence of the light. We rationalize this phenomenon as being linearly driven by the increase in temperature, the electron-phonon and electron-magnon scattering, and a reduction of the inter-atomic exchange. The amplitude of the latter phenomenon, which until the present study has been widely overlooked, is obtained through \textit{ab initio} density functional theory calculations, and is argued to be the principal source of demagnetization in Ni and Co, while still contributing largely in Fe.
    Keywords Condensed Matter - Materials Science ; Condensed Matter - Other Condensed Matter
    Publishing date 2023-01-03
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Article ; Online: Optical Creation of Skyrmions by Spin Reorientation Transition in Ferrimagnetic CoHo Alloys

    Zhang, Wei / Huang, Tian Xun / Hehn, Michel / Malinowski, Grégory / Verges, Maxime / Hohlfeld, Julius / Remy, Quentin / Lacour, Daniel / Wang, Xin Ran / Zhao, Guo Ping / Vallobra, Pierre / Xu, Yong / Mangin, Stéphane / Zhao, Wei Sheng

    ACS Applied Materials & Interfaces. 2023 Jan. 23, v. 15, no. 4 p.5608-5619

    2023  

    Abstract: Manipulating magnetic skyrmions by means of a femtosecond (fs) laser pulse has attracted great interest due to their promising applications in efficient information-storage devices with ultralow energy consumption. However, the mechanism underlying the ... ...

    Abstract Manipulating magnetic skyrmions by means of a femtosecond (fs) laser pulse has attracted great interest due to their promising applications in efficient information-storage devices with ultralow energy consumption. However, the mechanism underlying the creation of skyrmions induced by an fs laser is still lacking. As a result, a key challenge is to reveal the pathway for the massive reorientation of magnetization from trivial to nontrivial topological states. Here, we studied a series of ferrimagnetic CoHo alloys and investigated the effect of a single laser pulse on the magnetic states. Thanks to the time-resolved magneto-optical Kerr effect and imaging techniques, we demonstrate that the laser-induced phase transitions from single domains into a topological skyrmion phase are mediated by the transient in-plane magnetization state, in real time and space domains, respectively. Combining experiments and micromagnetic simulations, we propose a two-step process for creating skyrmions through laser pulse irradiation: (i) the electron temperature enhancement induces a spin reorientation transition on a picosecond (ps) timescale due to the suppression of perpendicular magnetic anisotropy (PMA) and (ii) the PMA slowly restores, accompanied by out-of-plane magnetization recovery, leading to the generation of skyrmions with the help of spin fluctuations. This work provides a route to control skyrmion patterns using an fs laser, thereby establishing the foundation for further exploration of topological magnetism at ultrafast timescales.
    Keywords anisotropy ; energy ; irradiation ; magnetism ; temperature ; topology ; ultrafast magnetism ; magnetic skyrmions ; spintronics ; time-resolved techniques ; magnetic phase transitions
    Language English
    Dates of publication 2023-0123
    Size p. 5608-5619.
    Publishing place American Chemical Society
    Document type Article ; Online
    ISSN 1944-8252
    DOI 10.1021/acsami.2c19411
    Database NAL-Catalogue (AGRICOLA)

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  9. Book ; Online: Magnetic SAW RFID Sensor Based on Love Wave for Detection of Magnetic Field and Temperature

    Mengue, Prince / Meistersheim, Laurine / Hage-Ali, Sami / Floer, Cécile / Petit-Watelot, Sébastien / Lacour, Daniel / Hehn, Michel / Elmazria, Omar

    2023  

    Abstract: Magnetic field measurement including a temperature compensation is essential for a magnetic field sensor. This study investigates a magnetic surface acoustic wave (MSAW) sensor in a reflective delay line configuration with two acoustic propagation paths ... ...

    Abstract Magnetic field measurement including a temperature compensation is essential for a magnetic field sensor. This study investigates a magnetic surface acoustic wave (MSAW) sensor in a reflective delay line configuration with two acoustic propagation paths with and without magnetic field sensitive layer. The delay in path with sensitive layer leads to magnetic field detection and the one without enable temperature measurement and thus compensation for the first path. The developed sensor is based on a ZnO/LiNbO$_3$ Ycut (X-direction) layered structure as Love wave platform. Love wave as a shear wave being more favorable for magnetic detection. Co-Fe-B is considered as sensitive layer to detect magnetic field changes and is deposited on the top of ZnO, but only on one of the two paths. We combined an original configuration of connected IDTs with a high electromechanical coupling coefficient (K$^2$) mode to improve the signal amplitude. The achieved sensor exhibits a high temperature and magnetic field sensitivity of -63 ppm/$^\circ$C and -781 ppm/mT, respectively. The temperature compensation method for magnetic field measurement is demonstrated using a differential measurement by subtracting the delay times obtained for the two paths with and without the sensitive layer. Finally, The sensor exhibited good repeatability at various temperatures. Moreover, the device developed allows in addition to the multisensor functionality, the radio frequency identification (RFID) which is necessary for the deployment of sensor networks.
    Keywords Electrical Engineering and Systems Science - Signal Processing
    Publishing date 2023-10-02
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  10. Book ; Online: Extending the scope and understanding of all-optical magnetization switching in Gd-based alloys by controlling the underlying temperature transients

    Verges, Maxime / Zhang, Wei / Remy, Quentin / Le-Guen, Yann / Gorchon, Jon / Malinowski, Gregory / Mangin, Stephane / Hehn, Michel / Hohlfeld, Julius

    2023  

    Abstract: We use the thickness of Cu layers to control all-optical switching of magnetization in adjacent Gd$_{24}$(Fe$_9$0Co$_{10}$)$_{76}$ films. While increasing the Cu thickness from 5 to 900nm has no effect on the switching threshold, it significantly ... ...

    Abstract We use the thickness of Cu layers to control all-optical switching of magnetization in adjacent Gd$_{24}$(Fe$_9$0Co$_{10}$)$_{76}$ films. While increasing the Cu thickness from 5 to 900nm has no effect on the switching threshold, it significantly enlarges the fluence and pulse duration at which multiple domains emerge. Having shown that thermally activated multi-domain formation limits the maximum fluence and pulse duration for controlled switching, we demonstrate that continuous magnetization reversal precedes multi-domain formation in Gd$_{18}$Dy$_4$Co$_{78}$ films excited with fluences slightly larger than the multi-domain threshold.
    Keywords Condensed Matter - Materials Science
    Publishing date 2023-09-26
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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