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The race to save space, time and energy in technology products is driving a heavy research on solid state physics. One the one hand, it requires the reduction of the lateral sizes of electronic and mechanical systems to nanometric sizes where the electromagnetic effects of matter combine with the quantum effects. On the other hand, new bulk and interface phenomena have been discovered and implemented in natural or artificial nanomaterials.  In the field of magnetism, the magnetic memory (hard disk drive, MRAM), magnetic sensor and more generally Information Technology industries are particularly at the forefront in the development of atomically designed systems where information can be addressed at time scale down to femtosecond scale and always seek for new functionalities.   

               Asymmetric control of the atomic magnetic moment when applying a mechanical strain, so called piezomagnetism effect, has been predicted theoretically both for anti-ferromagnetic and ferromagnetic materials [1]. This effect is the counterpart of piezoelectricity in the theory of electrostatics.

Nevertheless, so far, it has been only observed in non-usual anti-ferromagnetic materials, like UO2 [2]. Very recently, our “SPIN” research group (https://spin.ijl.cnrs.fr), in collaboration with colleagues from MIT in Boston, made a fundamental discovery in this field. We have observed that the passage of an acoustic wave through a single crystal ferromagnetic thin film generates a variation in magnetic moment that does depend on the strain sign but does not depend on the direction of the magnetic moment, i.e. a piezomagnetic effect [3]          

                To date, we have observed this phenomenon on Co/Ni multilayer thin films where the thickness of Co and Ni are of the order or one to few atomic layers. During the internship then the thesis, we wish to carry out the same measurements for new samples by varying the thicknesses of the Cobalt and Nickel layers, in order to build a theoretical model for the appearance of piezomagnetism, to disentangle interface and bulk effects, and to be able to predict and test other piezomagnets. We also wish to carry out other complementary experiments (in our lab and in synchrotron) in order to characterize and understand the phenomenon on the timescale of the femtosecond up to the quasi-static state.

               The internship and phD thesis will be held at Institut Jean Lamour (IJL, https://ijl.univ-lorraine.fr), one of the largest European laboratories in the field of materials. It is located on the ARTEM site in the city center of Nancy. At IJL, around 50 researchers and students work in the field of magnetism from the atomic scale to applications.

              

[1] A.S. Borovik-Romanov et al. Magnetic properties, International Tables for Crystallography Vol. D 1.5, 105-149 (2006).

[2] M. Jaime et al. Nature communication 8, 99 (2017)

[3] T. Pezeril, T Hauet et al., submitted to Nature Materials (2020)

 

 

Contacts:

Thomas Hauet (thomas.hauet@univ-lorraine.fr)

Karine Dumesnil (karine.Dumesnil@univ-lorraine.fr)

Today, the study of the Spin Hall Effect (SHE) and its reciprocal effect, the Inverse Spin Hall Effect (ISHE), combined with the Spin-Orbit Torque (SOT), represents a major challenge in solid-state physics from the point of view of fundamental research and for future applications such as magnetic memories (MRAM)[1].

SOT-SHE consists in generating a pure spin current Js, i. e. without any net displacement of electrical charges, in a heavy non-magnetic metal (HM), such as Platinum, and injecting it into a ferromagnetic material (FM) to control its magnetization. To create this spin current Js, one method consists injecting an electric current Jc (charge current) in the heavy metal (HM) which must have a high Spin-Orbit Coupling coefficient. The Spin-Orbit Coupling will deflect electrons in opposite directions depending on their Spin, which corresponds to the Spin Hall Effect (SHE). For a given sign of Jc, it therefore results in a transverse pure spin current Js with an associated spin direction. By depositing a thin layer of this HM material on top of a ferromagnetic material (FM), part of the spin current Js is injected into the latter, causing a torque on its magnetization. If the sign of Jc injected into HM is reversed, the torque produced on the FM magnetization will be opposite. It is therefore possible to electrically control the magnetization dynamics of a ferromagnetic material in a structure consisting of the stacking of a thin HM layer on or under a thin FM layer (HM/FM structure).

So far, switching the magnetization of a system via Spin-Orbit Torque has been demonstrated with pulses down to 0.2 nanoseconds in duration [2]. This was considered as “ultrafast” at the time, and switching with shorter pulses was considered impractical. However, recently, we were able to demonstrate switching via Spin-Orbit Torques, using a mere 6 picoseconds electrical current pulse (10-12 seconds) [3]. To this aim, instead of using common commercial current pulse generators that are limited in bandwidth, we built a unique femtosecond laser platform with ultrafast optoelectronic switches, that allow for high intensity few picosecond electrical pulse generation. This achievement poses many new questions and provide us with a new method of study of spin-orbit torques close to various fundamental timescales.

The objective of the internship we propose is to study a number of different samples with our ultrafast current pulse platform, and to benchmark the results and compare them with slow switching experiments.

During the internship, the student will learn how to work around a femtosecond laser setup and generate ultrashort pulses and will be taught the basics of high-frequency electronics and spintronics. The student will need to systematically test different samples under different experimental conditions for switching via spin-orbit torques. The student will likely perform low frequency studies to characterize the spin-orbit torques, which will be useful to compare with the high speed results.

This work will likely result in a PhD. Therefore, working on the internship will be a strong plus for applying to the PhD position. We note that we have a strong collaboration with the Universities of California Berkeley and Riverside on this topic, and the student might have a chance to travel there during the PhD.

References

[1] Y. Niimi and Y. Otani, Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review, Rep. Prog. Phys. 78, 124501 (2015).

[2] Garello, K. et al. Ultrafast magnetization switching by spin-orbit torques. Appl. Phys. Lett. 105, 212402 (2014).

[3] Jhuria K. et al. Picosecond spin-orbit torque switching, Accepted in Nature Electronics. arXiv:1912.01377

Contacts:

Jon Gorchon

Spin Orbit Toque (SOT) is a promising technique to induce magnetization switching with high switching speed and low energy. However, there is a serious limitations for SOT switching driven by the spin Hall effect. In usual geometry, an in-plane magnetic field needs to be applied to induce some symmetry-breaking and obtain full magnetization reversal.

In the past we have studied SOT switching in ferrimagnetic materials like TbCo as sketched in the figure below. In this project we wish to study other ferrimagnetic material such as GdCo, DyCo and heterostructures as GdCo/TbCo or GdCo/DyCo

During the internship the candidate will grow the ferrimagnetic materials. The structural and magnetic properties of the multilayers will be characterized. Following previous study (1) we will study the possibility to manipulate magnetization using SOT without any applied magnetic field

This project aims at joining the expertise of one group at the Center for Quantum Phenomena; New York University and one group at Institut Jean Lamour in Université de Lorraine. During the internship the candidate will work at both institutions.

  • Thermal contribution to the Spin-Orbit torque in Metallic Ferrimagnetic systems, Thai Ha Pham, Soong-Geun Je, Pierre Vallobra, T. Fache D. Lacour,  Marie-Claire Cyrille, Gilles Gaudin, Olivier Boulle, Michel Hehn, J-C Rojas-Sánchez, Stéphane Mangin, Rev. Appl. 9, 034028 (2018)

 

 

Contacts:

Pr. Andrew Kent: Center for Quantum Phenomena; New York University https://as.nyu.edu/content/nyu-as/as/faculty/andrew-d-kent.html

Pr. Stéphane Mangin stephane.mangin@univ-lorraine.fr : Institut Jean Lamour, Université de Lorraine, https://spin.ijl.cnrs.fr

In recent years, there has been significant interest in exploiting the unique properties of magnetic domain walls and skyrmions in next-generation magnetic data storage, nonvolatile memories, and computation schemes. Skyrmions are particularly attractive, given their efficient motion in response to the spin-transfer and spin-orbit torques that can arise when an electrical current is passed through a sample. Skyrmions may form in ferromagnetic materials that feature competition between the noncollinear Dzyaloshinskii- Moriya interaction (DMI) and conventional ferromagnetic exchange. One approach to achieving this competition is by sandwiching thin ferromagnetic (FM) layers between heavy metal layers with large spin-orbit coupling (SOC), where an interfacial DMI can develop when there is an asymmetry between the sign or strength of DMI at the top and bottom interfaces of the magnetic layers. As the DMI strength is sensitive to the degree of SOC present at each FM interface, the DMI can be tuned by modifying the deposition conditions or chemical identity of the high-SOC layers

During the internship the candidate will grow magnetic multilayers where skyrmion can be created. The structural and magnetic properties of the multilayers will be characterized. Following previous studies (1,2) we will study nucleating skyrmions using short current pulse and ultra-short laser pulse

This project aims at joining the expertise of one group at Center for Memory and Recording Research in University California San Diego, and one group at Institut Jean Lamour in Université de Lorraine. During the internship the candidate will work at both institutions.

(1) Current-induced generation of skyrmions in Pt/Co/Os/Pt thin films, J. A. Brock, P. Vallobra, R.D. Tolley, S.A. Montoya, S. Mangin, E.E. Fullerton, Phys. Rev. B 102 2 024443 (2020)

(2) Creation of magnetic skyrmion Buble Lattices by Ultrafast laser in Ultrathin Films, S. -G. Je, P. Vallobra, T. Srivastava, J. -C. Rojas-Sánchez, T. H. Pham, M. Hehn, G. Malinowski, C. Baraduc, S. Auffret, G. Gaudin, S. Mangin, H. Béa, and O. Boulle, Nano Letters 18, 7362  (2018)

 

Contacts:

Pr Eric E Fullerton, efullerton@ucsd.edu Center for Memory and Recording Research; University California San Diego https://cmrr.ucsd.edu/research/faculty-profiles/fullerton.html

Pr. Stéphane Mangin stephane.mangin@univ-lorraine.fr : Institut Jean Lamour, Université de Lorraine, https://spin.ijl.cnrs.fr

Ultrafast spin electronics is an emerging field of research that combines the ideas and concepts of magneto-optics and opto-magnetism with spin transport phenomena, supplemented with the possibilities offered by photonics for ultrafast low-dissipative manipulation and transport of information. Both light and spin currents can control magnetic order, though the mechanisms as well as the corresponding time scales and energy dissipations differ. The project aims at the best of both worlds, combining short time scales and non-dissipative propagation of light pulses with nanoscale selectivity and strong interactions of spin currents, to create novel concepts for data technology. The ultimate goals are the creation and implementation of non-volatile, low-dissipative, and ultrafast functional elements.

During the internship the candidate will grow Magnetic Tunnel Junction (MTJ) and characterize their structural and magnetic properties. The magnetization of the magnetic layers of the MTJ will then be manipulated using magnetic field or/and femto-second laser pulses

This project aims at joining the expertise of one at the Research Institut of Electrical Communication in Tohoku University, and one group at institut Jean Lamour in Université de Lorraine. During the internship the candidate will work at both institutions.

Contacts:

Pr. Stéphane Mangin stephane.mangin@univ-lorraine.fr

Institut Jean Lamour,  Université
de Lorraine,
https://spin.ijl.cnrs.fr

Pr Shunsuke Fukami

Research Institut of Electrical Communication,
Tohoku University http://www.spin.riec.tohoku.ac.jp/en/

The digital data generated annually around the world is now counted in zettabytes, or trillions of billions of bytes. This is equivalent to delivering hundreds of millions of books of data every second. The amount of data generated continues to grow because of the developpement of “Internet of Things”, “Autonomous Driving” , “ Artificial Intelligence” etc … . Its growth is so strong that if the same technologies continued to be used, by 2040 all of the current global electricity consumption would be devoted to data storage.

Spin-based rather than charge-based logic is in principle faster and more energy efficient, which might offer a solution to the handling of the exponential increase in data traffic. Superconductivity, on the other hand, allows zero-dissipation charge transport and the introduction of superconducting circuitry might considerably reduce the energy load associated to data traffic.  Recent theoretical and experimental works have shown that the introduction of superconducting elements in spin-based devices can significantly boost their performance for logic operation. One example of how superconducting order can enhance conventional spintronics is in the superconducting analogue of a giant magnetoresistance junction. The substitution of the metallic spacer between the two ferromagnets with a superconductor has been shown to lead to potentially much higher resistance changes. Moreover, quasiparticles in the superconducting state have been shown to have spin relaxation times that exceed those of normal metals by several orders of magnitude, in principle allowing for much more effective spin transport.

This project aims at joining the expertise of two groups at Cavendish laboratory  in Cambridge University, and one group at institut Jean Lamour in Université de Lorraine to investigate how spin transport in superconducting spintronic heterostructures scale in the picosecond regime, comparable to the relaxation times of quasiparticles. Previous experiments have broadly focused on the DC limit whereas the experiments that we propose here are very timely and essential for accessing the potential for the implementation of ultra-fast device functionalities.

Contacts:

Pr. Stéphane Mangin stephane.mangin@univ-lorraine.fr :

Institut Jean Lamour,  Université de Lorraine, https://spin.ijl.cnrs.fr

Pr Jason Robinson

Cavendish Laboratory, Cambridge University https://www.robinson.msm.cam.ac.uk

Dr Chiara Ciccarelli

Cavendish Laboratory, Cambridge University  https://www.ciccarelli.phy.cam.ac.uk