{"id":54878,"date":"2022-09-23T08:59:33","date_gmt":"2022-09-23T06:59:33","guid":{"rendered":"https:\/\/www.iemn.fr\/articles-temporaires-anglais\/controle-facile-et-a-la-demande-de-la-polarisation-des-emetteurs-thz-spintroniques-2.html"},"modified":"2022-09-23T10:19:36","modified_gmt":"2022-09-23T08:19:36","slug":"controle-facile-et-a-la-demande-de-la-polarisation-des-emetteurs-thz-spintroniques-2","status":"publish","type":"post","link":"https:\/\/www.iemn.fr\/en\/newsletter\/controle-facile-et-a-la-demande-de-la-polarisation-des-emetteurs-thz-spintroniques-2.html","title":{"rendered":"Easy on-demand polarization control of spintronic THz emitters."},"content":{"rendered":"<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-av_heading-b6d0784086e144ef4ec98fa90d017b27\">\n#top .av-special-heading.av-av_heading-b6d0784086e144ef4ec98fa90d017b27{\npadding-bottom:10px;\n}\nbody .av-special-heading.av-av_heading-b6d0784086e144ef4ec98fa90d017b27 .av-special-heading-tag .heading-char{\nfont-size:25px;\n}\n.av-special-heading.av-av_heading-b6d0784086e144ef4ec98fa90d017b27 .av-subheading{\nfont-size:15px;\n}\n<\/style>\n<div  class='av-special-heading av-av_heading-b6d0784086e144ef4ec98fa90d017b27 av-special-heading-h2 blockquote modern-quote modern-centered  avia-builder-el-0  el_before_av_one_full  avia-builder-el-first'><h2 class='av-special-heading-tag'  itemprop=\"headline\"  >Easy on-demand polarization control of spintronic THz emitters.<\/h2><div class=\"special-heading-border\"><div class=\"special-heading-inner-border\"><\/div><\/div><\/div>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-p12l8y-92ee2226d13b9cc499344a0dc688ea35\">\n.flex_column.av-p12l8y-92ee2226d13b9cc499344a0dc688ea35{\nborder-radius:0px 0px 0px 0px;\npadding:0px 0px 0px 0px;\n}\n<\/style>\n<div  class='flex_column av-p12l8y-92ee2226d13b9cc499344a0dc688ea35 av_one_full  avia-builder-el-1  el_after_av_heading  el_before_av_one_half  first flex_column_div av-zero-column-padding'     ><section  class='av_textblock_section av-l8e4ocpk-dc733b940ea8e8a531766f60e63b32ff'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><blockquote>\n<p><strong><span style=\"color: #535f94;\">Ultra broadband emitters of terahertz radiation exploiting the dynamics of the spin (rather than the charge) of electrons in metallic spintronic multilayers, have in the last few years emerged on the research scene as flexible and robust THz sources with many properties unattainable by more conventional technologies. Especially unique is their ability of THz polarization switching through magnetization control of the ferromagnetic layer. At IEMN we have proven a very efficient way to set this magnetization direction (and therefore the emitted THz polarization) on demand without power loss at any chosen value over a full 2\u03c0 angle. Such a source can significantly improve applications in THz polarimetry and ellipsometry by avoiding the need for external polarizing elements. A fast control of this technique will furthermore allow to demonstrate modulated THz emitters at unprecedented speeds.<\/span><\/strong><\/p>\n<\/blockquote>\n<p><a href=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-54867 size-full aligncenter\" src=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_1.jpg\" alt=\"\" width=\"704\" height=\"405\" srcset=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_1.jpg 704w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_1-300x173.jpg 300w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_1-18x10.jpg 18w\" sizes=\"auto, (max-width: 704px) 100vw, 704px\" \/><\/a><\/p>\n<\/div><\/section><\/div>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-1aou08i-f3744de17155a2108d0bd01b12d363d7\">\n.flex_column.av-1aou08i-f3744de17155a2108d0bd01b12d363d7{\nborder-radius:0px 0px 0px 0px;\npadding:0px 0px 0px 0px;\n}\n<\/style>\n<div  class='flex_column av-1aou08i-f3744de17155a2108d0bd01b12d363d7 av_one_half  avia-builder-el-3  el_after_av_one_full  el_before_av_one_half  first flex_column_div av-zero-column-padding  column-top-margin'     ><section  class='av_textblock_section av-l8e4wxcg-06c2261ee4bbb4ebb4726f1f3e757796'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><h5>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d\">\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d{\ncolor:#7bb0e7;\nborder-color:#7bb0e7;\n}\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue871' data-av_iconfont='entypo-fontello' ><\/span><\/span><\/h5>\n<p><strong><span style=\"color: #535f94;\">THz technology has found applications that are nearing market implementation, such as nondestructive spectroscopy, chemical sensing and fast wireless communications.<\/span><\/strong> Control and flexible manipulation of the polarization state of a THz beam is in this context an important functionality that is still not straightforwardly realized. THz polarization states can be controlled by Fresnel-rhomb wave plates, wire-grid polarizers, birefringent wave plates, or active metamaterial-based devices. While these approaches are robust and can sometimes be actively controlled, they are most often either bulky or narrowband and present important insertion losses. <strong><span style=\"color: #535f94;\">Controlling the emitted polarization state directly upon generation is in this sense a more logical approach. This is precisely what the novel type of Inverse Spin Hall Effect THz emitters easily allow to achieve.<\/span><\/strong><\/p>\n<h5>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d\">\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d{\ncolor:#7bb0e7;\nborder-color:#7bb0e7;\n}\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue871' data-av_iconfont='entypo-fontello' ><\/span><\/span><\/h5>\n<p>Terahertz emission by spintronic effects was first demonstrated only about 5 years ago by the Kampfrath group at the Physics Department of the Freie Universit\u00e4t in Berlin. The emitter's configuration is nothing else but a thin-film metallic nanometric stack consisting of layers of a ferromagnetic metal (FM) and a normal metal (NM). After optical excitation of such a FM|NM heterostructure, an ultrafast spin current flows across the interface from the in-plane magnetized FM into the adjacent NM layer. This ultrafast out-of-plane spin current is then converted into an in-plane charge current through a spin-to-charge-current conversion (S2C) process. If the NM consists of a heavy metal like Pt, S2C predominantly happens by spin-orbit interactions in the NM layer by the inverse spin Hall effect (ISHE).<br \/>\nSimply stated ISHE will deviate a carrier current in a transverse direction depending on its spin state. Therefore if the carrier current is predominantly polarized in a certain state, this injected out-of-plane spin current will transform into a transverse charge current.<br \/>\nAnd since all involved physical processes (hot carrier excitation by IR pulses, diffusion and injection of spins, and relaxation and scattering in the NM) have characteristic time constants of the order of 10's of fs, the resulting transient charge current is in the sub-ps range and emits electromagnetic waves with THz frequencies. A remarkable and essential feature of the physics of the ISHE, is that the generated current is fundamentally always orthogonal to both the injected spin current and the spin polarization state !<br \/>\nTherefore controlling the magnetization direction of the spin injector (i.e. the FM layer), will directly determine the polarization state of the emitted radiation.<\/p>\n<\/div><\/section><\/div>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qo6xma-ba543f82684dca871c555403d13e60bf\">\n.flex_column.av-qo6xma-ba543f82684dca871c555403d13e60bf{\nborder-radius:0px 0px 0px 0px;\npadding:0px 0px 0px 0px;\n}\n<\/style>\n<div  class='flex_column av-qo6xma-ba543f82684dca871c555403d13e60bf av_one_half  avia-builder-el-7  el_after_av_one_half  el_before_av_one_full  flex_column_div av-zero-column-padding  column-top-margin'     ><section  class='av_textblock_section av-l8e4x2jk-46c908218a551134a6946a83efe7adaf'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><h5>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d\">\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d{\ncolor:#7bb0e7;\nborder-color:#7bb0e7;\n}\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue871' data-av_iconfont='entypo-fontello' ><\/span><\/span><\/h5>\n<p><strong><span style=\"color: #535f94;\">In the framework of a FET Open project (s-NEBULA FET Open Grant No. 863155 2020-2023,<br \/>\nhttps:\/\/s-nebula.eu), IEMN is partnering with leading French, German, Swedish and Czech research groups studying this new THz spintronic technology. The THz photonics team and the AIMAN-FILMS team are jointly leading the WP on improving the source functionalities of the demonstrated spintronic configurations. A specific expertise that we are bringing to this project is the development of engineered ferromagnetic multilayers with specific magnetic properties.<\/span><\/strong> Up till now spintronic THz emitters (STE) have used isotropic soft magnetic materials as spin injectors, more specifically CoFeB alloys. These ferromagnets have the advantage of being easily saturated in any in-plane direction by setting a weak external magnetic bias field in the desired direction. In view of the above, CoFeB-based STE's can thus generate a wanted THz polarization by appropriately turning the magnetic bias field to desired direction. Such a \"mechanical\" setting of the polarization is not only cumbersome but can moreover hardly be expected to allow fast control of the magnetization.<br \/>\nIn magnetism it is known that if a strong uniaxial anisotropy is created within a FM the alignment of the magnetization of a single domain of such a material will be the result of an energy balance between the anisotropy axis and the direction of the external magnetic bias. This results in the so-called Stoner-Wohlfarth mechanism. This predicts that the magnetization of the domain will rotate uniformly over a full circle by only applying an external field perpendicularly to the anisotropy axis. Such a layer used in a STE would thus allow a very efficient control of the THz polarization direction ! The polarization direction would be set by the value of a fixed magnetic field without needing to change its orientation.<\/p>\n<h5>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d\">\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d{\ncolor:#7bb0e7;\nborder-color:#7bb0e7;\n}\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue871' data-av_iconfont='entypo-fontello' ><\/span><\/span><\/h5>\n<p><strong><span style=\"color: #535f94;\">This is precisely what researchers of the AIMAIN-FILMS and THz Photonics group have achieved. Specifically they have demonstrated that a carefully chosen thin film multilayer combination of soft magnetic FeCo alloy with hard magnetic TbCo alloy, creates an effective ferromagnetic stack that has a pronounced uniaxial behaviour needing only limited strengths of magnetic bias to achieve full 360\u00b0 Stoner-Wohlfart rotation.<\/span><\/strong> From a magnetic point of view this was not a surprising result. The true impact of this work lies in the demonstration that such a layer achieves the same efficiency as a \"classical\" CoFeB layer when used in a spintronic THz emitter. <strong><span style=\"color: #535f94;\">Experiments have shown that using such an engineered multilayer leads to nearly as powerful THz signals as with optimised CoFeB alloys. On top of that, we have shown that this strength is maintained over the whole Stoner-Wohlfart polarization rotation cycle by sweeping an external magnetic bias along a single axis between values as low as 100 Oe (or 10mT).<\/span><\/strong><\/p>\n<\/div><\/section><\/div>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qfx0b6-4bd96b7010e06d18bd1465921e7145cc\">\n.flex_column.av-qfx0b6-4bd96b7010e06d18bd1465921e7145cc{\nborder-radius:0px 0px 0px 0px;\npadding:0px 0px 0px 0px;\n}\n<\/style>\n<div  class='flex_column av-qfx0b6-4bd96b7010e06d18bd1465921e7145cc av_one_full  avia-builder-el-11  el_after_av_one_half  avia-builder-el-last  first flex_column_div av-zero-column-padding  column-top-margin'     ><section  class='av_textblock_section av-l8e6mgx8-4c1d4f89436c3c4640b3d760c842132d'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><p><a href=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-54874 size-full\" src=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3.jpg\" alt=\"\" width=\"999\" height=\"624\" srcset=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3.jpg 999w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3-300x187.jpg 300w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3-768x480.jpg 768w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3-18x12.jpg 18w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2022\/09\/visuel_polarisation_3-705x440.jpg 705w\" sizes=\"auto, (max-width: 999px) 100vw, 999px\" \/><\/a><\/p>\n<h5>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d\">\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d{\ncolor:#7bb0e7;\nborder-color:#7bb0e7;\n}\n.av_font_icon.av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-qawvnx-2cc1ded53511b6d8e415ea06c66e9a4d avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue871' data-av_iconfont='entypo-fontello' ><\/span><\/span><\/h5>\n<p><strong><span style=\"color: #535f94;\">This quasistatic setting of the THz polarization direction of a STE has a profound impact on the usability of these emitters. One can now imagine a STE integrated with a tiny single-axis electromagnet that will emit a certain THz polarization by \"just\" setting the current of the electromagnet to the desired value.\u00a0<\/span><\/strong>\u00a0\u00a0In other words, an efficient broadband THz polarimetric source becomes a reality. The impact of the easy polarization control of this emitter type has several other far-reaching applications.<br \/>\nIn this work the Stoner-Wohlfarth type magnetization control was mainly quasistatically exploited. Dynamic fast control of the reversible magnetization is imaginable by operating the uniaxial anisotropic emitter near the spin reorientation transition (SRT), where the magnetization along the easy axis moves unhindered by an energy barrier under small amplitude RF excitations. Modulation speeds well beyond 10MHz are expected. Such a wideband fast-modulated STE with near 100% modulation index is a missing component for wireless THz datacom but could also find use in low-noise modulation ellipsometric THz spectroscopy. Furthermore, by cascading such emitters and exploiting the full 360\u00b0polarization control, any chosen elliptical THz polarization state can be created at will if a precise phase control between both cascaded emitters is implemented.<\/p>\n<p>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-qawvnx-6099b9ea98fff94dd4e4a46a58fb2c27\">\n.av_font_icon.av-qawvnx-6099b9ea98fff94dd4e4a46a58fb2c27{\ncolor:#7bb0e7;\nborder-color:#7bb0e7;\n}\n.av_font_icon.av-qawvnx-6099b9ea98fff94dd4e4a46a58fb2c27 .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-qawvnx-6099b9ea98fff94dd4e4a46a58fb2c27 avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue826' data-av_iconfont='entypo-fontello' ><\/span><\/span>Read more about this work in the ACS Photonics paper \"360\u00b0Polarization Control of Terahertz Spintronic Emitters UsingUniaxial FeCo\/TbCo2\/FeCo Trilayers\" (doi: <a href=\"https:\/\/doi.org\/10.1021\/acsphotonics.1c01782\" target=\"_blank\" rel=\"noopener\">https:\/\/doi.org\/10.1021\/acsphotonics.1c01782<\/a>) and on the FET Open project on <a href=\"https:\/\/s-nebula.eu\" target=\"_blank\" rel=\"noopener\">https:\/\/s-nebula.eu<\/a><\/p>\n<p><div  class='avia-button-wrap av-rpqvoq-0ccce5ff1512e3d1872824db20eed7c8-wrap avia-button-left  avia-builder-el-15  el_after_av_font_icon  el_before_av_button'><a href='mailto:mathias.vanwolleghem@univ-lille.fr'  class='avia-button av-rpqvoq-0ccce5ff1512e3d1872824db20eed7c8 av-link-btn avia-icon_select-yes-left-icon avia-size-small avia-position-left avia-color-silver'   aria-label=\"mathias.vanwolleghem@univ-lille.fr\"><span class='avia_button_icon avia_button_icon_left' aria-hidden='true' data-av_icon='\ue805' data-av_iconfont='entypo-fontello'><\/span><span class='avia_iconbox_title' >mathias.vanwolleghem@univ-lille.fr<\/span><\/a><\/div> \u00a0 <div  class='avia-button-wrap av-rpqvoq-29f0a73c21db3f35fddf7230dbe3c0ec-wrap avia-button-left  avia-builder-el-16  el_after_av_button  avia-builder-el-last'><a href='mailto:nicolas.tiercelin@iemn.fr'  class='avia-button av-rpqvoq-29f0a73c21db3f35fddf7230dbe3c0ec av-link-btn avia-icon_select-yes-left-icon avia-size-small avia-position-left avia-color-silver'   aria-label=\"nicolas.tiercelin@iemn.fr\"><span class='avia_button_icon avia_button_icon_left' aria-hidden='true' data-av_icon='\ue805' data-av_iconfont='entypo-fontello'><\/span><span class='avia_iconbox_title' >nicolas.tiercelin@iemn.fr<\/span><\/a><\/div><\/p>\n<\/div><\/section><\/div><\/p>","protected":false},"excerpt":{"rendered":"","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[297],"tags":[],"class_list":["post-54878","post","type-post","status-publish","format-standard","hentry","category-newsletter"],"_links":{"self":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/54878","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/comments?post=54878"}],"version-history":[{"count":0,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/54878\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/media?parent=54878"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/categories?post=54878"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/tags?post=54878"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}