Laser-induced Creation of antiferromagnetic 180-degree domains in NiOPt bilayers Hendrik MeeryStephan WustzChristin SchmittyPaul HerrgenzFelix

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Laser-induced Creation of antiferromagnetic

180-degree domains in NiO/Pt bilayers

Hendrik Meer,∗,†Stephan Wust,‡Christin Schmitt,†Paul Herrgen,‡Felix

Fuhrmann,†Steﬀen Hirtle,‡Beatrice Bednarz,†Adithya Rajan,†Rafael Ramos,¶,∇

Miguel Angel Niño,§Michael Foerster,§Florian Kronast,kArmin Kleibert,⊥

Baerbel Rethfeld,‡Eiji Saitoh,¶,#,@,4Benjamin Stadtmüller,†,‡Martin

Aeschlimann,‡and Mathias Kläui∗,†

†Institute of Physics, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany

‡Department of Physics and Research Center OPTIMAS, Technische Universität

Kaiserslautern, 67663 Kaiserslautern, Germany

¶WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577,

Japan

§ALBA Synchrotron Light Facility, Carrer de la Llum 2-26, Cerdanyola del Vallés, 08290

Barcelona, Spain

kHelmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489

Berlin, Germany

⊥Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland

#Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan

@Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan

4Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan

∇Centro de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS),

Departamento de Química-Física, Universidade de Santiago de Compostela, Santiago de

Compostela 15782, Spain

E-mail: meer@uni-mainz.de; Klaeui@Uni-Mainz.de

arXiv:2210.11009v2 [cond-mat.mtrl-sci] 23 Mar 2023

Abstract

We demonstrate how the antiferromagnetic order in heterostructures of NiO/Pt

thin ﬁlms can be modiﬁed by optical pulses. We irradiate our samples with laser light

and identify an optically induced creation of antiferromagnetic domains by imaging

the created domain structure utilizing the X-ray magnetic linear dichroism eﬀect. We

study the eﬀect of diﬀerent laser polarizations on the domain formation and identify a

polarization-independent creation of 180◦domain walls and domains with 180◦diﬀer-

ent Nèel vector orientation. By varying the irradiation parameters, we determine the

switching mechanism to be thermally induced and demonstrate the reversibility. We

thus demonstrate experimentally the possibility to optically create antiferromagnetic

domains, an important step towards future functionalization of all optical switching

mechanisms in antiferromagnets.

Introduction

To overcome the limitations of ferromagnetic systems (FMs) it is a key step to transition

to antiferromagnetic systems (AFMs) in future spintronic devices. Due to their net mag-

netic moment FMs are limited in their bit packing density and stability against external

ﬁelds compared to antiferromagnets.1Another key advantage of antiferromagnets is their

potential for ultrafast applications due to their inherent dynamics with resonant frequencies

in the THz range.2Recently, the electrical switching of antiferromagnets has been intensely

investigated.3–5 However, to achieve switching on an ultrashort timescale, we must transition

from electrical to optical modiﬁcation of the antiferromagnetic order.

In ferri- and ferromagnetic material systems, fs-laser-induced all-optical switching (AOS)

has been intensively studied.6–9 Thermally induced switching has been observed in ferrimag-

netic GdFeCo alloys6,10 and all-optical helicity-dependent switching (AO-HDS) based on the

inverse Faraday eﬀect has been observed in a wide range of ferri- and ferromagnetic mate-

rials.11 For antiferromagnetic materials, studies on the all-optical switching have focused on

the excitation of magnon modes.12–15 There are experimental reports of large-scale optical

switching of antiferromagnetic order in the tilted antiferromagnet TbMnO3.16 However, the

underlying mechanism relies on the electric polarization and cannot be easily transferred

to other AFM systems. Theoretical studies predict possible optically induced switching

in antiferromagnetic NiO,17,18 NiO/FM bilayers19 and other collinear antiferromagnets.20

Recently, ﬁrst experimental evidence for light-induced manipulation of antiferromagnetic

domains in NiO crystals has been reported.21 NiO is a prototypical collinear insulating an-

tiferromagnetic system exhibiting promising features for future potential spintronic devices:

current-induced switching of the antiferromagnetic order,5,22 electrical readout,23 antifer-

romagnetic shape anisotropy,24 and ultrafast spin dynamics in the THz range.2,25,26 The

magnetic order of NiO thin ﬁlms can be temporarily modulated by irradiation with ultrafast

laser pulses,27 and several studies have reported helicity-dependent excitation of coherent

magnons in NiO.13,28 NiO exhibits a strong magnetoelastic coupling29 and thus the above-

mentioned optical manipulation of antiferromagnetic domains21 has been attributed to a

particular phononic mechanism.30 While several mechanisms have theoretically proposed

optically induced switching of NiO, there are no experimental reports on the light-induced

domain switching of the antiferromagnetic order in NiO thin ﬁlms.

Here, we investigate the domain structure of NiO/Pt bilayers using X-ray photo-emission

electron microscopy (XPEEM) with magnetic linear dichroism as the contrast mechanism,

that were irradiated by circularly and linearly polarized laser-light. We observe optically

induced changes of the domain structure. In contrast to often considered switching between

diﬀerent Néel vector axes, we observe the creation of 180◦domains and domain walls, in-

dependent of the laser polarization. Variation of the irradiation parameters allows us to

identify a thermal origin of the optically induced antiferromagnetic order. We demonstrate

the possibility to optically create antiferromagnetic domains in a prototypical antiferromag-

netic system.

Results

We prepared 10 nm thick NiO(001) thin ﬁlms that are epitaxially grown on MgO(001) sub-

strates by reactive magnetron sputtering. The ﬁlms are additionally capped with a 2 nm

thick platinum layer to allow for imaging with X-ray magnetic linear dichroism photoemis-

sion electron microscopy (XMLD-PEEM). We have previously characterized and investigated

similarly grown NiO(001) thin ﬁlms and observed that the strain from the substrate mis-

match leads to preferential out-of-plane alignment of the Néel vector in these thin ﬁlms,

stabilizing only one type of Spin-domains (S-domain).31–34 Therefore, only four diﬀerent

Twin-domains (T-domains) are present in our ﬁlms, each accompanied by a strong rhombo-

hedral distortion. Similar to our previous studies on 10 nm NiO thin ﬁlms,34 we observe a

domain structure in our ﬁeld of view (FOV) which predominantly consists of one T-domain.

To study the eﬀect of laser-irradiation on NiO/Pt bilayers, we use an ultrafast ampliﬁed

laser system with a central wavelength of 800 nm and with a pulse repetition rate of 1 kHz.

We irradiated our samples with pulse trains of diﬀerent pulse duration, pulse ﬂuences, il-

lumination time, and polarization. We imaged the antiferromagnetic domain structure of

the laser irradiated regions using energy dependent XMLD-PEEM at the double peak of the

Ni L2edge.35 Fig. 1 shows the antiferromagnetic domain structure of a region irradiated

with circularly right-polarized laser light. Several narrow domain walls (bright lines) can

be observed around the central laser spot. The XMLD contrast depends on the orientation

of the incoming electric ﬁeld and the orientation of the Néel vector. We varied the po-

larization of the incoming X-ray (ω= 90◦,112.5◦,135◦,157.5◦,0◦) and the azimuthal angle

(γ= 90◦,120◦,135◦,150◦,165◦,180◦) of the sample with respect to the incoming beam. For

all combinations of ωand γwe observe no diﬀerence in contrast between the domains inside

and outside the domain walls. The absence of contrast changes indicates that the projection

of the Néel vector in these domains onto the X-ray polarization is identical for all angles of ω

and γand points along the same directions.36 However, for diﬀerent combinations of ωand

γwe could observe variation and inversion of the contrast between the domain wall and the

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Laser-inducedCreationofantiferromagnetic180-degreedomainsinNiO/PtbilayersHendrikMeer,,yStephanWust,zChristinSchmitt,yPaulHerrgen,zFelixFuhrmann,ySteenHirtle,zBeatriceBednarz,yAdithyaRajan,yRafaelRamos,{,rMiguelAngelNiño,xMichaelFoerster,xFlorianKronast,kArminKleibert,?BaerbelRethfeld,zEijiSaitoh,{...

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Laser-induced Creation of antiferromagnetic 180-degree domains in NiOPt bilayers Hendrik MeeryStephan WustzChristin SchmittyPaul HerrgenzFelix

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