Olivier FRUCHART Univ. Grenoble Alpes / CEA / CNRS, SPINTEC, France - PowerPoint PPT Presentation

Olivier FRUCHART Univ. Grenoble Alpes / CEA / CNRS, SPINTEC, France

Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Quizz #0 Dipolar energy is positive Dipolar energy results Dipole-dipole energy may from dipole-dipole energy be negative ℰ d = 1 𝟑 d𝒲 2 𝜈 0 ම 𝐈 d 𝒲 ℰ = −2 𝜈 0 𝜈 1 𝜈 2 4𝜌𝑠 3 Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Quizz #1 ℰ = −2 𝜈 0 𝜈 1 𝜈 2 4𝜌𝑠 3 ℰ = + 𝜈 0 𝜈 1 𝜈 2 4𝜌𝑠 3 Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Quizz #2 Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Magnetic domains Magnetic length scales 2 𝐹 = 𝐵 𝜖𝑛 𝑗 Numerous and complex shape of domains + 𝐿 sin 2 𝜄 𝜖𝑦 𝑘 Exchange Anisotropy J/m 3 J/m Anisotropy exchange length Δu = 𝐵/𝐿 1 nm → 100 nm Hard Soft History: Weiss domains Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Versatility Imaging speed Samples made with lithography or ex situ OK ? Sample preparation needed ? Need for sample preparation ? How much time for one image ? Compatible with various environments ? (temperature, field etc.) Access What is probed Large-scale instrument or in-lab ? Surface or volume technique ? Expensive or cheap ? Sensitivity ? Magnetization, stray field, other ? No No univ iversal tech echnique Many cri criteria to to be be bala lanced Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

1982 : inventing the scanning tunneling microscope G. Binnig, H. Rohrer, C. Gerber & E. Weibel Tunneling through a controllable vacuum gap Appl. Phys. Lett. 40, 178 (1982) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

1982 : inventing the scanning tunneling microscope G. Binnig, H. Rohrer, C. Gerber & E. Weibel Tunneling through a controllable vacuum gap Appl. Phys. Lett. 40, 178 (1982) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

https://www.nobelprize.org Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

High resolution and sensitivity Topography – Large scale Self-organized growth of magnetic dots (Co) 350 x 350 nm 100 x 100 nm O. Fruchart et al., Phys. Rev. Lett. 23 (14), 2769 (1999) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

High resolution and sensitivity Spectroscopy → Elemental information Dots embedded in Au matrix TOPOGRAPHY SPECTROSCOPY 100 x 100 nm Au dI/dV (nA/V) 2 Co 1 0 -0.8 -0.4 0 0.4 0.8 Sample voltage (V) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Mapping surface quantum well states Atom manipulation Fe atoms on Copper, low temperature Xe atoms, low temperature D. Eigler, Nature (1990) For magnetism: H. Oka et al., Spin-polarized quantum confinement in nanostructures: Scanning tunneling microscopy, Rev. Mod. Phys. 86, 1127- 1168 (2014) http://research.physics.berkeley.edu/crommie Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Same principle as tunneling magnetoresistance (TMR) in the solid state Spectroscopic principle Courtesy: W. Wulfhekel Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

First hints: apparent height of AF Spectroscopy: the Cr(001) surface atomic steps on Cr(001) Fe-coated W tip CrO2 tip 100nm R. Wiesendanger et al., Phys. Rev. Lett. 65, 247 (1990) M. Kleibert et al., Phys. Rev. Lett. 85, 4606 (2000) R. Wiesendanger et al., Rev. Mod. Phys. 81, 1495 (2009) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Modulation technique (deprecated) ac modulation of magnetization of soft bulk tip Co(0001) – Micro-domain wall Lock-in detection of tunneling current H. Ding at al., Europhys. Lett. 57, 100 (2002) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Antiferromagnetic Fe/W(001) Current-assisted switching Skyrmions, write & delete One monolayer Fe 1ML Fe(110)/W(110) M. Bode et al., Nat. Mater. 5, S. Krause et al., Science 317, N. Romming et al., Science 477-481 (2006) 1537 (2007) 341, 636 (2013) R. Wiesendanger et al., Rev. Mod. Phys. 81, 1495 (2009) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Principle Au[2.2nm]/Fe[1]/Au[ 2.6]/Fe[1.6]/GaAs Assets Sen Sensitive to to transport High contrast Hig Hig High spa spatial reso esolu lution (5-10 10 nm nm?) Not ot so so ver ersatil ile P. Turban, H. Marie, Rennes Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Key elements of an Atomic Force Microscope (AFM) Probing Mechanical force -> Topography, tribology ( adhesion etc.) Magnetic force -> magnetic domains Electric forces -> ferroelectric domains, semiconductor memory cells etc. Detecting Laser deflection / interference Capacitance G. Binnig et al., Phys. Rev. Lett. 56, 930-933 (1986) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Mechanical excitation of cantilevers Amplitude Inertia Damping Spring External force Dephasing Notations Seek solutions for Reference angular velocity Quality factor Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Tip-sample interaction treated as perturbation 𝑛 ሷ 𝑨 + Γ ሶ 𝑨 + 𝑙𝑨 = 𝐺 𝑨 (𝑨) with 𝐺 𝑨 𝑨 = 𝐺 𝑨 0 + 𝑨 − 𝑨 0 𝜖 𝑨 𝐺 𝑨 Mere renormalization: Phase shift Attractive force Red shift 𝜀𝜒 = − 𝑅 𝑙 𝜖 𝑨 𝐺 𝑨 Forces monitored Repulsive force th through phase e shift ift Blue shift Not otice my con onven ention : dec ecreasin ing phase Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

First report : Y. Martin et al., Appl. Phys. Lett. 50, 1455 (1987) R. Proksch et al., Modern techniques for characterizing Review : magnetic materials, Springer, p.411 (2005) Two-pass technique Topography Magnetism Fe dot (25nm), 2.5x1 microns Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Tip is a monopole Tip is a dipole 𝐹 1,2 = −𝜈 0 𝜈 2 . 𝐼 d 𝐹 1,2 = 𝜈 0 𝜏. 𝜚 𝐺 𝑨 = −𝜈 0 𝜏𝐼 d ,𝑨 𝐹 1,2 = −𝜈 0 𝜈 𝑦 . 𝐼 d ,𝑦 + 𝜈 𝑧 . 𝐼 d ,𝑧 + 𝜈 𝑨 . 𝐼 d ,𝑨 𝜀𝜒 = 𝑅 𝜀𝜒 = 𝑅 2 𝐼 d ,𝑗 𝑙 𝜈 0 𝜈 𝑗 𝜖 𝑨 𝑙 𝜈 0 𝜏𝜖 𝑨 𝐼 d ,𝑨 In In practice, a com ombin ination of of both oth mod odel els is is bes est suit ited ed (d (dip ipole le is is more im important) t) MFM is is sen ensit itiv ive to to som ome deri erivative( e(s) of of th the str tray field field fr from th the sample le Quantitative analysis, see e.g.: H. Hug, J. Appl. Phys. 83, 5609 (1998) and followers Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Ultimate spatial resolution: 20nm ? Definition-depen enden ent: FWHM, variance, 85 85% etc. 1x1 µm Make statis istic ics: ob obje ject, ori orientati tion etc. FePt, epitaxial (4nm) Advan anced: modelin ing, dec econvoluti tion Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Sensitivity 1x1 µm Spatial resolution Tri ricks lie lie in in tip tips All ll matters: sen ensit itiv ivity, resolution, in invasivity, , coe oerciv ivity … Non-invasive Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Principle: measure ferromagnetic resonance with MFM Measures the longitudinal (static) moment Magnetic biasing of the sample with the stray field of tip allows some kind of imaging Courtesy: O. Klein, Grenoble Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Example: FMR spectra of a permalloy disk with diameter 1000nm Simulation of FMR modes Measurements O. Klein et al., Phys. Rev. B 78, 144410 (2008) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Principle: spectroscopy of a Nitrogen-Vacancy center in a diamond nanocrystal L. Rondin et al., Nat. Comm. 4, 2279 (2013) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Micromagnetics Sensitivity: image antiferromagnetic domains Assets Square Fe20Ni80 dot High sen Hig sensit itivity Poss ossib ibly quantitative in qu n fi field 5 𝜈𝑛 Qu Quantitativ ive rec econstruction of of mag agnetiz izatio ion pa pattern no not t straig ightforw rward Imag Imaging un under Signature of flux-closure hig high mag agnetic field no fi not t pos possib ible Cr 2 0 3 200nm thin film L. Rondin et al., Nat. Comm. 4, 2279 (2013) P. Appel et al., Nano Lett. 19, 1682 (2019) Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Near-field optics Implementation for magnetic microscopy Courtesy: M. Miron, Grenoble Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic

Out-of-plane magnetization Ultrathin Pt/Co/Pt film Assets Rea easonable spa spatial reso esolu lution Compatible wit Co ith tim ime reso esolu lutio ion Ha Hardly ly qu quantitative AFM P-SNOM Courtesy: M. Miron, Grenoble Olivier FRUCHART – SPM for magnetism ESM2019, Brno, Czech Republic