The phenomena of interlayer exchange coupling (JIEC) between thin ferromagnetic (FM) layers allows materials with precisely tailored properties to be created, and is key to the future development of spintronics. Synthetic ferromagnets (SFMs) have the same FM/Non-magnetic(NM)/FM structure as the widely studied Synthetic Antiferromagnet (SAF) [1], but describe the case where the magnetisation of the two FM layers are aligned in parallel. The structure of a SFM and its resonant dynamics is shown in Fig.1a. It is known that the formation of a double resonance consisting of an Acoustic Mode (AM) and an Optic Mode (OM) requires a difference in layer magnetisation (MDiff) and a FM JIEC [2] [3]. However, to date, a comprehensive description of the resonant properties as a function of JIEC and difference in layer magnetisation has not been reported despite their widespread use in quasi-static devices [4]. Here, we investigate, both experimentally and via numerical simulations, the hitherto uncharted dependence of the observed double resonance on MDiff and JIEC [5]. The samples were fabricated using magnetron sputtering and characterized by X-ray Reflectivity (XRR) to measure layer thickness, vector Vibrating Sample Magnetometry (VSM) to verify AF coupling and a Vector Network Analyser – Ferromagnetic Resonance (VNA-FMR) setup which allows fundamental dynamic properties to be explored. These SFMs exhibited a JIEC consistent with coupling on the 1st FM RKKY coupling peak and have structure Ta(2 nm)/CoFeB(5 nm)/Ru(tRu)/CoFeB(5 nm)/Pt(4 nm) where tRu is the thickness of the ruthenium layer, acting as the non-magnetic spacer layer. Our simulations, performed using MuMax3, show that MDiff and JIEC have orthogonal dependencies on the two resonant modes. We further demonstrate that the conventional understanding of the phases of these modes, described as possessing an in-phase or out-of-phase nature for the AM and OM respectively, does not capture fully the intricacy of the resonant dynamics. Comparison between experimental and simulated data allows MDiff, JIEC and the resonant phases of each mode to be accurately determined. These findings are directly applicable to the creation of tailored SFMs for spintronic devices with applications in STT/SOT-MRAM where control of these parameters is paramount [3] [6].

**References:**

[1] H. J. Waring, N. A. B. Johansson, I. J. Vera-Marun et al., Zero-field Optic Mode beyond 20 GHz in a Synthetic Antiferromagnet, Phys. Rev. Appl., Vol. 13, p. 034035 (2020) [2] B. Heinrich and J. F. Cochran, Ultrathin metallic magnetic films: magnetic anisotropies and exchange interactions, Adv. Phys., Vol. 42, p. 523–639 (1993) [3] T. McKinnon, P. Omelchenko, B. Heinrich et al., FMR study of interlayer exchange coupling in FeCoB|Ta|FeCoB trilayers with in-plane anisotropy, J. Appl. Phys., Vol. 123, p.223903 (2018) [4] T. Devolder, E. Liu, J. Swerts et al., Ferromagnetic resonance study of composite Co/Ni - FeCoB free layers with perpendicular anisotropy, Appl. Phys. Lett., Vol. 109, p.142408 (2016) [5] H. J. Waring, Y. Li, I. J. Vera-Marun et al. Phys. Rev. Lett., Manuscript In Preparation. [6] S. Yakata, H. Kubota, T. Seki et al., Enhancement of thermal stability using ferromagnetically coupled synthetic free layers in MgO-based magnetic tunnel junctions, IEEE Trans. Magn., Vol. 46, p. 2232–2235 (2010)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/b5294be2ca537e2a7cb2e6695213d4ce.jpg)
Fig.1 a) The resonant dynamics of a synthetic ferromagnetic (SFM) system with a ferromagnetic (FM1)/non-magnetic (NM)/FM2 structure and a FM interlayer exchange coupling JIEC. An optic mode is seen in addition to the acoustic mode only in cases where the layer magnetization of FM1 (Ms,1) and FM2 (Ms,2) are different. b) 2D map of the resonant spectra of a SFM when the NM spacer layer, consisting of Ru, thickness tRu = 1.10nm.

 Characterizing Interlayer Coupling in Synthetic Ferromagnetic Thin Films

Antiferromagnets have considerable potential as spintronic materials [1]. Notably, they manifest resonant modes at frequencies higher than can be observed in conventional ferromagnetic materials. Synthetic Antiferromagnets (SAFs), engineered structures of antiferromagnetic (AF) RKKY exchange coupled ferromagnetic(FM)/non-magnetic(NM)/ferromagnetic trilayers, mimic the properties of single phase antiferromagnets whilst possessing greater compatibility with current device technologies such as those used for STT-MRAM production [2,3]. In addition to the conventional acoustic (Kittel) mode, SAFs also possess a higher order resonant (optic) mode [3]. The structure of a SAF is shown in Fig.1a. We report the dynamic properties of SAFs with structure Ta(2 nm)/CoFeB(5 nm)/Ru(tRu)/CoFeB(5 nm)/Pt(4 nm) where tRu is the thickness of the Ru layer, acting as the NM spacer layer. The samples were fabricated using magnetron sputtering and characterized by X-ray Reflectivity (XRR) to measure layer thickness, vector Vibrating Sample Magnetometry (VSM) to verify AF interlayer coupling and a Vector Network Analyser – Ferromagnetic Resonance (VNA-FMR) setup to explore dynamic properties. Fig.1b shows the resonant dynamics of a single CoFeB layer and a CoFeB SAF. The data demonstrate the highest zero field frequencies observed in SAFs to date [4] with resonances of 18 GHz and 21 GHz at the 1st and 2nd instances of AF RKKY coupling respectively. A three part analytical model can reproduce the major features of the measured spectra.References: [1] T. Jungwirth, X. Marti, P. Wadley et al., Nat. Nanotechnol., Vol. 11, p. 231–241 (2016) [2] R. Hao, L. Wang and T. Min, IEEE Trans. Magn., Vol. 55, p. 1-6 (2019) [3] S. Li, C. Wang, X. Chu et al., Adv. Funct. Mater., Vol. 26, p.3738-3744 (2016) [4] H. Waring, N.A.B. Johansson, I. Vera-Marun et al., Phys. Rev. Appl., Vol. 13, p. 034035 (2020)

Zero Field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet

Antiferromagnets have considerable potential as spintronic materials [1]. Notably, they manifest resonant modes at frequencies higher than can be observed in conventional ferromagnetic materials. Synthetic Antiferromagnets (SAFs), engineered structures of antiferromagnetic (AF) RKKY exchange coupled ferromagnetic(FM)/non-magnetic(NM)/ferromagnetic trilayers, mimic the properties of single phase antiferromagnets whilst possessing greater compatibility with current device technologies such as those used for STT-MRAM production [2,3]. In addition to the conventional acoustic (Kittel) mode, SAFs also possess a higher order resonant (optic) mode [3]. The structure of a SAF is shown in Fig.1a. We report the dynamic properties of SAFs with structure Ta(2 nm)/CoFeB(5 nm)/Ru(tRu)/CoFeB(5 nm)/Pt(4 nm) where tRu is the thickness of the Ru layer, acting as the NM spacer layer. The samples were fabricated using magnetron sputtering and characterized by X-ray Reflectivity (XRR) to measure layer thickness, vector Vibrating Sample Magnetometry (VSM) to verify AF interlayer coupling and a Vector Network Analyser – Ferromagnetic Resonance (VNA-FMR) setup to explore dynamic properties. Fig.1b shows the resonant dynamics of a single CoFeB layer and a CoFeB SAF. The data demonstrate the highest zero field frequencies observed in SAFs to date [4] with resonances of 18 GHz and 21 GHz at the 1st and 2nd instances of AF RKKY coupling respectively. A three part analytical model can reproduce the major features of the measured spectra.References: [1] T. Jungwirth, X. Marti, P. Wadley et al., Nat. Nanotechnol., Vol. 11, p. 231–241 (2016) [2] R. Hao, L. Wang and T. Min, IEEE Trans. Magn., Vol. 55, p. 1-6 (2019) [3] S. Li, C. Wang, X. Chu et al., Adv. Funct. Mater., Vol. 26, p.3738-3744 (2016) [4] H. Waring, N.A.B. Johansson, I. Vera-Marun et al., Phys. Rev. Appl., Vol. 13, p. 034035 (2020)


Zero Field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet (B)

*Session Chair: Matthieu Bailleul, Universite de Strasbourg*

These on-demand presentations are available to view at your leisure.

FC: Ghz to THz precessional magnetization dynamics

technical paper

INTERMAG 2021 Welcome Video



	
<figure class="video_container">
 <iframe src="https://screencast-o-matic.com/player/crflqFVnUpZ?v=6&ff=1&title=0&controls=1" width=640 height=360 frameborder="0" allowfullscreen="true"> </iframe>
</figure>

Want to buy a ticket? 

Register for INTERMAG 2021 here

[![](https://assets.underline.io/uploads/markdown_image/1/image/17ce76e7960db633258024eef8d6da7f.png)](https://intermag.org/register)

Got your ticket, but still can’t access the event?

Contact us and our team will look into it.

INTERMAG 2021

M1: Antiferromagnetic Spintronics III

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

We were reluctant to give up the benefits of meeting face-to-face, and know that shifting to a virtual conference is a significant change for this community. Nevertheless, we are first and foremost concerned about the health and safety of all our Conference participants and their loved ones on returning home after travelling.

The MMM 2020 Steering Committee was working exceptionally hard, along with our sponsors, the IEEE Magnetics Society and AIP Publishing, to make this event serve the needs of our participants, who live in time zones all around the globe, in the best possible way. 

You need a ticket to explore this event.

If you have already registered for MMM 2020, and you have already created an account, then you
just need to login (above).

If you have already registered for MMM 2020, but you have not yet created an account, then you
need to click on &quot;create an account&quot; (above) and then login.

Forgot your password? Go to
https://www.underline.io/log-in

If you have not yet registered for MMM 2020 but would like to do so, go to
https://magnetism.org/register

Still need help? Contact our team!


MMM 2020

This session is sponsored by:

![](https://assets.underline.io/uploads/markdown_image/1/image/ea7afa1c2ec66994cb730e3f903a735d.jpg)

Harry Waring

3

SHORT BIO

Presentations

Characterizing Interlayer Coupling in Synthetic Ferromagnetic Thin Films

Zero Field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet

Zero Field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet (B)

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES