Interfacial phenomena in magnetic thin film systems are key to future spintronic applications. For materials close to the Stoner criterion, such as Pt, electronic hybridisation at the interface with a magnetic material results in a proximity induced moment (PIM), with debate ongoing regarding the role of the induced moment with regards to interfacial spin transport [1,2]. Recently, rare-earth:transition metal (RE:TM) ferrimagnetic alloys have shown promise in spintronic applications, due to the net zero magnetisation at the compensation point of the two competing magnetic sub-lattices. This compensation, which occurs as a function of both temperature and alloy composition, enhances domain wall motion [3], thermal switching [4] and leads to vanishing skyrmion Hall angles [5]. However, in multilayered systems, it has not been experimentally shown whether the induced moment in a Pt at the interface with a RE:TM ferrimagnet will align with the net moment, or one of the magnetic sublattices. Here we present the results of a recently published study [6] investigating the magnetic moments in ferrimagnetic / Pt systems, using Co77Gd23 and (Co50Fe50)77Gd23 ferrimagnetic alloys to vary the dominant magnetic sublattice. Temperature dependent SQUID measurements, combined with element specific resonant x-ray measurements at the APS, Argonne Lab on the Pt and Gd L3 edges, allowed for the determination of the alignment of the Gd moments and induced Pt moments on either side of the compensation transition. In both cases, the PIM was found to be parallel to the TM sublattice rather than the RE or the net moment. Our results highlight the prominence of the d−d mediated interactions between the Pt and the constituents of the ferrimagnetic RE:TM alloys over the net macroscopic moment.

![](https://assets.underline.io/uploads/markdown_image/1/image/4ff3a1ca1079ff9c262e75f9fde1108a.jpg)

Fig 1: Element specific hysteresis loops taken at the Pt and Gd L3 edges for CoGd/Pt (Gd dominated) and CoFeGd/Pt (CoFe dominated)

Proximity induced magnetism in Pt layered with rare-earth:transition metal ferrimagnetic alloys

Reservoir computing (RC) is a machine learning paradigm where computational power is obtained from the intrinsic memory and nonlinearity of a dynamic system. Traditionally, the dynamic system is provided by a recurrent neural network, though many recent studies show this network can be substituted with a physical system. Within the field of magnetism, many systems have been proposed as candidates for RC, such as magnetic tunnel junctions (MTJs) [1], skyrmion textures [2], superparamagnetic arrays [3], and even single domain walls [4]. However, aside from MTJs, few of these proposed systems have been experimentally realised. Recently, we showed that single-layer arrays of interconnected permalloy nanorings exhibit emergent domain wall dynamics suitable for computation [5]. Here, we demonstrate RC in materio using a device containing the aforementioned arrays. Data is encoded to the array by modulating the amplitude of a rotating magnetic field. Using two-point resistance measurements, we show that we can extract information on the state of the array through anisotropic magnetoresistance (AMR). These measurements exhibit nonlinearities between applied field and the measured magnetic state of the system, as well as hysteretic memory. Next, we show how we can control the system’s dynamics through scaling of the applied magnetic field, allowing a range of different transfer functions between input and measured magnetic state. These different transfer functions can be exploited to provide improved computational performance on signal, speech, and writing processing tasks. Through optimised scaling of the applied fields, the different computational demands of each task are met on a single device. We believe that the computational versatility, relative simplicity of manufacture, as well as the wide range of available parameter space to further explore makes the ring arrays an exciting platform for neuromorphic computation.

![](https://assets.underline.io/uploads/markdown_image/1/image/2dd48ac941e88dbd5d2d7ca08ddcf6a4.jpg)

Measured AMR response for 4 rotations of 30 Oe applied field, followed by 4 rotations of 20 Oe applied field, showing both nonlinear and hysteretic behaviour.

![](https://assets.underline.io/uploads/markdown_image/1/image/7848690af170509ddac1fd479d8a859f.jpg)

Micrograph of patterned nanoring array and electric contacts taken from RAITH Voyager electron beam lithography system.

Experimental Demonstration of Reservoir Computation using Emergent Domain Wall Dynamics in a Patterned Magnetic Substrate

Spin transport across interfaces is fundamental to many spintronic devices. To fully exploit interfacial phenomena, such as spin-orbit torques and spin-pumping, in ferromagnetic (FM) and heavy metal systems (HM) the properties of both the HM layer and the interface must be considered, particularly in the case of perpendicularly magnetised systems [1]. Previously we showed the evolution of spin transport as a function of FM and HM thicknesses [2] and the role of insulating layers [3]. Debates remains regarding the physical basis of interfacial spin transport and the role of proximity polarisation of the HM layer [4]. A notional ‘spin memory loss’ term is often used to represent an interfacial contribution, while for Pt in particular, a magnetic polarisation arises in proximity (PIM) to a ferromagnetic material, opens a question about the role that PIM has upon interfacial spin phenomena, with contradictory reports that it has either a profound effect [5] or no effect [6] on spin transport. Here we present the results of a detailed systematic spin transport and PIM study in the same FM/HM samples. Structures with either a constant Pt thickness and a spacer layer thickness wedge, or a constant spacer layer and a Pt wedge were deposited. A combination of dynamic and static magnetic measurements, along with element specific resonant x-ray measurements at the APS, Argonne Lab, were used to address both the interfacial scattering contribution and the role of PIM in Pt on spin transport and to determine their relative contributions. Figs. 1 and 2 show damping and PIM data, with a persisting Pt moment with a 3nm Au layer, and a clear trend observed between the PIM and dynamic behaviour. These results highlight the role of the d-d orbital hybridisation and the induced moment for efficient interfacial transport, which is key for many spintronic applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/ca60624dc0cead773db990e20080f85b.jpg)

Fig 1: Measured XMCD as a function of Au spacer thickness at both the Pt (blue) and Au (orange) L3 edges for NiFe (7 nm)/ Au / Pt (4 nm)

![](https://assets.underline.io/uploads/markdown_image/1/image/f3928c773ef3592e934476655f51d0ce.jpg)

Fig 2: Damping and Pt XMCD for CoFe/Au/Pt and NiFe/Au/Pt. Dotted lines indicate bulk damping contributions.

The role of proximity induced magnetism on spin transport in multilayered systems

**Session chairs:** Ricardo Ferreira, INL - International Iberian Nanotechnology Laboratory and Akinobu Yamaguchi, University of Hyogo


EOD - Thin Films Ι

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

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Please register for the Joint MMM-Intermag conference to join the event.

2022 Joint MMM-INTERMAG

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

**Session chair:** Stephane Mangin, Université de Lorraine


GOK - MRAM, Magnetic Logic and Related Devices I

**Session chair:** Kyongmo An, Korea Research Institute of Standards and Science


Charles Swindells

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Proximity induced magnetism in Pt layered with rare-earth:transition metal ferrimagnetic alloys

Experimental Demonstration of Reservoir Computation using Emergent Domain Wall Dynamics in a Patterned Magnetic Substrate

The role of proximity induced magnetism on spin transport in multilayered systems

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