Achieving Boolean logic via shape anisotropy is not a foreign concept and the usage of fringe field-based interactions between single-domain nanomagnets has been explored [1-2]. However, bi-material ASI systems to fulfil two-input Boolean logic has not been reported. We are motivated to explore field-orientation-dependent logic-based reversal on bi-material structures. Co and Py nano-trapezoids orientated at 90Â° were fabricated via self-aligned stepwise nanosphere lithography [3] forming L-shape structures. Field-orientation dependent magnetization reversal studies were conducted via MFM by applying magnetic field at different angles and values. Fig.1(a) shows the AFM image while Fig.1(b-e) show the remnant magnetic domain images after applying a saturation field of 3 kOe at various field angles. Different configurations of Co (red) and Py (blue) can be defined as logic 0 or 1, as shown in Fig.2(a). The configurations can be divided into four stable and repeatable states â€˜00â€™, â€˜10â€™, â€˜11â€™, '01â€™ which agree well with MFM in Fig.1(b-c) respectively. All the conceivable states vs various orientations are shown in Fig.2(b). The one-in-one-out configuration, which can be attained when the structures are magnetized along the geometrical easy axis for each component, was found to be the most stable [4]. By setting this as logic 0 and others as logic 1, each L-shape can be considered as a two-input XOR gate. Under various external field values and orientation, the magnetic switching behavior of bi-material L-shape structures will be explored by MFM and compared to OOMMF [5] simulation results. Our preliminary simulations show that the bi-material system exhibits three stable states which can be set as logic 0 and 1 whereas the pure material system only produced two stable states which can only be set as logic 0. We will explore how the bi-material system can be exploited to fulfil other logic functions.

Study of field orientation dependent logic for bi

2D bi-material artificial spin ice systems have been well studied [1-4] but restricting spins to 2D limits functionality. Extending into 3D provides an extra degree of
freedom, but the underlying physics need deeper understanding. We show how spin stability can be controlled via introduction of mixed materials and overlap layer (OL) in 3D
nanostructures (NS), with potential applications in computation and memory [5].
Self-aligned hexagonally arranged Py and Co NS were fabricated via stepwise nanosphere lithography [6] via a two-step deposition at different orientation. A mixture of Co NS, Py NS and
3D overlapped Co/Py NS (OLNS) comprising of a Co parallelogram on top of a Co/Py base layer is formed (Fig 1a&b).
Magnetization reversal studies were done via MFM. Fig 1c-f show remanant domain configurations at different field values. After +3 kOe saturation (Fig 1c), most Py NS (circled)
reversed at -300 Oe (Fig 1d). At -700 Oe (Fig 1e), a Co NS reversed (circled) while OLNS exhibited stable transition states (arrows). OOMMF [7] simulations showed a Néel wall (circled)
in Fig 2a but none in Fig 2b for NS without OL. Shape anisotropy causes spins in the OL to lie along the geometrical easy axis. Vertical spins of the Néel wall also connect spins in the base
layer and OL via strong exchange coupling, causing in-plane spins to remain unperturbed over large fields.
The in-plane spins were seen in Fig 2a to also pin nearby spins in the base layer outside the OL in the same direction (light blue), resulting in the stable transition state in Fig 1e. In contrast,
reversal begins at the constituent NS' corners without any OL, as seen in Fig 2b (circled).
The tunability of spin stability via OL's shape and area, material and size will be further discussed via experiments and simulations. These interesting static observations in 3D show
promise for new dynamic spin wave propagation behavior in 3D. This study aims to extend well-established static and dynamic magnetic behavior of 2D structures into 3D. 


**References:** 

[1] A. Rodríguez, L. Heyderman, F. Nolting, Appl. Phys. Lett., vol. 89, p. 142508 (2006) 
[2] S. Choudhury, S. Saha, R. Mandal, ACS Appl. Mater. Interfaces, vol. 8, p. 18339 – 18346 (2016) 
[3] A. O. Adeyeye, S. Jain, and Y. Ren, IEEE Trans. Magn., vol. 47, p. 1639 – 1643 (2011) 
[4] S. Choudhury, S. Pan, S. Barman, J. Magn. Magn. Mater., vol. 490, p. 165484 (2019) 
[5] S. Sahoo, A. May, A. van Den Berg, Nano Letters, vol. 21, no. 11, p. 4629-4635 (2021) 
[6] B. Myint, D. Yap and V. Ng, Nano Express, vol. 1, p. 020029 (2020) 
[7] M. Donahue and D. Porter, OOMMF User’s Guide, Version 1.0 Interagency Report NISTIR 6376 (1999) 

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Controlling Spin Stability in Three Dimensional Bi

LOA: Thin Films and Patterned Structures

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