Recent Developments in Fe-Based Electrodeposited Thin Films
Authors: Coton Noelia , Begue Adrian , Jaafar Miriam , Maicas Marco , Andres Juan Pedro , Ranchal Rocio 
Published: August 2024

Electrodeposition is a commonly employed technique for synthesizing magnetic thin films, serving both fundamental research and practical applications. Of particular interest are Fe-based alloys like NixFe1-x and Fe1-xGax, as fundamental properties of ferromagnets as saturation magnetization (Msat), Curie temperature (TC), magnetic anisotropy (K) and magnetostriction constant (λ) strongly depend on the composition [1-2]. This work presents our latest findings on Fe-based thin films and multilayers, exploring diverse phenomena ranging from controlling magnetization switching in magnetoelastic structures to fine-tuning the out-of-plane (OOP) component of magnetization [3-4].
Materials exhibiting moderate perpendicular magnetic anisotropy can develop stripe domains above a critical thickness (tcr). In addition to the interest in the basic understanding of this magnetic texture, nowadays, there is an increasing attention in this type of domains since they can be used for example for spin waves generation. The Ni80Fe20 alloy known as permalloy has been widely investigated because of its low coercivity and null magnetostriction. Sputtered Ni80Fe20 layers has been reported to have tcr around 300 nm [5], and its formation is generally believed to be due to columnar growth. However, for applications like magnetoimpedance, these stripes can be undesirable, hindering the growth of sufficiently thick layers to fabricate reliable sensors. Therefore, it is of interest the control of stripe domains in NixFe1-x films and whether the electrodeposition technique can also be used to tailor the appearance of this magnetic texture. Initially, we have examined the formation of stripe domains in the Ni90Fe10 alloy that is also of great interest because of its low coercivity and negative magnetrostriction (λ ~ -20 ppm). Subsequently, we have analyzed the magnetic behavior of electrodeposited NixFe1-x films in which the Fe content has been increased up to 30 at. %. Experimental results show that for Ni90Fe10 films magnetic stirring during growth suppresses the presence of stripes even for a thickness exceeding 1 µm. On the other hand, when growing with unstirred electrolyte, tcr can be reduced if a perpendicular magnetic field of 100 Oe is applied during samples growth. Eventually, it has been observed that tcr depends on the Fe content in the NixFe1-x and no stripes are observed for a content above 13 at.% when no perpendicular magnetic field is applied during growth.
We have also investigated a bilayer structure comprised of two magnetic layers with opposite signs for the magnetostriction constant, Ni90Fe10 (λ ~ -20 ppm) and Fe70Ga30 (λ~ 70 ppm) to analyze the effect of magnetoelasticity on the magnetization reversal process. The exchange correlation length is a key parameter that determines the transition region between two opposite directions of the magnetization that depends on characteristics such as the magnetic anisotropy and the exchange stiffness constant. It is also used to quantify the domain wall thickness (δ) that can be considered as the distance over which the magnetic moments are correlated by exchange interactions, and that plays a fundamental role on magnetic systems relying on interfacial interactions as spring magnets or exchange-biased systems. Since the thickness of the layers cannot be higher than δ to avoid the magnetic switching of uncoupled regions, this implies that the thickness of layers is intrinsically limited in systems with interfacial coupling. We have studied Ni90Fe10/Fe70Ga30 bilayers with thicknesses exceeding δ to analyze the magnetic switching in these new magnetoelastic bilayer structures. 500 nm-thick Ni90Fe10 and Fe70Ga30 single layers have coercive fields of 22 Oe and 42 Oe, respectively, which guarantees that independent magnetic switchings from each layer can be experimentally observed.This has been confirmed by micromagnetic simulations performed by OOMF in which magnetoelasticity has not been included. However, when measuring the hysteresis loops of different NiFe/FeGa samples with thicknesses exceeding δ it is observed an in-unison magnetization reversal in all cases. Since magnetoelasticity is not an interfacial effect, it enables to control the magnetization reversal process of the whole bilayer regardless of the thickness being possible to promote this simultaneous reversal process regardless of the layer thickness (Fig.1).
In conclusion, these results highlight the capability of electrodeposition to achieve new magnetic systems with enhanced functionalities.
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[2] Q. Xing, Y. Du, R. J. McQueeney, T. A. Lograsso. Acta Mater. 56 (2008) 4536−4546.
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[4] N. Coton, J.P. Andres, E. Molina, M. Jaafar, R. Ranchal. J. Magn. Magn. Mater. 565 (2023) 170246.
[5] M. Romera, R. Ranchal, D. Ciudad, M. Maicas, C. Aroca, J. Appl. Phys. 110 (2011) 083910

Figure 1