Journal of Materials Research 2022 www.mrs.org/jmr Vol.:(0123456789) DOI:10.1557/s43578-022-00667-2 Modifcations in ferromagnetic properties of MnAl bilayer thin flms induced by swift heavy ion irradiation H. Khanduri 1,a) , Mukesh C. Dimri 2,a) , S. A. Khan 3 , Prashant Kumar 1,4 , J. Link 5 , R. Stern 5 , Nanhe Kumar Gupta 6 , R. P. Pant 1,4 1 Indian Reference Materials Division, CSIR-National Physical Laboratory, New Delhi 110012, India 2 Jaypee University of Engineering and Technology, Guna, MP 473226, India 3 Inter-University Accelerator Centre, New Delhi 110067, India 4 Academy of Scientifc and Innovative Research (AcSIR), Ghaziabad 201002, India 5 National Institute of Chemical Physics and Biophysics, 12618 Tallinn, Estonia 6 Tin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India a) Address all correspondence to these authors. e-mails: himani.khanduri@gmail.com; mukeshdimri@yahoo.com Received: 12 May 2022; accepted: 15 July 2022 In this paper, we report the efects of swift heavy ion (SHI) irradiation on structural, microstructural, and magnetic properties of Mn/Al bilayer thin flms deposited by the evaporation technique. The as-deposited thin flms were irradiated by a 100 MeV Ag ion beam with diferent fuences (1 × 10 13 –1 × 10 14 ions/cm 2 ). The enhanced ferromagnetic properties with perpendicular magnetic anisotropy have been achieved in the irradiated flms with the increase in irradiation fuence, which were supported by the GIXRD, VSM, and MOKE results. The AFM study suggests that the average grain size was obtained in the range of 32–67 nm for all the flms. The present study demonstrates that SHI irradiation improves the ferromagnetic properties of Mn/Al bilayer thin flm, which makes it a promising material for rare-earth-free permanent magnets and spintronic applications. Introduction The rare-earth-free permanent magnets have gained much importance in recent years due to the limited sources of rare earth elements. As the requirement of permanent magnets in the technology is enhancing day by day, we need to use rare-earth- free permanent magnets, which have good magnetic proper- ties, lower cost, and abundance in nature. MnAl alloy has been reported as a potential material for rare-earth-free permanent magnets. Te strong perpendicular magnetic anisotropy, high coercivity, good corrosion resistivity, and high energy product make it a promising material for various applications such as data storage, perpendicular magnetic anisotropic material, and magnetic recordings [1–3]. Te thin flm form of MnAl alloy has gained more interest than the bulk form because of the stabiliza- tion of the ferromagnetic τ-phase at room temperature in the MnAl thin flms, whereas the ferromagnetic τ-phase decom- poses into β- and γ-phases in the bulk form [4, 5]. β- is a phase of manganese while γ- is a non-magnetic phase of MnAl alloy [5]. Among the various crystalline phases, τ-phase is the only ferromagnetic phase present in the binary MnAl alloy system, for which the atomic compositions should be in the range of 50–60% [5, 6]. Te tetragonal crystal structure of τ-phase MnAl alloy is shown in Fig. 1(a). Te ferromagnetic τ-phase can be achieved in MnAl thin flms by cooling of the ɛ-phase of MnAl followed by controlled annealing in the higher temperature range of 350–650 °C [7, 8]. Metal alloys formation by ion beam mixing has been reported in various studies [9–12]. Also, the modifcations in the structural, magnetic, optical, and electrical properties of the metal and alloy thin flms by ion beam irradiation have been studied extensively [13–18]. Te mixing mechanism of lay- ers present in a bilayer or multilayer thin flm depends on the energy of the irradiating ions. When the energy of a heavy ion is from tens to hundreds of keV, the preferable loss of kinetic energy has been found to happen by elastic collision (nuclear stopping power, S n ) of the ion with the atoms present in the material [19]. As the ion passes through the layered system, the formation of a recoil cascade takes place which results in the intermixing of atoms present at diferent layers near the interface [20, 21]. However, for the ions having the energy of the order © The Author(s), under exclusive licence to The Materials Research Society 2022 Article