Iron-gallium (FeGa) is one of the most promising magnetic materials for use in composite multiferroics due to its high piezomagnetic coefficient (3 ppm/Oe) and high stiffness (70 GPa). It has been integrated into several multiferroic systems, but generally in MHz range or below.¹ In order to make it suitable for high frequency (GHz) applications, metalloid dopants have been used to soften magnetic materials and enhance their frequency dependent properties, but at the cost of the saturation magnetization as well as magnetoelastic properties.² A viable approach to circumvent this trade-off problem is to integrate a magnetic material with complementary properties into magnetic heterostructures. In this work, multilayer laminates were fabricated with FeGa and NiFe, a material with excellent properties in high frequency regimes.

FeGa (hard) and NiFe (soft) were sputtered via alloy targets with compositions Fe₈₅Ga₁₅ and Ni₈₁Fe₁₉ (at%) into multilayers with layer thicknesses ranging from 3-50 nm, with FeGa being used as the first and last layer in the stack. XPS confirmed the composition and showed there was no intermixing of the layers. Static magnetic properties were evaluated via SQUID magnetometry, and it was found that the incorporation of NiFe layers reduced the coercivity by up to 85%, from 30 Oe to 4 Oe. FMR studies showed a reduction of the linewidth of up to 50%, from 70 Oe to 38 Oe. It is believed that this effect is largely due to the decrease of magnetic anisotropy dispersion in the multilayers.³ The multilayer films maintained a high magnetostriction of up to 190 ppm, on the same order of magnitude as giant magnetostrictive materials such as thin film Terfenol-D.⁴ FeGa/NiFe heterostructures have been shown to be an excellent candidate for strain-coupled microwave multiferroics.

References:

1.M Hamashima, C Saito, M Nakamura and H Muro, ECJ (5), 1-7 (2012).

2.J Lou, RE Insignares, Z Cai, KS Ziemer, M Liu and NX Sun, APL (18) (2007).

3.R. Nakatani, T Kobayashi, S Ootomo and N Kumasaka, JJAP 27 (6) (1988).

4. KP Mohanchandra, SV Prikhodko, KP Wetzlar, WY Sun, P Nordeen and G. P. Carman. AIP Advances 5 097119 (2015).