Magnetoelectric Functionality of Ni–Mn–In-Encapsulated AlN/Ni–Mn–In/Ni-Graded Heterostructure for Flexible Magnetic Field Sensor

Nowadays, flexible magnetoelectric (ME) heterostructures comprising lead-free piezoelectrics are of considerable interest for commercializing wearable electronic devices such as energy harvesters, nonvolatile memory, implantable medical diagnostics, and sensors. Here, we fabricate a highly flexible, cost-effective, nanostructured magnetic field sensor comprising an AlN/Ni–Mn–In ME heterostructure over Ni foils. The functionality of the AlN/Ni–Mn–In/Ni heterostructure has been investigated by measuring the magnetodielectric MD (%) and magnetoelectric coupling (α ME ) coefficient with Ni–Mn–In thickness, anisotropy, and flexibility. The thickness ratio of piezoelectric AlN (∼400 nm) and magnetostrictive Ni–Mn–In (∼385 nm) layers has been optimized to achieve the high performance of the magnetic sensor. The encapsulation of the Ni–Mn–In layer drastically enhances the performance of the fabricated heterostructure. The highest MD ∼ 2.95% and α ME ∼ 3.2 V/cm·Oe have been recorded with an equal thickness ratio of AlN and Ni–Mn–In layers. It could be ascribed to the large magnetostrictive strain transferred to the AlN piezoelectric layer, which enhances the induced ME voltage. Moreover, the nonzero value of α ME at zero bias magnetic field has been observed and related to the piezomagnetic coefficient ( q ) grading in the Ni–Mn–In(+ q )/Ni(− q ) ferromagnetic system, which enhances the strength of magnetoelectric coupling. The fabricated device has easily detected the ultralow magnetic field of up to or less than ∼1 μT. In addition, the anisotropic functionality of the device has been explained by measuring the magnetodielectric and magnetoelectric characteristics in parallel and perpendicular dc bias fields. The MD and ME characteristics remain stable up to 2500 bending cycles. Hence, the present lead-free ME heterostructure integrated over a flexible Ni foil can enhance the multifunctionality of futuristic flexible magnetic field sensors for room-temperature applications.