Magnetic tunnel junctions (MTJs) have been widely utilized in sensitive sensors, magnetic memory, and logic gates due to their tunneling magnetoresistance. Moreover, these MTJ devices have promising potential for renewable energy generation and storage. Compared with Si-based devices, MTJs are more tolerant to electromagnetic radiation. In this review, we summarize the functionalities of MgO-based MTJ devices under different electromagnetic irradiation environments, with a focus on gamma-ray radiation. We explore the effects of these radiation exposures on the MgO tunnel barriers, magnetic layers, and interfaces to understand the origin of their tolerance. This review enhances our knowledge of the radiation tolerance of MgO-based MTJs, improves the design of these MgO-based MTJ devices with better tolerances, and provides information to minimize the risks of irradiation under various irradiation environments. This review starts with an introduction to MTJs and irradiation backgrounds, followed by the fundamental properties of MTJ materials, such as the MgO barrier and magnetic layers. Then, we review and discuss the MTJ materials and devices’ radiation tolerances under different irradiation environments, including high-energy cosmic radiation, gamma-ray radiation, and lower-energy electromagnetic radiation (X-ray, UV–vis, infrared, microwave, and radiofrequency electromagnetic radiation). In conclusion, we summarize the radiation effects based on the published literature, which might benefit material design and protection.

Anisotropic diamagnetism of pristine graphite and graphene is well known. Here, evidence of significant induced ferromagnetism in multilayer graphene (MLG) decorated with ferrimagnetic Fe₃O₄ particles is reported. This MLG-Fe₃O₄ nano-composite was prepared by a one-step ultrasonic treatment at 75 °C in the surfactant sodium dodecyl-benzene-sulfonate. To verify the phase structure and morphology of the composite, X-ray diffraction, scanning and transmission electron microscopy, scanning tunneling electron microscopy, and Raman spectroscopy were employed. Room temperature data of magnetization versus magnetic field showed that the saturation magnetization M_S = 58.6 emu/gm for pristine Fe₃O₄ increased to M_S = 158.4 emu/gm for a 1:1 composite of Fe₃O₄ to MLG. These results lead to induced M_S = 253 emu/gm in MLG resulting from its proximity to Fe₃O₄. Similar experiments on Fe₃O₄ to single walled carbon nanotubes (SWNT) composite did not show any induced magnetism in SWNT.

Composites of anisotropic diamagnetic multilayer Graphene (MLG) and ferrimagnetic CoFe₂O₄ (CFO) nanoparticles (NPs) were synthesized through a one-step sonication process in the presence of a surfactant. The samples were characterized at ambient using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, magnetic force microscopy (MFM) and magnetometry (vibrating sample magnetometer). An induced ferromagnetism was observed in MLG with saturation magnetization M_S = 18 emu/g(MLG). This induced ferromagnetism is attributed to ferrimagnetic CFO uniformly distributed on the surface of diamagnetic MLG. SEM images confirm uniform dense distribution of CFO nanoparticles on MLG. MFM images confirm the formation of larger magnetic domains in the composite sample of MLG/CFO. The measured coercivity H_C = 3.6 Oe of MLG/CFO composite is much smaller than H_C = 32.4 Oe of pristine CFO NPs; this difference in H_C is attributed to the effect of change in surface anisotropy.

Smart materials usually are either mounted on surfaces or embedded inside; in this work, we study magnetic properties of smart materials that are integrated into the structure. Magnetostrictive particles of Tb_xDy_1−xFe₂ (x ∼ 0.3), commonly known as Terfenol-D, incorporated into carbon fiber reinforced polymers showed a 3000% enhancement in the coercive field compared to the reference pristine bulk Terfenol-D. Torque magnetometer measurements revealed a magnetic anisotropy with twofold symmetry. The lowest applied field at which a reversible torque without hysteresis occurred was ∼5.0 kOe, which yields 5 Oe anisotropic field for a carbon fiber reinforced polymer magnet. This value of the anisotropic field is confirmed using the Miyajima method. Angle dependent coercive field and saturation/remanent magnetization also confirmed the twofold symmetry of magnetization in this system. The high magnetostrictive coefficient, together with the enhanced coercive field, makes Terfenol-D integrated into carbon fiber reinforced polymers serve as an excellent candidate for in situ sensing of damage in various polymer composites under several mechanical loading conditions.

Nanocomposites of cobalt ferrite (CFO) magnetic nanoparticle intercalated carbon nanotubes (CNTs) are evaluated as a nanomagnetic ultrasensitive sensor for an environmental toxin, hexavalent chromium (Cr-VI). Specifically, the structural and magnetic changes that accompany the infiltration of the CFO/CNT composite by Cr-VI are presented. The extended x-ray absorption fine structure shows that the atomic spacing within the CFO structure changes in the presence of Cr, suggesting that the Cr is incorporated into the nanoparticles. Vibrating sample magnetometry (VSM) reveals that the CFO/CNT composite infiltrated with Cr-VI has a 71% enhancement in saturation magnetization compared with the uninfiltrated CFO/CNTs, while small-angle neutron scattering (SANS) suggests that this magnetic enhancement is not associated with the nanoparticle length-scales, but may arise from longer-ranged clusters. Both VSM and SANS clearly demonstrate that the Cr-doped CFO/CNTs are hysteretic with a net magnetization at remanence that is about 1/3 of saturation, while this hysteresis is absent in the undoped CFO/CNTs. These magnetic differences in either remanence or saturation are promising for the magnetic detection of Cr-VI using CFO/CNT sensors.