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Lin et al. Soft Sci 2023;3:14 https://dx.doi.org/10.20517/ss.2023.05 Page 3 of 25

Table 1. Representative magnetic nanomaterials
Working Representative
Type Manufacturing approaches References
principle materials
Nanomembranes/nanostructures GMR effect Co/Cu, NiFe/Cu Molecular beam deposition,
sputtering, electrodeposition, [72,73,81]
printing
AMR effect NiFe, NiCo Sputtering, thermal evaporation [87,91,95]
TMR effect CoFeB/MgO/CoFeB, Co/ Sputtering, transfer printing [99,100,104]
Al O /Alq /NiFe
2
3
3
Magnetic composites Hard-magnetic NdFeB particles, CrO 2 3D printing, molding, laser heating [146,160,164]
particles
Soft-magnetic Iron particles, Soft lithography, magnetic field- [126,128,170]
NiFe particles assisted molding
Superparamagnetic Iron oxide nanoparticles Thermal curing, laser/mechanical [149,150,165]
cutting
AMR: Anisotropic magnetoresistance; GMR: giant magnetoresistance; TMR: tunneling magnetoresistance.

focus on robotic systems. In the end, a concluding section summarizes the main advantages and
applications of soft electronics and robotics based on magnetic nanomaterials, and presents some thoughts
for the further development of this field.

SOFT ELECTRONICS BASED ON MAGNETIC NANOMEMBRANES/NANOSTRUCTURES
Electronic devices that can detect the intensity and direction of magnetic fields are important for
applications spanning from motion tracking in consumer electronics to in vitro assays in biomedicine [61,62] .
Soft electronics with such capabilities provide additional possibilities, such as on-skin, tattoo-like
navigation, and in vivo multimodal sensing. Superconducting quantum interference device (SQUID) and
optical-pumping magnetometer (OPM) are important techniques for magnetic field sensing, but they
require low temperatures, bulky wires, or optical fibers that are not compatible with soft electronics [63-66] . In
contrast, the MR effect relies on materials constructed in the format of nanomembranes or other
nanostructures to detect magnetic fields. The ultrathin feature (thickness in the nanoscale) of these
materials allows for their construction in a miniaturized and flexible format. In Sections “Soft electronics
based on GMR effect”, “Soft electronics based on AMR effect”, and “Soft electronics based on TMR effect”,
we discuss soft electronics based on giant magnetoresistance (GMR), anisotropic magnetoresistance (AMR),
and tunneling magnetoresistance (TMR) effects, respectively.

Soft electronics based on GMR effect
The GMR effect primarily relies on multilayer nanostructures made up of alternating ultrathin
ferromagnetic (FM) and non-magnetic (NM) conductive layers, each with a thickness of a few
nanometers [67-69] . Figure 2A shows the schematic illustration of a simplified GMR sensor, where one NM
layer is sandwiched between two FM layers. In the absence of a magnetic field, the FM layers are in a
random magnetization direction, and can be modeled as antiparallel configurations using a tri-layer
structure [middle frame of Figure 2A]. In this case, both spin-up and spin-down electrons encounter strong
scattering, thereby causing high resistance. When an external magnetic field is applied, the FM layers can be
induced into parallel alignment, allowing spin-up electrons to pass through with little scattering, and
strongly scattering spin-down electrons. The clear paths for spin-up electrons result in low electrical
resistance of the GMR structure [right frame of Figure 2A]. Recent advancements in material science and
electrical engineering yield a diverse set of GMR structures, including magnetic multilayer structures, spin
valve trilayer structures, and magnetic granular structures [70,71] , with materials ranging from multilayers of
Co/Cu to NiFe/Cu and others [72,73] . Among the various GMR structures, the spin valve trilayer structures