The Effect of Thickness‐Tunable ZrO₂ Shell on Enhancing the Tunneling Magnetoresistance of Fe₃O₄ Supraparticles

Abstract

at room temperature. This degradation is caused admittedly by the reduced spin polarization due to the multiple effects of oxidation, defects, bonding, and surface reconstruction at the surfaces or interfaces of the polycrystal grain boundaries. Comparing to bulk materials, the nanoparticles can produce enhanced extrinsic MR owing to the effect of spin-dependent interface scattering or tunneling through the boundaries. [18] Additionally, the MR can still be increased by core-shell encapsulated structures. For example, an insulating shell coats on the magnetite core. In such a dielectric system, nanometric ferromagnetic particles show giant TMR by spin-dependent tunneling of conducting electrons at the magneticinsulator interfaces. Electrons with spin parallel to the particle magnetization have a bigger probability of tunneling than electrons with antiparallel spin, resulting in an overall lower resistance. Similar MR enhancement has been realized in Fe 3 O 4 @SiO 2 , [19] Fe 3 O 4 @ oleic acid, [20] Fe@Cr, [21] and Fe 3 O 4 @ZnS [22] system. Insulator zirconium dioxide (ZrO 2 ) is a nonmetallic inorganic material and has excellent resistance to acids and alkalis. It was widely applied in catalyst carrier and thermal barrier fields due to the stability and insulativity. Previous studies have shown that ZrO 2 doping in the perovskite systems can effectively enhance the magnetoresistance. [23][24][25] To the best of our knowledge, it is still unexploited of ZrO 2 doping in the half-metal Fe 3 O 4 nanoparticles by means of the core-shell structural system.In this paper, Fe 3 O 4 @ZrO 2 core-shell nanocomposites are prepared with controllable shell thickness and core-size. The pomegranate-like core is obtained and composed of several monocrystals and single-domain Fe 3 O 4 nanocrystals with size <10 nm. The magnetic structure and magnetotransport property of the core-shell nanocomposites are explored. Our results show that the MR is increased to ≈7.5% at 2 kOe in this core-shell system compared to that of pure Fe 3 O 4 nanoparticles ≈4.7%. Moreover, as Zr content increases, the MR first increases and then decreases. This is because the addition of insulated barrier promotes the tunneling effect, which enhances the MR, but with further increase of ZrO 2 thickness, the barrier becomes larger and the electron tunneling becomes difficult, leading to the reduced MR. In addition, the results of Fe 3 O 4 @ZrO 2 with different core sizes show that the MR rises monotonically with a decrease of the size of core. Moreover, for eliminate the possible effect of ZrO 2 permeating into the interior of the pomegranate-like core, fault-cutting is prepared andThe core-shell Fe 3 O 4 @ZrO 2 nanoparticles with controllable shell thickness and core dimensions are synthesized using solvothermal approaches. The introduction of the insulator ZrO 2 shell allows realizing the enhancement of tunneling magnetoresistance (TMR) effect of the functional nanomaterials. The influences of temperature, magnetic field, and shell thickness on the TMR are ...

Current Progress of Magnetoresistance Sensors

“…Breakthroughs are expected to improve the performance and reduce the manufacturing cost of devices with built-in MR units, which overcome existing challenges and benefit the future application of MR sensors. The low magnitude of AMR outputs (∆R/R 0 < 2.5%) Difficult to reduce the size and hard for miniaturization [8,9] Multilayer systems based on GMR and TMR GMR/TMR multilayer systems exhibit high sensitivity for low magnetic fields GMR/TMR multilayer systems can be integrated with the electronic circuit easily Multilayer structures require complicated fabrication processes and specific equipment due to the strict limitations of layer thickness (increasing cost on equipment and extending the fabrication process lead to expensive products) GMR/TMR multilayer systems exhibit limited resistance variation range (working range, especially for TMR) and relatively low MR at room temperature (mostly for GMR) [52][53][54][55][56][57][58][59][60][61][65][66][67] Granular MR systems Granular MR systems bring simplified fabrication procedures and reduced investments in instruments Relatively large MR at room temperature can be achieved by some specifical designed granular MR systems Magnetic field ≥ 50 kOe is the prerequisite to achieve large MR at ambient temperature (relatively small resistance change for low magnetic fields at room temperature) Some granular MR systems require extremely low temperatures for large MR Although granular MR systems can reduce the complexity of the fabrication process, the dependence on specific fabrication techniques (such as magnetron sputtering) remains [23][24][25][68][69][70][71][72][73][74] Layered graphene MR systems Layered graphene MR systems exhibit large MR value and potential to be applied on fabricating next-generation spintronics based on layered graphene Most layered graphene MR systems require extremely low temperatures to achieve large MR Special designed substrates/circuits are required Precise control of layer number and positions is challenging Special fabrication techniques are required for preparing layered graphene, which further increases the production costs and the complexity [30]…”

“…Chemically synthesized Fe 3 O 4 nanoparticles are adopted in constructing granular MR systems because of their accessibility, stability, and large magnetization. The Fe 3 O 4 granular MR systems achieved −1.6% and −1.2% of resistance change at 5 kOe for thin film and pressed powder [68] [25,[69][70][71]. These granular systems achieved a large linear working range (~2 T) and relatively large negative MR responses (−4%~−8%).…”

“…The Fe3O4 granular MR systems achieved −1.6% and −1.2% of resistance change at 5 kOe for thin film and pressed powder [68]. Various granular MR systems were developed based on core-shell structures of Fe3O4 including Fe3O4@SiO2, Fe3O4@ZnS, Fe3O4@ZrO2 and MgO@Fe3O4 [25,[69][70][71]. These granular systems achieved a large linear working range (~2 T) and relatively large negative MR responses (−4%~−8%).…”