Magnetoresistance Phenomena in Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) comprise two magnetic electrodes separated by an ultrathin insulating barrier, typically magnesium oxide. When electrons tunnel quantum mechanically through the barrier, the junction resistance depends sensitively on the relative orientation of the electrode magnetisations. This tunnelling magnetoresistance (TMR) effect arises from spin-dependent density of states at the interfaces and coherent tunnelling of electrons with particular symmetry channels. Advances in epitaxial growth and interface engineering have yielded room-temperature TMR ratios exceeding several hundred per cent, underpinning the adoption of MTJs in non-volatile memory and magnetic sensors. More recently, antiferromagnetic electrodes and higher-order multipole textures have extended the magnetoresistance phenomena beyond conventional ferromagnetic devices, promising ultrafast switching speeds and enhanced stability against external fields. Throughout these developments, control of crystallographic orientation, barrier thickness and interfacial atomic structure has proven critical. Grain boundaries, barrier roughness and disorder at the interface can limit the maximum achievable TMR by shunting currents or disrupting coherent tunnelling. Emerging applications in neuromorphic computing and spin logic exploit intrinsic device stochasticity, non-volatility and oscillatory behaviour of MTJs. Together, these phenomena highlight the global significance of MTJs for energy-efficient information storage, advanced computing paradigms and next-generation spintronic circuits.

Research from Nature Portfolio

Recent studies have demonstrated tunnelling magnetoresistance in fully antiferromagnetic junctions, in which two antiferromagnetic electrodes with chiral cluster octupole order are separated by a thin oxide barrier. In such devices, switching the relative octupole orientation yields a reproducible TMR ratio of around 2 per cent at room temperature, a value that exceeds expectations based on single-particle spin polarisation. The enhanced response is attributed to time-reversal symmetry breaking associated with cluster magnetic octupoles and anisotropic spin-polarised currents in the antiferromagnet. This work establishes a new paradigm for ultrafast, robust spintronic devices without net ferromagnetic moments. Another line of enquiry has combined atomic-resolution transmission electron microscopy and first-principles calculations to reveal how tilt grain boundaries in textured MgO barriers locally reduce the band gap by several electronvolts. A model of current shunting through these defects shows that even a small fraction of boundary-mediated tunnelling can impose fundamental limits on maximum TMR ratios. These insights guide strategies for barrier optimisation and defect minimisation in high-performance MTJs.

Magnetoresistance Phenomena in Magnetic Tunnel Junctions publication trend

The graph below shows the total number of articles in magnetoresistance phenomena in magnetic tunnel junctions across all publications each year (not limited to Nature Index journals).

Technical terms

Magnetic tunnel junction (MTJ): A device with two magnetic electrodes separated by a nanometre-thin insulating barrier, exploiting spin-dependent tunnelling.

Tunnelling magnetoresistance (TMR): The variation in electrical resistance of an MTJ when the magnetic alignment of its electrodes switches between parallel and antiparallel.

Spin polarisation: The difference in population or conductance of spin-up and spin-down electrons at the Fermi level in a magnetic material.

Coherent tunnelling: Quantum tunnelling process in which electron wavevector and symmetry are preserved across the barrier, leading to high TMR.

Antiferromagnet: A magnetic material whose neighbouring spins align antiparallel, resulting in zero net magnetisation but supporting ordered spin textures.

Cluster magnetic octupole: A higher-order multipole moment arising from non-collinear spin arrangements in antiferromagnets, breaking time-reversal symmetry.

Grain boundary: Interface between crystalline regions in a polycrystalline film, which can introduce electronic states that shunt tunnelling currents.

References

1. Octupole-driven magnetoresistance in an antiferromagnetic tunnel junction. Nature (2023).
2. Atomic structure and electronic properties of MgO grain boundaries in tunnelling magnetoresistive devices. Scientific Reports (2017).
3. 631% room temperature tunnel magnetoresistance with large oscillation effect in CoFe/MgO/CoFe(001) junctions. Applied Physics Letters (2023).
4. Tunneling magnetoresistance materials and devices for neuromorphic computing. Materials Futures (2023).
5. Antiferromagnetic tunnel junctions for spintronics. npj Spintronics (2024).