Epitaxial Growth of Intermetallic MnPt Films on Oxides and Large Exchange Bias

Room-temperature magnetoresistance in an all-antiferromagnetic tunnel junction

Antiferromagnetic spintronics^1-16 is a rapidly growing field in condensed-matter physics and information technology with potential applications for high-density and ultrafast information devices. However, the practical application of these devices has been largely limited by small electrical outputs at room temperature. Here we describe a room-temperature exchange-bias effect between a collinear antiferromagnet, MnPt, and a non-collinear antiferromagnet, Mn₃Pt, which together are similar to a ferromagnet-antiferromagnet exchange-bias system. We use this exotic effect to build all-antiferromagnetic tunnel junctions with large nonvolatile room-temperature magnetoresistance values that reach a maximum of about 100%. Atomistic spin dynamics simulations reveal that uncompensated localized spins at the interface of MnPt produce the exchange bias. First-principles calculations indicate that the remarkable tunnelling magnetoresistance originates from the spin polarization of Mn₃Pt in the momentum space. All-antiferromagnetic tunnel junction devices, with nearly vanishing stray fields and strongly enhanced spin dynamics up to the terahertz level, could be important for next-generation highly integrated and ultrafast memory devices^7,9,16.

Chemical Potential Switching of the Anomalous Hall Effect in an Ultrathin Noncollinear Antiferromagnetic Metal

The discovery of the anomalous Hall effect in noncollinear antiferromagnetic metals represents one of the most important breakthroughs for the emergent antiferromagnetic spintronics. The tuning of chemical potential has been an important theoretical approach to varying the anomalous Hall conductivity, but the direct experimental demonstration has been challenging owing to the large carrier density of metals. In this work, an ultrathin noncollinear antiferromagnetic Mn₃ Ge film is fabricated and its carrier density is modulated by ionic liquid gating. Via a small voltage of ≈3 V, its carrier density is altered by ≈90% and, accordingly, the anomalous Hall effect is completely switched off. This work thus creates an attractive new way to steering the anomalous Hall effect in noncollinear antiferromagnets.

Electric-Field-Controlled Antiferromagnetic Spintronic Devices

In recent years, the field of antiferromagnetic spintronics has been substantially advanced. Electric-field control is a promising approach for achieving ultralow power spintronic devices via suppressing Joule heating. Here, cutting-edge research, including electric-field modulation of antiferromagnetic spintronic devices using strain, ionic liquids, dielectric materials, and electrochemical ionic migration, is comprehensively reviewed. Various emergent topics such as the Néel spin-orbit torque, chiral spintronics, topological antiferromagnetic spintronics, anisotropic magnetoresistance, memory devices, 2D magnetism, and magneto-ionic modulation with respect to antiferromagnets are examined. In conclusion, the possibility of realizing high-quality room-temperature antiferromagnetic tunnel junctions, antiferromagnetic spin logic devices, and artificial antiferromagnetic neurons is highlighted. It is expected that this work provides an appropriate and forward-looking perspective that will promote the rapid development of this field.

A piezoelectric, strain-controlled antiferromagnetic memory insensitive to magnetic fields

Spintronic devices based on antiferromagnetic (AFM) materials hold the promise of fast switching speeds and robustness against magnetic fields^1-3. Different device concepts have been predicted^4,5 and experimentally demonstrated, such as low-temperature AFM tunnel junctions that operate as spin-valves⁶, or room-temperature AFM memory, for which either thermal heating in combination with magnetic fields⁷ or Néel spin-orbit torque⁸ is used for the information writing process. On the other hand, piezoelectric materials were employed to control magnetism by electric fields in multiferroic heterostructures^9-12, which suppresses Joule heating caused by switching currents and may enable low-energy-consuming electronic devices. Here, we combine the two material classes to explore changes in the resistance of the high-Néel-temperature antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile resistance states at room temperature and zero electric field that are stable in magnetic fields up to 60 T. Furthermore, the strain-induced resistance switching process is insensitive to magnetic fields. Integration in a tunnel junction can further amplify the electroresistance. The tunnelling anisotropic magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a piezoelectric, strain-controlled AFM memory that is fully operational in strong magnetic fields and has the potential for low-energy and high-density memory applications.

Electrically reversible cracks in an intermetallic film controlled by an electric field

Cracks in solid-state materials are typically irreversible. Here we report electrically reversible opening and closing of nanoscale cracks in an intermetallic thin film grown on a ferroelectric substrate driven by a small electric field (~0.83 kV/cm). Accordingly, a nonvolatile colossal electroresistance on–off ratio of more than 10⁸ is measured across the cracks in the intermetallic film at room temperature. Cracks are easily formed with low-frequency voltage cycling and remain stable when the device is operated at high frequency, which offers intriguing potential for next-generation high-frequency memory applications. Moreover, endurance testing demonstrates that the opening and closing of such cracks can reach over 10⁷ cycles under 10-μs pulses, without catastrophic failure of the film.

Electric-field-induced cracks are generally detrimental to functionality of ferroelectric ceramics. Liu et al. use an intermetallic alloy and ferroelectric oxide junction to mediate the reversible formation of cracks at nanoscales, resulting in colossal electroresistance modulation for memory applications.