Ferromagnetism

Researchers from the University of Maryland, University of California, South Dakota School of Mines and Technology, East China Normal University, KAUST and other institutes recently reported all‑van der Waals multiferroic tunnel junctions (MFTJs) that combine ferromagnetism and ferroelectricity in a single nanoscale spintronic device, enabling four non‑volatile resistance states for multibit memory operation. 

These multistate junctions are realized by vertically stacking three atomically thin crystals: two ferromagnetic electrodes and a ferroelectric tunnelling barrier, all obtained by mechanical exfoliation and then assembled into a clean, defect‑sparse heterostructure. In their prototypical structure, Fe₃GeTe₂/CuInP₂S₆/Fe₃GeTe₂, multilayer Fe₃GeTe₂ serves as the ferromagnetic electrodes, while CuInP₂S₆ (CIPS) provides a ferroelectric spacer with switchable polarization. Because the layers are coupled by van der Waals forces rather than epitaxial bonding, the stack avoids stringent lattice‑matching and chemical‑compatibility constraints that hinder oxide‑based MFTJs and is far less susceptible to interfacial defects and interdiffusion.

Researchers from ETH Zürich, University of Washington, University of Basel and National Institute for Materials Science have demonstrated all-optical control over the spin-valley polarization in twisted molybdenum ditelluride (t‑MoTe₂) homobilayers - a step toward dynamically reconfigurable quantum materials and optically defined topological circuits. The work shows how circularly polarized light can reversibly switch the magnetic orientation of a strongly correlated ferromagnetic state, all without changing the sample temperature.

The experiments, led by Prof. Ataç Imamoğlu (ETH Zürich), Prof. Tomasz Smoleński (University of Basel), and colleagues, exploit a system where two atomically thin MoTe₂ layers are stacked with a small twist angle. This twist creates a moiré superlattice with flat, valley‑contrasting Chern bands, giving rise to highly correlated quantum phases - including Chern insulators and ferromagnetic metals - depending on the electron filling. Because the electronic bands are nearly dispersionless, electron-electron interactions dominate, resulting in spontaneous spin alignment even at cryogenic but steady temperatures.

Researchers from the University of Maryland, King Abdullah University of Science and Technology (KAUST), Nankai University, Cornell University, University of Wisconsin–Madison, Oak Ridge National Laboratory, University of California, University of Tennessee, Air Force Research Laboratory and Rice University recently reported the first experimental realization of non-volatile, electrical control of magnetism in a two-dimensional (2D) material system. The collaborative work demonstrates a robust interferroic magnetoelectric coupling in a van der Waals heterostructure made of atomic layers of ferroelectric CuCrP₂S₆ and ferromagnetic Fe₃GeTe₂ - marking a milestone for 2D multiferroic research and energy-efficient spintronic applications.

At the heart of this work lies the long-standing challenge of stabilizing ferroic order in truly two-dimensional materials. While ferroelectric and ferromagnetic phenomena are both well-established in bulk materials, their coexistence in 2D is difficult to maintain due to depolarization fields and thermal fluctuations that destabilize long-range order. The team overcame these limitations by stacking exfoliated layers of the ferroelectric CuCrP₂S₆ and ferromagnetic Fe₃GeTe₂ with atomically clean interfaces, enabling short-range, interfacial coupling between their ferroic orders.

Researchers from Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Donostia International Physics Center, Leibniz Institute for Solid State and Materials Research Dresden and IMDEA Nanoscience have identified ferromagnetic hexagonal close-packed (hcp) cobalt as a prototypical magnetic nodal-line semimetal that remains robust at room temperature, turning a classic ferromagnet into a highly tunable topological platform for spintronics.

Cobalt has long been regarded as a textbook elemental ferromagnet with a supposedly well-understood band structure, examined in detail for over 40 years. Using spin- and angle-resolved photoemission spectroscopy (spin-ARPES) at the BESSY II synchrotron, the team now observes entangled, spin-polarized bands that cross along extended paths in momentum space without opening an energy gap, even at room temperature. These measurements reveal a dense network of magnetic nodal lines - topological band crossings between two spin-polarized states - that give rise to fast, robust charge carriers central to future information and spin-based technologies.

Researchers at the University of Waterloo recently demonstrated fully electrical, field‑free control of perpendicular magnetization using spin‑orbit torque (SOT) in a low‑symmetry 2D magnet/topological‑insulator heterostructure, paving the way for scalable, energy‑efficient spintronic memory and logic devices.

Stacking the three-fold symmetry of BiSbTe on top of the two-fold symmetry of intercalated-CrTe, the interface only permits a unidirectional symmetry which produces an extremely strong out-of-plane spin torque and can deterministically switch a very hard, perpendicular magnet with ease. Image credit: University of Waterloo  

Modern MRAM and related spintronic memories need dense, robust perpendicular magnetic anisotropy (PMA) bits that can be switched deterministically with low energy consumption, but conventional SOT easily switches only in‑plane moments and typically requires an external bias field to tilt perpendicular spins “up” or “down”. In perpendicular configurations, bits point out of the film plane, which boosts storage density but makes the energy‑efficient, fully electrical control of their state difficult. Standard heavy‑metal/ferromagnet stacks already break out‑of‑plane symmetry and can support in‑plane switching, yet deterministic out‑of‑plane reversal demands breaking additional in‑plane symmetries - usually via an applied magnetic field, which adds circuit complexity, power overhead, and risks cross‑talk between neighboring bits.

Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have partnered with NTNU, the Norwegian University of Science and Technology in Trondheim, and the Institute of Nuclear Physics in the Polish Academy of Sciences to develop a method that facilitates the manufacture of particularly efficient magnetic nanomaterials in a relatively simple process based on inexpensive raw materials. 

Using a highly focused ion beam, they imprint magnetic nanostrips consisting of tiny, vertically aligned nanomagnets onto the materials. This geometry makes the material highly sensitive to external magnetic fields and current pulses.

A team of University of Minnesota researchers recently demonstrated a more efficient way to control magnetization in tiny electronic devices using a material called Ni₄W–a combination of nickel and tungsten. 

The team found that this low-symmetry material produces powerful spin-orbit torque (SOT)—a key mechanism for manipulating magnetism in next-generation memory and logic technologies.

A team of scientists from the Hebrew University of Jerusalem (Israel), the Weizmann Institute of Science (Israel), Pennsylvania State University (U.S.A.), and the University of Manchester (UK) has developed a new way to detect subtle magnetic signals in common metals like copper, gold, and aluminium - using nothing more than light and a clever technique. Their research could pave the way for advances in many fields, from smartphones to quantum computing.

For over a century, scientists have known that electric currents bend in a magnetic field - a phenomenon known as the Hall effect. In magnetic materials like iron, this effect is strong and well understood. But in ordinary, non-magnetic metals like copper or gold, the effect is much weaker. In theory, a related phenomenon - the optical Hall effect - should help scientists visualize how electrons behave when light and magnetic fields interact. But at visible wavelengths, this effect has remained far too subtle to detect. The scientific world has long since believed in its existence, but lacked the tools to measure it.

Researchers from Cornell University, Columbia University and Japan's National Institute for Materials Science have demonstrated direct electrical detection of antiferromagnetic resonance in structures on the few-micrometer scale using spin-filter tunneling in PtTe₂/bilayer CrSBr/graphite junctions in which the tunnel barrier is the van der Waals antiferromagnet CrSBr. 

Ferromagnetic materials have been in use in technologies like magnetic hard drives, magnetic random access memories and oscillators for many years. But antiferromagnetic materials, if only they could be harnessed, hold even greater potential: ultra-fast information transfer and communications at much higher frequencies. Now, the researchers' recent work is a step in that direction. Their work could be beneficial for both detecting and controlling the motion of spins within antiferromagnets using 2D antiferromagnetic materials and tunnel junctions.

Researchers at Osaka University have reported a technique for recovering magnetism in a degraded spintronics device. This method can be applied to improve the robustness of next-generation semiconductor memory.

Spintronics exploits the spin (and charge) of electrons to process and store memory, which is achieved practically by stacking layers of thin material films that behave differently under the influence of a magnetic field. “These devices can be non-volatile, low-power, and robust, but the manufacturing process can cause their magnetic properties to deteriorate,” explains Tomohiro Koyama, lead author of the study. The thin films required for these devices are often formed via sputtering, in which atoms are extracted and deposited onto a substrate. This process, however, can often lead to the magnetic layer becoming oxidized, spoiling its magnetic properties.