Wenjie Meng

Imaging measurements of the intrinsic magnetic structures of air-sensitive materials have long posed significant technical challenges. Here, we present a novel magnetic force microscope (MFM) scanning head design that incorporates a rubber O-ring and a threaded sealing assembly to achieve independent, airtight encapsulation of the sample. The fully assembled scanning head exhibits a compact form factor, with an outer diameter of only 24 mm and a total length of merely 80 mm. Based on this design, we have constructed a MFM system tailored for imaging magnetic structures in air-sensitive materials. This MFM system enables operation at magnetic fields of up to 11.7 T and temperatures as low as 5 K. Using this system, we have successfully visualized the evolution of intrinsic magnetic domains in the air-sensitive material VI3 as a function of temperature and applied magnetic field at 5 K. In addition, twin domains arising from structural phase transitions are clearly resolved. Owing to its compact dimensions and high compatibility, the proposed MFM scanning head holds considerable potential for integration into higher-field setups, such as water-cooled bitter magnets, opening avenues for exploring magnetic structures of air-sensitive quantum materials under previously inaccessible experimental regimes.

This work presents an ultra-compact linear piezoelectric motor (PM) for precision positioning in scanning probe microscopy (SPM). The motor consists of a 9-mm-long piezoelectric scanning tube (PST), a trapezoidal zirconia sliding shaft, and a customized beryllium–copper (BeCu) spring ring. The BeCu spring ring provides a stable radial preload and presses the zirconia shaft against the Au-coated inner wall of the PST, forming knife-edge contacts. Microscopic observations show that repeated axial sliding forms a relatively smooth and stable track at the contact interface, suggesting that this interface may help reduce direct wear and improve frictional stability during operation. The developed PM shows a threshold voltage of ∼30 V, a maximum travel range of about 5 mm, and a load-driving capacity exceeding 30 g at 90 V. In a simulated SPM coarse-approach procedure, no obvious parasitic displacement was observed under a 200 V probing waveform at 25 Hz for ∼2 h. Compared with reported piezoelectric-tube-based motors, the proposed PM shows a favorable combination of compact size, low threshold voltage, large travel range, and high load-driving capability. The motor was further used to construct a scanning tunneling microscope (STM), and atomic-resolution imaging of highly oriented pyrolytic graphite was obtained under ambient conditions. These results demonstrate that the proposed PM is suitable for compact SPM systems and other space-constrained nanopositioning applications.

Intertwined superconducting and magnetic orders may give rise to exotic quantum phases^1-7, including field-induced and re-entrant superconductivity^8-10. However, such magnetism-enhanced superconductivity has remained elusive in superconductors with higher transition temperatures^1-3. While infinite-layer nickelates represent a new class of unconventional superconductors^11-20, the impact of rare-earth magnetism on superconducting properties remains largely unexplored. Here, we show that Eu-doped infinite-layer nickelate Sm_0.95-xCa_0.05Eu_xNiO₂ exhibits a magnetic-field-induced re-entrant superconducting phase in the Eu-rich over-doped regime. Zero-resistance transport and high-field diamagnetic screening confirm the superconducting nature of this phase, which emerges after the initial suppression of low-field superconductivity and remains robust across a broad range of temperatures, fields and field orientations. In the same doping range, we observe nonlinear Hall transport and hysteretic magnetoresistance, indicating the unconventional nature of the re-entrant behaviour. While partially consistent with a compensation mechanism between the Eu-derived exchange field and the applied field, our data reveal pronounced deviations from this model at the highest-doping levels. Our findings establish infinite-layer nickelates as a fertile platform for exploring magnetically driven high-field superconductivity in strongly correlated oxides.

Probing microscopic magnetic textures under ultra-high magnetic fields is critical for uncovering emergent quantum phenomena but remains experimentally challenging. Here, we present the first cryogenic magnetic force microscope (MFM) operating at temperatures below 3 K and magnetic fields up to 35 T in a water-cooled resistive magnet. A static exchange-gas helium cryostat provides a stable, chemically inert, and low-vibration cryogenic environment, while a nonmetallic MFM head and high-Q cantilever tips effectively suppress strong-field and mechanical disturbances. The frequency-shift noise is as low as ∼60 mHz at 33 T, well below typical magnetic signal amplitudes (>200 mHz), ensuring sustained high sensitivity throughout field ramping. Using this platform, we imaged field-driven magnetic textures in a multiferroic SrRuO3 film at 2.7 K from 0 to 35 T, revealing robust magnetic-domain behavior locked by ferroelastic domains. This work establishes a powerful platform for real-space imaging of quantum magnetism under extreme conditions.

Rare-earth infinite-layer nickelates are emerging unconventional superconductors, with materials synthesis largely limited to early lanthanide compounds. Here, we report phase-pure samarium-based nickelate thin films on (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (001) substrates, including the first demonstration of Sm_1-xSr_xNiO₂. Co-doped compounds achieve a record-small c-axis parameter (3.26 Å) and superconducting transitions up to 32.5 K, revealing a clear correlation between decreasing c-axis parameter and increasing critical temperature across different rare-earth systems. Angle-dependent magnetoresistance shows a hybrid 2D/3D superconductivity with enhanced rare-earth 5d–Ni 3 d orbital coupling, confirmed by resonant inelastic X-ray scattering. In addition, increasing Eu concentration drives a shift toward 3D superconductivity, and Eu-containing samples exhibit distinctive negative magnetoresistance even in the superconducting state. These findings advocate clear materials design principles for higher transition temperatures and exotic physics in infinite-layer nickelate superconductors through structural engineering of the rare-earth site.

Owing to their unique crystal structures, van der Waals (vdW) materials provide a versatile platform for exploring emergent physical phenomena and enabling next‐generation electronic and spintronic applications. However, the direct correlations between vdW crystal and intrinsic properties, such as magnetism, remain largely unexplored. Here, we demonstrate that a variety of structure‐correlated topological spin textures, characterized by highly regular shapes ranging from triangles to octagons and arranged in periodic patterns, can be induced in vdW crystals. Owing to their well‐resolved boundaries, the entire evolution of the quasiparticle characteristics of the topological structures, including creation, structural distortions, and collision were unambiguously revealed. More importantly, it was found that the topological annihilation occurs in an explosive manner, providing direct confirmation of the quasiparticle nature at the scale of a single magnetic unit. Simulations reveal that their formation arises from the interplay between uniaxial anisotropy and dipolar interactions, further modulated by the lattice background. These findings uncover a previously unrecognized structure‐property relationship in vdW magnets and open avenues for designing and tunning of new topological spin textures.

Achieving in situ rotation of scanning probe microscopes (SPMs) within high-field magnets presents significant technical challenges while remaining essential for micron-scale magnetic anisotropy studies. Here, we demonstrate a compact piezoelectrically driven rotatable magnetic force microscope operable within a standard 50 mm bore cryogen-free superconducting magnet, achieving fields up to 12 T and temperatures down to 2 K. The microscope features a nested coaxial piezoelectric scanning tube (PST) design sharing a common base. In this design, the outer PST provides rigid support for the tip holder, while the inner PST actuates the sample approach. This design effectively attenuates common-mode vibration interference (e.g., from the cryocooler) while expanding the scan range by a factor of 1.74 compared to a single PST structure via reverse-direction scanning, maintaining positioning capability for micron-scale devices. Field-controlled magnetic domain evolution imaging in the 2D van der Waals magnet Fe3GaTe2 across multiple angles confirms system functionality. The results reveal strong out-of-plane anisotropy, manifested by magnetization rotation from out-of-plane to in-plane with an angle, and a characteristic 1/cos θ dependence of the saturation field, dominated by domain wall depinning energy. The vibration-resistant rotating microscope structure in cryogen-free magnets can be extended to broader SPM platforms. In addition, the outer PST enables the inertial drive of the tip holder for millimeter-scale searches.

This work presents the design and construction of a novel ultra-compact piezoelectric motor (PM) that employs a miniaturized piezoelectric tube (PT) measuring 8 mm in length and 3.65 mm in outer diameter. The PT is externally coupled with a curved copper-beryllium (CuBe) spring and a sapphire shaft guided by a zirconia rail to achieve precise linear motion control. The structural design employed the high hardness and wear resistance of sapphire, along with the low-friction properties of zirconia, to ensure precise linear motion and long-term durability. Operating on the inertial stick–slip principle, the PM utilized a modified sawtooth voltage waveform to induce controlled lateral bending of the PT. The spring transmitted motion to the shaft during slow deformation and allowed relative slip during rapid retraction. Experimental results revealed step sizes ranging from 0.1 to 0.8 μm, a threshold voltage of 45 V, and excellent long-term stability (±15 nm drift over 15 h). The design effectively held small loads with high stability, making it well suited for coarse positioning applications. Its compact footprint, simplified assembly, and bidirectional control capabilities underscore its potential for integration into coarse approach mechanisms of scanning tunnel microscopes and other high-resolution instrumentation platforms where space constraints, accuracy, and long-term reliability are critical. This work lays a foundation for future developments in ultra-compact, non-magnetic, application-specific nanopositioning motors.

Manipulating the direction of the magnetic field can induce various intriguing physical phenomena, such as the regulation of nematic phase and disappearance of the charge density wave. Conventional superconducting magnet-based scanning tunneling microscopes (STMs) operate with a perpendicular magnetic field direction to the sample surface, limiting their ability to investigate anisotropy of materials. Some STMs are integrated into vector magnets to achieve in-plane magnetic field conditions; however, these setups typically offer a maximum lateral magnetic field strength of less than 5 T, which is far below the critical magnetic field required for many materials. To explore the anisotropy of materials under in-plane magnetic fields exceeding 20 T, a new STM with small lateral tip–sample junction, which is capable of working in huge vibrational water-cooled magnets, is required. This paper presents an innovative design of such a small lateral size featured STM that is capable of operating under 35 T in-plane magnetic field conditions. The proposed STM utilizes an improved spider drive to drive the tip move in oblique upward direction, with the component of tip motion on the lateral direction being one-fifth of the vertical direction. With the novel design, the lateral size of the STM head is minimized to as small as 15 mm. The high rigidity of an independent scanner is proved by the high eigenfrequencies obtained through finite element analysis. The excellent imaging ability of our new STM are demonstrated by the high-quality atomic images of graphite and NbSe2 acquired under in-plane magnetic fields ranging from 0 to 35 T, illustrating the new STM’s high immunity to the magnetic field conditions. As far as known, this is the first STM capable of atomic imaging at magnetic field up to 35 T and capable of working at both 300 and 1.7 K low temperature; this is also the first water-cooled magnet STM capable of atomic imaging under 35 T magnetic field and huge vibrational conditions. Using this STM, we expect to investigate novel physical phenomena occurring under high in-plane magnetic fields.