Zhan Xu

Ultrafast optical techniques provide unprecedented control over light-spin-lattice interactions in magnetic materials, giving rise to exotic phenomena such as ultrafast demagnetization and all-optical helicity-dependent switching. This indicates the effective modulation of optically excited spin-wave resonance modes in Co ₂ FeSi (CFS) Heusler alloy films via thermal annealing-induced lattice relaxation and local atomic restructuring. In the as-deposited state dominated by macroscopically disordered A2-like configurations, only the magnetostatic surface wave and Kittel mode are observed. Remarkably, thermal annealing promotes short-range chemical ordering and optimizes interfacial spin-pinning conditions, thereby activating additional high-order perpendicular spin standing waves, attributed to enhanced anisotropic fields and modified spin pinning due to improved chemical ordering. Remarkably, despite the emergence of multiple spin wave modes, the magnetic damping factor decreases monotonically with annealing temperature. First-principles calculations indicate that this damping suppression originates from the structural-ordering-induced reduction of spin-flip scattering within the electronic density of states. These findings provide a pathway to engineer low-damping spintronic materials with tailored spin-wave dynamics through controlled structural transitions, offering promising potential for high-frequency magnonic device applications.

As urban underground spaces and infrastructure development accelerate, subsurface elements such as buried pipelines, integrated utility tunnels, subway tunnels, cavity defects, and deep-seated hidden hazards become increasingly intertwined. Consequently, urban target detection is characterized by pronounced scale discrepancies, intense environmental interference, and severely confined operational spaces. The transient electromagnetic method (TEM) is highly valuable for rapid surveys and hazard identification in urban underground spaces owing to its inherent advantages, including non-contact operation, adaptability to hardened pavements, high sensitivity to low-resistivity anomalies, and the ability to probe a broad range of depths. In recent years, research has shifted from improving isolated instrumentation to synergistically optimizing sensing platforms, transmitter–receiver systems, anti-interference methodologies, and imaging interpretation workflows. Specifically, small-loop configurations and high-frequency excitation technologies have improved shallow-sounding capabilities in confined urban spaces; anti-interference techniques have increased data reliability in complex noise environments; and apparent resistivity mapping, virtual wave-field migration, and rapid inversion methodologies have enabled profiling results to transition from qualitative identification to fine-scale interpretation. Concurrently, the evolution of ground-towed, UAV-borne, helicopter-borne, and semi-airborne platforms has progressively endowed urban TEM profiling with continuous, mobile, and scenario-specific operational capabilities. Looking to the future, further technical breakthroughs in urban TEM technology are required to improve shallow-resolution, deep-seated penetration, multi-source interference decoupling, and real-time concurrent imaging.

The optimization of magnetoelectric (ME) sensitivity through microstructural engineering is critical for advanced magnetic sensing technologies. In this study, we systematically investigate the impact of isothermal annealing on the structural, magnetic, and magnetoelectric properties of Metglas/PZT heterostructures. Metglas ribbons were annealed at temperatures ranging from 400 °C to 550 °C to modulate the amorphous-to-nanocrystalline phase evolution. Structural and dynamic analyses via HRTEM and Ferromagnetic Resonance reveal that 450 °C serves as the optimal annealing threshold, yielding a balanced dual-phase architecture with α-Fe nanocrystals (~85.1 nm) embedded in the amorphous matrix. This optimized state achieves a peak ME coefficient (αME) of 41.5 V/cm·Oe and a five-fold enhancement in transient voltage output (108 mV) compared to the pristine state. Furthermore, the 450 °C annealed MEC demonstrates superior performance in practical Magnetic Anomaly Detection (MAD), with a 25-fold increase in spatial sensitivity (28.68 mV/cm) and a 314.3% improvement in angular resolution (1.74 mV/°). Our findings establish a robust correlation between isothermal crystallization kinetics and nonlinear ME response, providing a high-performance framework for weak-field target localization and navigation.

Rapid third-gen semiconductor development drives smaller, more efficient power devices, raising demands for soft magnetic composites (SMCs) high-frequency performance. In this study, FeSiBCuNb nanocrystalline soft magnetic composites (NSMCs) were prepared by adding different amounts of carbonyl iron powder (CIP). The results show that the addition of CIP effectively improves the soft magnetic properties of FeSiBCuNb/CIP NSMCs. When the CIP content increased to 40 wt%, the effective magnetic permeability ( μ _e ) of the NSMCs reached a peak value of 36.6, which was 59.1% higher than that of the NSMCs without CIP. Furthermore, at 20 mT and 1000 kHz, the low core loss ( P _cv ) was 560.3 kW m ⁻³ , with a DC bias performance of 87.2%, which was 33.3% decrease compared to the uncombined state. In addition, the prepared NSMCs can maintain stable soft magnetic properties over a wide temperature range. The FeSiBCuNb/CIP NSMCs prepared in this work have potential applications in high-frequency and high-power electronics.

We report the influence of the capping layer thickness on the effective magnetic damping and the effective spin–orbit torque (SOT) efficiency in Ta/Pt/Co structures via spin-torque ferromagnetic resonance measurements. The SOT efficiency first increases with increasing capping layer thickness ( d _Ta ) , reaching a large value of 0.199 at d _Ta = 1.4 nm, then decreases with further increases in d _Ta . This can be attributed to a competition between the additional SOT field generated by the Rashba–Edelstein effect and the reduced net spin current effect. It has been demonstrated that the magnetic damping factor decreases with increasing capping layer thickness. The high SOT efficiency and low magnetic damping factor suggest the great potential of the Ta/Pt/Co for low-power spintronic technologies.

We reported the structural, static, and dynamic magnetic properties of off-stoichiometric CoFeMn_0.8Si_1.2 (CFMS) quaternary Heusler thin films deposited on MgO substrates with different annealing temperatures ranging from 500 to 750 °C. All films annealed above 500 °C achieve full B2 ordering, with XPS analysis confirming enhanced chemical ordering at 700 °C compared to 500 °C. These films display soft magnetic behavior, with a saturation magnetization of approximately 731.8 emu cc⁻¹ for T_a = 700 °C. Ferromagnetic resonance measurement results demonstrate that as the annealing temperature increases from 500 to 750 °C, the Gilbert damping factor initially decreases and then increases, reaching a minimum of 2.3 × 10⁻³ at 700 °C. First-principles calculations indicate that the off-stoichiometric B2 structure exhibits a considerably diminished density of states at the Fermi energy level. Therefore, the reduced Gilbert damping factor observed in the samples annealed at 700 °C is attributed to the interplay of the low density of states at the Fermi energy level and the high saturation magnetization strength.

The existing detection device for unexploded ordnance (UXO) based on geomagnetic anomaly and electromagnetic induction suffers from issues such as functional separation, large size, and low efficiency due to the constraints of sensors. The centimeter-sized magnetostrictive/piezoelectric composite demonstrates static and dynamic wideband frequency response capabilities for measuring magnetic fields. Here, a novel dual-mode detection method is proposed for receiving magnetic anomalies and transient electromagnetic responses in parallel by the FeNiMoSiB/PZT-5A composite. The transient primary field generated by a transmitting coil can not only cause the target to induce a secondary field, but also drive the operation of the magnetoelectric (ME) composite. The FeNiMoSiB layer excited by a high amplitude field generates nonlinear magnetostriction. Under the magnetic-mechanical-electrical conversion, the ME composite driven by the transient primary field undergoes a step response to output oscillating voltage. Due to the nonlinear ME effect, the oscillating voltage is modulated by the magnetic anomaly, resulting in an amplitude change. The magnetic anomaly information can be obtained by demodulating the resonant voltage signal. After the voltage oscillation ends, it begins to decay. Moreover, the dominant secondary field will hinder the voltage attenuation, and its information can be obtained by analyzing the late attenuation voltage signal. In the experiment, the ferromagnetic metal targets at different depths are detected, and the maximum detection depth is about 1.2m. In field environments, the targets buried at a depth of 0.5m in the soil are successfully located along the survey line, demonstrating good positioning performance.

High effective spin Hall efficiency and low magnetic damping constant are essential to achieve efficient spin-charge conversion for energy-efficient spintronic devices. We report the measurements of effective spin Hall efficiency and magnetic damping constant of Pt_{1- x} Ta _x /CoFeB structures using spin-torque ferromagnetic resonance (ST-FMR) techniques. With the increase of Ta content, the spin Hall efficiency increases and peaks x = 0.15 with the value of θ SH eff = 0.35 , before decreases for further Ta content. This non-monotonic variation is attributed to the interaction between the contribution of the extrinsic skew scattering mechanism and the spin-orbit coupling (SOC). The weakening of the SOC in the Pt_1-x Ta _x layer leads to a decrease in the effective magnetic damping constant with increasing Ta concentration. High-temperature ST-FMR measurements confirm the influence of the Ta concentration on the spin Hall effect and magnetic damping mechanism. Additionally, the decrease in spin mixing conductance and the increase in spin diffusion length leads to a decrease in the interfacial spin transparency.

Under a high amplitude AC excitation field, the magnetostrictive/piezoelectric composite exhibits the nonlinear magnetoelectric (ME) effect. A weak DC/AC magnetic field can be measured by demodulating the odd harmonics generated by the composite structure due to the nonlinear ME effect. The AC excitation magnetic field created by an external signal source will introduce crosstalk noise. Here, a novel method for measuring the weak magnetic field via FeNiMoSiB/PZT-5A/FeNiMoSiB composite excited by step magnetic field is presented. The ME composite excited by the step magnetic field will vibrate at its natural frequency to significantly enhance the ME effect. In addition, the resonance frequency of the ME composite is not affected by the excitation signal, which reduces the noise introduced by the external excitation source. Due to the nonlinear ME effect, the induced ME voltage is modulated by a weak DC/AC magnetic field to be measured. The weak magnetic field signal can be recovered from the ME voltage by the lock-in demodulation method. The ME unit for sensing the magnetic field is designed based on the longitudinal free vibration model excited by a step magnetic field. In the experiment, the step magnetic fields generated by a 2 kHz bipolar square-wave signal are used to excite the ME composite. The sensitivity of 29.77 mV/Oe and linearity error of 0.22% are achieved in the DC magnetic field of -3~3 Oe. The sensitivity to 1~50kHz AC magnetic field to be measured in the flat area is about 37.5 mV/Oe.