Accepted
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Abstract +
The 1 K cryogenic system can provide a stable and necessary low-temperature environment for some fields such as quantum computing, condensed matter physics research, and cryogenic scientific instruments. Specifically, in the field of basic research, 1 K is an ideal condition for studying quantum phenomena in low-temperature physics (such as quantum Hall effect, topological phase transition, etc.); in the field of technical applications, 1 K is a necessary condition for some quantum devices (such as superconducting quantum interferometers, single-photon detectors, etc.) to achieve high-sensitivity operation; in the field of ultra-low temperature technology, 1 K is the pre-cooling stage of refrigeration technologies such as dilution refrigerators, and is the basis for further achieving mK temperature ranges and lower temperatures. At present, most domestic 1 K systems use GM cryocoolers for pre-cooling. The system has certain difficulties in achieving lower vibration control, lower electrical noise interference, lower pre-cooling temperature and higher liquefaction efficiency. The 1 K systems based on pulse tube cryocoolers pre-cooling have inherent advantages in solving these problems. This paper first developed a 4 K GM-type pulse tube cryocooler, using a domestic helium compressor and a developed rotary valve, and redesigned the cold-end heat exchanger and the room-temperature phase shifters, achieving a minimum cooling temperature of 2.14 K, and providing 1.5 W@4.2 K and 45 W@45 K cooling capacity simultaneously. Based on the self-developed pulse tube cryocooler as the pre-cooling stage, a 1 K cryogenic system was further constructed. By designing key components such as JT flow resistance, combined thermal switch, and anti-superflow structure, a minimum cooling temperature of 1.1 K was obtained, and a cooling capacity of 100 mW can be provided at 1.6 K. This study has laid an important foundation for the subsequent development of dilution refrigerators with larger cooling capacity.
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Abstract +
Complex multi-body interactions between ions and surrounding charged particles exist in hot and dense plasmas. It will screen the Coulomb potential between the nucleus and electrons, and significantly change the atomic structures and dynamic properties. This will further affect macroscopic plasma properties such as radiation opacity and the equation of state. Based on the atomic-state-dependent (ASD) screening model, we investigate the photoionization dynamic of Fe25+ ion in hot and dense plasmas. The photoionization cross section for all transition channels and total cross sections of n ≤ 2 states for Fe25+ are studied in detail, as well as the low-energy characteristics induced by plasma screening. Compared to the classical Debye Hückel model, the ASD model incorporated the degeneracy effects by inelastic collision processes, resulting in higher plasma density requirements for bound electrons to merge into the continuum. Near the threshold, the photoionization cross section obeys the Wigner threshold law after considering the screening effect. As the energy increases, the cross sections show low-energy characteristics such as shape resonance, Cooper minimum, low-energy enhancement, and Combet-Farnoux minimum, etc., which can significantly increase or decrease the cross section of the corresponding energy region. For example, the low-energy enhancement in the 2p→εs1/2 channel increases the cross section by several orders of magnitude, drastically changing the properties of the photoelectron spectrum. It is significant to study the low-energy characteristics for understanding the physical properties of the photoionization cross section. Fe is an important element in astrophysics. The cross section results in the middle and high energy region calculated by the ASD model in this paper can provide theoretical and data support for the investigation of hot and dense plasmas in Astrophysics and laboratory situations.
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Abstract +
The Gamma-ray Total Absorption Facility (GTAF), which is composed of 40 BaF2 detection units, is designed to measure the cross section data of neutron radiation capture reaction online, in order to comply the experimental nuclear data sheet. Since 2019, several formidable experiment results have been analyzed and published where we consumed that one of the most important sources of experimental background is initial α particles emitted from the BaF2 crystal, the core component of the detection unit in GTAF, itself.
The development of data analysis algorithms to eliminate the influence of alpha particles in experimental data has become a key aspect, considering the current industrial manufacturing process capabilities, impurities Ra, and its compound, cannot be completely removed from the BaF2. In this paper, to fulfill the need of data collect, online measurement and analysis of neutron radiation cross section, the data acquisition system of GTAF adopts the method of full waveform acquisition, resulting in a substantial amount of data recorded, transmitted, and stored during experiment, which also affects the uncertainty of the cross-section data. The amount of data stored in the online experiment is about 118 MB/s, resulting in a large dead time.
Based on the signal waveform characteristics of the BaF2 detection unit, to address the aforementioned issues, three methods, namely the ratio of fast to total component, pulse width, and time decay constant, are employed to identify and discriminate α particles and γ rays, with the quality factor FOM utilized as an evaluation value and several experiments using three radioactive sources (22Na, 137C, 60Co) used to verify.
Due to the slow components of BaF2 light decay time being about 620 ns, the waveform pulse should essentially return to baseline at approximately 1900 ns to 2000 ns, allowing for the complete waveform of the γ rays signal to be captured at that moment, which might provide the best energy resolution. Therefore, in the online experiment, the integration length for the energy spectrum is chosen to be 2000 ns in this paper.
The quality factors of fast total component ratio (fast component 5 ns, total component 200 ns) method are 1.19~1.41, pulse width (10% peak) method are 0.94~1.04, and time attenuation constant method are 0.93~1.07. Through the quantitative analysis of quality factor and the comparison of energy spectrum, it is determined that the fast total component ratio method has the best effect, which can effectively remove the background of α particles.
The next step is to upgrade the online experimental data acquisition system to reduce the amount of experimental data and the uncertainty of cross section data. The experiment data need to be recorded should be the crossing threshold time for each signal waveform (for the time-of-flight method) and the amplitude integration value of 5 ns after the threshold (for the fast component), of 200 ns after the threshold (for the total component) and of 2000 ns (for the energy), as well as the related detection unit number. These mentioned information should be sufficient to complete the online experimental data online processing, including processing the α particle background and (n,γ) reactions data. It is estimated that the data acquisition rate of the upgraded system will decrease from 118 MB/s to 24 MB/s, which can significantly reduce the dead time of the data acquisition system and thereby improve the accuracy of cross section data.
The development of data analysis algorithms to eliminate the influence of alpha particles in experimental data has become a key aspect, considering the current industrial manufacturing process capabilities, impurities Ra, and its compound, cannot be completely removed from the BaF2. In this paper, to fulfill the need of data collect, online measurement and analysis of neutron radiation cross section, the data acquisition system of GTAF adopts the method of full waveform acquisition, resulting in a substantial amount of data recorded, transmitted, and stored during experiment, which also affects the uncertainty of the cross-section data. The amount of data stored in the online experiment is about 118 MB/s, resulting in a large dead time.
Based on the signal waveform characteristics of the BaF2 detection unit, to address the aforementioned issues, three methods, namely the ratio of fast to total component, pulse width, and time decay constant, are employed to identify and discriminate α particles and γ rays, with the quality factor FOM utilized as an evaluation value and several experiments using three radioactive sources (22Na, 137C, 60Co) used to verify.
Due to the slow components of BaF2 light decay time being about 620 ns, the waveform pulse should essentially return to baseline at approximately 1900 ns to 2000 ns, allowing for the complete waveform of the γ rays signal to be captured at that moment, which might provide the best energy resolution. Therefore, in the online experiment, the integration length for the energy spectrum is chosen to be 2000 ns in this paper.
The quality factors of fast total component ratio (fast component 5 ns, total component 200 ns) method are 1.19~1.41, pulse width (10% peak) method are 0.94~1.04, and time attenuation constant method are 0.93~1.07. Through the quantitative analysis of quality factor and the comparison of energy spectrum, it is determined that the fast total component ratio method has the best effect, which can effectively remove the background of α particles.
The next step is to upgrade the online experimental data acquisition system to reduce the amount of experimental data and the uncertainty of cross section data. The experiment data need to be recorded should be the crossing threshold time for each signal waveform (for the time-of-flight method) and the amplitude integration value of 5 ns after the threshold (for the fast component), of 200 ns after the threshold (for the total component) and of 2000 ns (for the energy), as well as the related detection unit number. These mentioned information should be sufficient to complete the online experimental data online processing, including processing the α particle background and (n,γ) reactions data. It is estimated that the data acquisition rate of the upgraded system will decrease from 118 MB/s to 24 MB/s, which can significantly reduce the dead time of the data acquisition system and thereby improve the accuracy of cross section data.
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Abstract +
When the wall temperature of the thermal protection or insulation materials on the surface of an aircraft exceeds their tolerance limits under the heating of supersonic aerodynamic heat energy, degradation damage phenomena such as high-temperature thermochemical ablation and mechanical erosion will occur in the surface area. The ablation diffusion products (ablation particles) generated are ejected into the surrounding plasma flow field and suspended around the aircraft, forming a hypersonic plasma flow field with ablation diffusion substances. The presence of ablation diffusion substances can significantly affect the physical and electromagnetic characteristics of the original plasma flow field. To address this problem, this study establishes a coupled electromagnetic model of an ablative plasma flow field surrounding a blunt-nosed cone aircraft and analyzes the antenna radiation characteristics in the wake region of the ablative flow field. The research methodology consists of several key steps: Firstly, the plasma flow field around the blunt-nosed cone is simulated using ANSYS FLUENT, a computational fluid dynamics (CFD) software. This step provides the fundamental flow field parameters (e.g., electron density, temperature, and pressure distributions). Secondly, ablation particles, generated from thermal protection material degradation, are uniformly dispersed into the plasma flow. Then, the ablative plasma flow field is obtained. Thirdly, an X-band horn antenna is designed in ANSYS HFSS and loaded into the center of the wake region of the ablative plasma flow field. Based on above models, the ray-tracing method is employed to quantitatively evaluate the attenuation of antenna radiation as it propagates through the wake region. The numerical results demonstrate that the plasma flow field enveloping the aircraft induces significant attenuation of antenna radiation energy. More noteworthy is that the presence of ablation particles within the flow field substantially amplifies this energy dissipation effect. Both the ablation particle density and size distribution are identified as dominant factors controlling radiative energy loss, exhibiting proportional relationships with the incident field's attenuation. The study systematically proves the impact of ablation particle density and size on initial field energy attenuation. This research can provide a reference for addressing the electromagnetic wave propagation underlying the information transmission bottleneck of near-space hypersonic aircraft. It also offers a theoretical basis for further in-depth research on technologies such as target detection, identification, thermal protection/insulation materials, and system design of hypersonic aircraft.
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Abstract +
Divertor detachment is a critical technique for managing the thermal load on the divertor of the HL-3 tokamak, a key device in magnetic confinement fusion research. However, existing studies on detachment have largely overlooked the complex multi-species particle dynamics in the scrape-off layer (SOL) and divertor regions, particularly the interactions involving hydrogen isotopes (e.g., deuterium), externally injected impurities (e.g., neon), and intrinsic impurities (e.g., carbon). This study aims to address this gap by employing the newly developed multi-species particle transport code SD1D to investigate the effects of carbon impurities and neutral particles on two detachment scenarios in HL-3: plasma density ramp-up and neon injection into the divertor.
The SD1D code models the transport, collision, and radiation processes of various particles, including deuterium ions, atoms, and molecules, as well as carbon and neon impurities, along the magnetic field lines from the SOL upstream to the divertor target. The study focuses on understanding how carbon impurities and neutral particles influence the detachment mechanisms under different conditions.
The results reveal that carbon impurities generated in the divertor significantly enhance detachment in the density ramp-up scenario by increasing the density of deuterium atoms, molecules, and ions near the target plate, thereby boosting the total radiation power. This effect lowers the density threshold required for detachment and reduces the peak current on the target plate. However, carbon impurities have a minimal impact on detachment achieved through neon injection, as they do not significantly alter the density of deuterium species or the total radiation power in this scenario.
Furthermore, the study highlights the distinct roles of neutral particles in the two detachment mechanisms. In the density ramp-up scenario, the increased plasma density promotes the recycling process in the divertor, generating a substantial population of neutral particles. The energy and momentum losses resulting from plasma-neutral interactions are crucial for achieving detachment. In contrast, neon injection directly reduces the saturation current on the target plate, suppressing the recycling process and diminishing the importance of neutral particles.
In conclusion, this work demonstrates that carbon impurities play a significant role in facilitating detachment during plasma density ramp-up but have limited influence on detachment via neon injection. The findings underscore the importance of considering multi-species particle dynamics, including neutral particles and impurities, in understanding and optimizing divertor detachment strategies. Future work will involve validating the SD1D model against experimental data from HL-3 to further refine its predictive capabilities.
The SD1D code models the transport, collision, and radiation processes of various particles, including deuterium ions, atoms, and molecules, as well as carbon and neon impurities, along the magnetic field lines from the SOL upstream to the divertor target. The study focuses on understanding how carbon impurities and neutral particles influence the detachment mechanisms under different conditions.
The results reveal that carbon impurities generated in the divertor significantly enhance detachment in the density ramp-up scenario by increasing the density of deuterium atoms, molecules, and ions near the target plate, thereby boosting the total radiation power. This effect lowers the density threshold required for detachment and reduces the peak current on the target plate. However, carbon impurities have a minimal impact on detachment achieved through neon injection, as they do not significantly alter the density of deuterium species or the total radiation power in this scenario.
Furthermore, the study highlights the distinct roles of neutral particles in the two detachment mechanisms. In the density ramp-up scenario, the increased plasma density promotes the recycling process in the divertor, generating a substantial population of neutral particles. The energy and momentum losses resulting from plasma-neutral interactions are crucial for achieving detachment. In contrast, neon injection directly reduces the saturation current on the target plate, suppressing the recycling process and diminishing the importance of neutral particles.
In conclusion, this work demonstrates that carbon impurities play a significant role in facilitating detachment during plasma density ramp-up but have limited influence on detachment via neon injection. The findings underscore the importance of considering multi-species particle dynamics, including neutral particles and impurities, in understanding and optimizing divertor detachment strategies. Future work will involve validating the SD1D model against experimental data from HL-3 to further refine its predictive capabilities.
Abstract +
H2 molecule and their isotopes represent one of the modern clean energy sources. It is imperative to understand their thermodynamic properties to comprehend their behavior under various conditions and facilitate their deeper applications. This paper utilizes the extended improved multiparameter exponential-type potential (EIMPET) combined with the quantum statistical ensemble theory to investigate and analyze the thermodynamic properties of H2 and HD molecules.
Firstly, reliable energy level data for molecules were obtained using the EIMPET potential. Subsequently, the one-dimensional Schrödinger equation was solved with the LEVEL program to determine the rovibrational energy levels of the molecules. Finally, the quantum statistical ensemble theory was integrated to determine the partition functions, molar heat capacity, molar entropy, molar enthalpy, and reduced molar Gibbs free energy of H2 and HD over the temperature range of 100-6000 K. The calculation results indicate that compared with IHH potential and IMPET potential, the EIMPET potential is closer to RKR data. A comparison of the calculated thermodynamic properties of the molecules revealed that the EIMPET potential-based method results agree well with the NIST database. Specifically, for H2, the root mean square errors (RMS) for Cm(T), Sm(T), Gr(T), and ΔHr(T) were were 0.6894 J•K-1•mol-1, 0.3824 J•K-1•mol-1, 0.1754 J•K-1•mol-1, and 0.9586 kJ•mol-1, respectively, while for HD, the RMS values were 0.3431 J•K-1•mol-1, 0.1443 J•K-1•mol-1, 0.0495 J•K-1•mol-1, and 0.4863 kJ•mol-1, respectively, all of these results are superior to that obtained using IMPET potential, and overall superior to IHH potential. These findings demonstrate the advantages of the EIMPET potential in calculating the thermodynamic properties of diatomic gas molecules and its practical applications, providing a foundation for subsequent research on the thermodynamic properties of triatomic molecules.
Firstly, reliable energy level data for molecules were obtained using the EIMPET potential. Subsequently, the one-dimensional Schrödinger equation was solved with the LEVEL program to determine the rovibrational energy levels of the molecules. Finally, the quantum statistical ensemble theory was integrated to determine the partition functions, molar heat capacity, molar entropy, molar enthalpy, and reduced molar Gibbs free energy of H2 and HD over the temperature range of 100-6000 K. The calculation results indicate that compared with IHH potential and IMPET potential, the EIMPET potential is closer to RKR data. A comparison of the calculated thermodynamic properties of the molecules revealed that the EIMPET potential-based method results agree well with the NIST database. Specifically, for H2, the root mean square errors (RMS) for Cm(T), Sm(T), Gr(T), and ΔHr(T) were were 0.6894 J•K-1•mol-1, 0.3824 J•K-1•mol-1, 0.1754 J•K-1•mol-1, and 0.9586 kJ•mol-1, respectively, while for HD, the RMS values were 0.3431 J•K-1•mol-1, 0.1443 J•K-1•mol-1, 0.0495 J•K-1•mol-1, and 0.4863 kJ•mol-1, respectively, all of these results are superior to that obtained using IMPET potential, and overall superior to IHH potential. These findings demonstrate the advantages of the EIMPET potential in calculating the thermodynamic properties of diatomic gas molecules and its practical applications, providing a foundation for subsequent research on the thermodynamic properties of triatomic molecules.
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Abstract +
The Compton camera for γ-ray imaging has the advantages of light weight, high detection efficiency and wide imaging energy range. However, it is difficult for the detection system to distinguish the Compton scattering event and scattering photon absorption event, which results in erroneous image reconstruction. In this paper, a simulation model of Compton camera based on a three-dimensional position-sensitive CdZnTe detector is constructed using GEANT4 program. The detection of characteristic γ-ray from a far-field 137Cs point-like source is simulated. The location of the interaction and energy deposition in the detector are recorded by means of event-by-event. The Compton scattering angle of effective Compton scattering events and imaging of the radioactive source are reconstructed using the simple back-projection algorithm which is a suitable image reconstruction algorithm for real-time imaging scenes. The effect of event sequence reconstruction on the imaging resolution and its improvement are investigated. The results show that the impact of incorrect sequence events on imaging is mainly in the region within 30° from the source position, resulting in a decrease in the density of the image point distribution at the source position. Incorrect reconstructed image points are generated near the source position and form a ring at 26°. The percentage of correctly sequenced events increase to 82% using Compton edge test and simple comparison method based on the deposited energy for sequencing events. The density of the image point distribution at the source location is improved by 47%, and the incorrect reconstruction of the image point distribution near the source location is greatly suppressed, resulting in an improved imaging resolution. The results provide support for the design of Compton camera and the optimization of image reconstruction.
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Abstract +
The manta ray is a large marine species that exhibits both highly efficient gliding and agile flapping capabilities. It can autonomously switch between various motion modes, such as gliding, flapping, and group swimming, based on ocean currents and seabed conditions. To address the computational resource and time constraints of traditional numerical simulation methods in modeling the manta ray's 3D large-deformation flow field, this study proposes a novel generative artificial intelligence approach based on a denoising probabilistic diffusion model (surf-DDPM). This method predicts the surface flow field of the manta ray by inputting a set of motion parameter variables. Initially, we establish a numerical simulation method for the manta ray’s flapping mode using the immersed boundary method and the spherical function gas kinetic scheme (IB-SGKS), generating an unsteady flow dataset comprising 180 sets under frequency conditions of 0.3-0.9 Hz and amplitude conditions of 0.1-0.6 body lengths. Data augmentation is then performed. Subsequently, a Markov chain for the noise diffusion process and a neural network model for the denoising generation process are constructed. A pretrained neural network embeds the motion parameters and diffusion time step labels into the flow field data, which are then fed into a U-Net for model training. Notably, a Transformer network is incorporated into the U-Net architecture to enable handling of long-sequence data. Finally, we examine the impact of neural network hyperparameters on model performance and visualize the predicted pressure and velocity fields for multi-flapping postures that were not included in the training set, followed by a quantitative analysis of prediction accuracy, uncertainty, and efficiency. The results demonstrate that the proposed model achieves fast and accurate predictions of the manta ray’s surface flow field, characterized by extensive high-dimensional upsampling. The minimum PSNR and SSIM values of the predictions are 35.931 dB and 0.9524, respectively, with all data falling within the 95% prediction interval. Compared with CFD simulations, the AI model enhances the prediction efficiency of single-condition simulations by 99.97%.
, , Received Date: 2024-12-15
Abstract +
The precise spectroscopy of few-electron atoms plays a pivotal role in advancing fundamental physics, encompassing the verification of quantum electrodynamics (QED) theory, the determination of fine-structure constants, and the exploration of nuclear properties. With the rapid development of precision measurement techniques, the demand for atomic structure data has evolved from mere confirmation of existence to the pursuit of unprecedented accuracy. To meet the growing needs for precision spectroscopy experiments, we have developed a series of high-precision theoretical methods based on B-spline basis sets, including the non-relativistic configuration interaction (B-NRCI) method, the correlated B-spline basis functions (C-BSBFs) method, and the relativistic configuration interaction (B-RCI) method. These methods leverage the unique properties of B-spline functions, such as locality, completeness, and numerical stability, to accurately solve the Schrödinger and Dirac equations for few-electron atoms. Our methods have yielded significant results, particularly for helium and helium-like ions. Using these methods, we have obtained accurate energies, polarizabilities, tune-out wavelengths, and magic wavelengths. Specifically, we have achieved high-precision determinations of the energy spectra of helium, providing vital theoretical support for related experimental research. Additionally, we have made high-precision theoretical predictions of tune-out wavelengths, paving the way for new tests of QED theory. Furthermore, we have proposed effective theoretical schemes to suppress Stark shifts, thereby facilitating high-precision spectroscopy experiments of helium. The B-spline-basis methods reviewed in this paper have proven exceptionally effective in high-precision calculations for few-electron atoms. These methods have not only provided crucial theoretical support for precision spectroscopy experiments but have also paved new avenues for testing QED. Their ability to handle large-scale configuration interactions and incorporate relativistic and QED corrections makes them versatile tools for advancing atomic physics research. In the future, the high-precision theoretical methods grounded in B-spline basis sets are poised to expand into frontier areas, including quantum state manipulation, nuclear structure property determination, ultracold molecule formation, and new physics exploration, thereby continuously driving the progress of precision measurement physics.
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Abstract +
High-temperature superconductivity, a fundamental topic in condensed matter physics, presents one of the critical scientific challenges of this century. The potential for breakthroughs in this field not only promises to reveal numerous novel quantum phenomena and deepen our understanding of quantum many-body physics but also to significantly drive advancements in experimental techniques, theories, and methodologies in probing correlated quantum systems. More importantly, as a non-perturbative quantum system, high-temperature superconductivity offers an ideal platform and a crucial driving force for systematically establishing non-perturbative quantum field theory. Currently, research on high-temperature superconductivity stands at a critical turning point. Achieving significant breakthroughs requires the development of cutting-edge detection technologies built upon novel concepts, the establishment of innovative theoretical frameworks and methodologies, and insightful elucidation of the physical pictures revealed by experimental findings. Such extensive exploration is vital for unveiling fundamental relationships and identifying the governing principles. By integrating these efforts, we can gain profound insights into the mechanisms of high-temperature superconductivity and significantly expand the horizons of quantum many-body theory.
, , Received Date: 2025-01-20
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, , Received Date: 2025-01-17
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The Rydberg-based microwave detection is an all-optical technology that uses the strong coherent interaction between Rydberg atoms and microwave field. Different from the traditional microwave meter, the Rydberg atomic sensing is a new-type microwave detector that transforms the microwave spectrum into a coherent optical spectrum, and arouses increasingly the interests due to its high sensibility. For this kind of sensor, the coherence effect induced by coupling atoms with microwave plays a key role, and the decoherence may reduce the sensitivity. A multi-level Rydberg atomic scheme with optimized quantum coherence, which enhances both the bandwidth and the sensitivity for 4 GHz microwave sensing, is demonstrated experimentally in this work. The enhanced quantum coherence of Rydberg electromagnetically induced transparency (EIT) and microwave induced Autler-Townes(AT) splitting in EIT windows are shown using optical pumping at D1 line. The enhanced sensitivity at 3.4 GHz with 0.3 GHz bandwidth can be realized, based on the enhanced EIT-AT spectrum. The experimental results show that in the stepped Rydberg EIT system, the spectral width of EIT and microwave field EIT-AT can be narrowed by optical pumping(OP), so the sensitivity of microwave electric field measurement can be improved. After optimizing the EIT amplitude and adding single-frequency microwaves, the sensitivity of the microwave electric field measurement observed by the AT splitting interval is improved by 1.3 times. This work provides a reference for utilizing atomic microwave detection.
, , Received Date: 2025-01-13
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, , Received Date: 2025-01-02
Abstract +
Rare-earth orthoferrites (RFeO3) have received significant attention due to their intricate magnetic interactions and potential applications in ultrafast spintronic devices. Among them, DyFeO3 exhibits rich magnetic phase transitions driven by the interplay between Fe3+ and Dy3+ sublattices. Previous studies mainly focused on temperature-induced spin reorientation near the Morin temperature (TM~50 K), but there has been limited exploration of magnetic phase behavior under external fields above TM. This work aims to systematically investigate the temperature- and magnetic-field-dependent magneto-dynamic properties of a-cut DyFeO3 single crystals, with an emphasis on identifying novel phase transitions and elucidating the underlying mechanisms involving Fe3+-Dy3+ anisotropic exchange interactions. High-quality a-cut DyFeO3 single crystals are grown using the optical floating zone method and characterized by X-ray diffraction (XRD) and Laue diffraction. Time-domain terahertz spectroscopy (THz-TDS) coupled with a superconducting magnet (0–7 T, 1.6–300 K) is employed to probe the ferromagnetic resonance (FM) and antiferromagnetic resonance (AFMR) modes. By analyzing the frequency trends in the spectra, the response of internal magnetic moments to external stimuli can be inferred. In the zero magnetic field experiment, it is found that the temperature induced spin reorientation (Γ4→Γ1) occurs at Morin temperature(~50 K) with temperature decreasing. A broadband electromagnetic absorption (0.45–0.9 THz) occurs below 4 K, which is attributed to electromagnons activated by broken inversion symmetry in the Dy3+ antiferromagnetic state. Above the Morin temperature, the absorption spectra of the sample are measured at constant temperatures (70, 77, 90, 100 K) and magnetic fields ranging from 0 to 7 T. The experimental results show that with the increase of magnetic field, a new magnetic phase transition occurs (Γ 4 → Γ 24 → Γ 2 → Γ 24 → Γ 2 ), and the critical magnetic field of the phase transition varies with temperature. The phase transitions arise from the competition between external magnetic fields and internal effective fields generated by anisotropic Fe3+-Dy3+ exchange. These findings contribute to the further understanding of the magnetoelectric effects in RFeO3 systems and provide a roadmap for using field-tunable phase transitions to design spin-based devices .
, , Received Date: 2025-01-17
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