Journal of Low Temperature Physics最新文献

Nanocrystalline Ni_0.9−xZn_0.1Co_xFe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) ferrites were synthesized via the sol–gel method, yielding a cubic single-phase spinel structure (Fd−3m), as confirmed through Rietveld refinement. The crystallite size was observed to increase from 7 to 10 nm with higher Co substitution. Magnetic characterization revealed a pronounced dependence on Co concentration, with zero-field-cooled and field-cooled magnetization curves exhibiting bifurcation indicative of magnetic relaxation phenomena. The Ni_0.5Zn_0.1Co_0.4Fe₂O₄ composition exhibited a blocking temperature of 191 K, a Curie temperature of 207 K, and a transition from ferromagnetic ordering at 5 K to superparamagnetic behavior at 300 K. Similarly, Ni_0.3Zn_0.1Co_0.6Fe₂O₄ demonstrated a transition at 251 K with retained ferromagnetic ordering at 5 K. In contrast, Ni_0.1Zn_0.1Co_0.8Fe₂O₄ displayed magnetic irreversibility and a paramagnetic state at 300 K. Raman spectroscopy further corroborated the inverse spinel structure, revealing characteristic vibrational modes at ~ 460 cm⁻¹ and 680 cm⁻¹. These findings underscore the pivotal role of Co substitution in modulating the structural and magnetic properties of Ni_0.9−xZn_0.1Co_xFe₂O₄ nanocrystals, particularly their temperature-dependent magnetic phase transitions. Collectively, the results highlight the influence of Co concentration on the structural and magnetic properties of Ni_0.9−xZn_0.1Co_xFe₂O₄ nanocrystals, particularly their temperature-dependent magnetic transitions.

We investigated the magnetocaloric effect (MCE) and thermodynamic properties of Magnetopolaron embedded in two-dimensional (2D) transition metal dichalcogenides (TMDs) under the canonical ensemble approach. From the results, we found that an increase in magnetic field considerably affects the magnetic moment alignment or brings an additional energy in 2D TMDs monolayers which is responsible for the energy exchange observed. The entropy change or MCE, which is more pronounced in the case of molybdenum and less for tungsten, affects the magnetic state of material. The combined effect of magnetic field and temperature has a great change on the magnetic state of 2D TMDs monolayer materials. The behavior of free energy obtained in the present paper can be used as a characteristic of paramagnetic materials. It comes that all 2D TMDs monolayers studied in the present manuscript present a paramagnetic aspect making them promising candidates for practical applications of magnetic refrigeration.

Using Monte Carlo simulations (MCS), we investigated the magnetic properties and phase diagrams of a hexagonal ferrimagnetic Ising nanotube with a core–shell structure composed of spin-5/2 and spin-2 particles, taking surface dilution into account. Our results revealed several characteristic behaviors. Notably, the concentration of magnetic atoms has a significant influence on both the critical and compensation temperatures. For low values of the exchange interaction ({J}_{s})​, dilution has no effect on the critical temperature. However, a compensation point appears beyond a dilution threshold, observed for (xge 0.6).We also identified critical thresholds for the crystal field anisotropies ({D}_{s})​ and ({D}_{c})​. Below these thresholds, the critical temperature remains nearly constant, then gradually increases and converges toward a saturation value once the thresholds are exceeded. Furthermore, the analysis of hysteresis loops shows that the system’s magnetic response is highly influenced by dilution: the remanent magnetization increases significantly in absolute value as the concentration of magnetic atoms rises from (0.6) to(1.0).

The paper presents the analytic expressions of nearest neighbor distance between two particle, Helmholtz free energy, thermodynamic and structural quantities for hcp crystals on the basis of the statistical moment method (SMM) taking into account of vibrational motion of particles, Helmholtz free energy and thermodynamic quantities for hcp crystals on the basis of the self-consistent field method (SCFM) taking into account of molecular motion. The theoretical results are applied to calculate numerically for hcp-N₂. Some numerical results are compared with experiments and other calculations.

This investigation explores the influence of temperature, radius, Aharonov–Bohm flux, and bandgap energy on the specific heat and magnetocaloric properties of graphene quantum dots. By enforcing the continuity condition of eigenspinors at the graphene quantum dots boundary, an analytical relation is derived, demonstrating the dependence of quantized energy levels on external physical parameters. The specific heat exhibits a Schottky-like anomaly, characterized by an initial rise with increasing temperature, reaching a maximum, followed by a subsequent decline. Enhanced magnetic fields induce a shift in the peak temperature while maintaining a consistent peak magnitude (~ 0.44 J/K). The magnetocaloric potential exhibits a monotonic increase with magnetic field intensity, converging to a saturation value of − 0.7 J/(kg⋅K) at elevated temperatures, where thermal fluctuations dominate. Furthermore, the magnetocaloric response demonstrates greater sensitivity to variations in bandgap energy and magnetic field strength compared to changes in the dot radius and Aharonov–Bohm flux.

The decay dynamics of the (alpha)-group ((^2)D (rightarrow ^4)S transition) of N atoms stabilized in the collection of (hbox {N}_2)–Ne nanoclusters were studied at a temperature of 1.3 K. The variation of the (hbox {N}_2)/Ne ratio in nanoclusters results in substantial changes in the luminescence spectra of the (alpha)-group and in the characteristic decay times for the components of these spectra. In all obtained (alpha)-group spectra, the narrow component at (lambda) = 519.9 nm was observed. The spectroscopic results provide information about the structure of the nitrogen–neon nanoclusters. At elevated temperatures ((approx) 15–36 K), enhanced oxygen (beta)-group luminescence is observed in (hbox {N}_2)–Ne nanoclusters, with a smaller intensity enhancement than those observed within pure (hbox {N}_2) and mixed (hbox {N}_2)–Kr nanoclusters. These results confirm the energy transfer mechanism, in which excited nitrogen molecules formed on the nanocluster surface transfer energy to the stabilized oxygen atoms through the chain of (hbox {N}_2) molecules in a solid matrix.

Thermal resistance and the thermal relaxation time are important physical properties in order to cool down samples at low temperatures. In the case of a dilution refrigerator, the relation between the thermal relaxation time of working fluid in a heat exchanger and the circulation rate should be taken care of. Recently, we reported on the nanopore heat exchanger with dramatically reduced thermal resistance. Experimental results suggested that the thermal relaxation time in the sinter pad is very short (less than 1 s), while the exact value was not determined. In order to verify its relation to the circulation rate, we performed numerical simulations of the thermal relaxation time. The expected monotonic increase with decrease of temperature has been confirmed down to 50 mK. However, at lower temperatures unexpected decrease is found. This unusual behavior is considered due to relatively small thermal resistance of liquid helium compared with the thermal boundary resistance.

Superconducting transition-edge sensor (TES) is one of the sensitive single-photon detectors and possesses the photon-number resolving ability. Almost all of the existing sensitive radiation thermal absorption thin films for the generation of TESs are usually generated by optimizing the material components of the films. Alternatively, in this paper we experimentally demonstrated a flexible and controllable approach to generate the temperature-sensitive superconducting one-component thin film, by using the laser drilling technique. Specifically, we designed the sample by numerical simulation method, fabricated the aluminum (Al) thin film with the optimized pore parameters, and experimentally measured the temperature-dependent resistances in ultra-low thermal noise environments. The measured results indicate that, the resistances of the fabricated porous Al films are highly temperature-sensitive around their superconducting transition-edge regimes, and thus they can be utilized to make the desired TES devices. Although the work temperature of the prepared (mu)-Mux readout circuit does not match the generated TES configuration at present, we argue that the one-component porous films, demonstrated here, may provide an effective approach to make the desired TES device for the experimental implementation of infrared single-photon detection.