Liquid Helium Temperature Range Research Articles

Tailoring the cryogenic magnetism and magnetocaloric effect from Zr substitution in EuTiO3 perovskite

Refrigeration in the liquid helium temperature range provides vital technological support for many scientific frontiers and engineering technologies. The considerable magnetocaloric effect (MCE) makes EuTiO3 a potential candidate for magnetic refrigeration near liquid helium temperature. More interestingly, the magnetic transition from antiferromagnetism to ferromagnetism offers the possibility to tailor the magnetism and improve the MCE of this magnetic system. In this study, the magnetic properties and MCE of EuTi0.875Zr0.125O3 were systematically investigated by first-principles calculation and experiments. The substitution of Zr induces a significant lattice expansion and alters the electronic interactions, leading to a dominance of ferromagnetism in the compound. Remarkable low-field MCE performance has been achieved attributed to the enhanced ferromagnetism and low saturation field. Under the field change of 0–1 T, the maximum magnetic entropy change (−ΔSMmax) and adiabatic temperature change (ΔTadmax) are 17.9 J kg−1 K−1 and 6.1 K, respectively. It is worth noting that the −ΔSMmax of EuTi0.875Zr0.125O3 reaches 10.3 J kg−1 K−1 for a field change of 0–0.5 T, making it one of the best magnetocaloric materials ever reported operating in the liquid helium temperature range.

Design and construction of a refrigerator-cooled adiabatic calorimeter for heat capacity measurement in liquid helium temperature region.

Heat capacity is a fundamental thermodynamic property of a substance. Although heat capacity values and related thermodynamic functions are available for many materials, low-temperature heat capacity measurements, especially for novel materials, can still provide valuable insights for research in physics, chemistry, thermodynamics, and other fields. Reliable low-temperature heat capacity data are typically measured using classical adiabatic calorimeters, which use liquid helium as the refrigerant to provide a cryogenic environment for heat capacity measurements. However, liquid helium is not only expensive but also not easy to obtain, which greatly limits the application of adiabatic calorimetry. In this work, an accurate adiabatic calorimeter equipped with a Gifford-MacMahon refrigerator was designed and constructed for measuring the heat capacity of condensed matter in the temperature range from 4 to 100K. The Gifford-MacMahon refrigerator was utilized to provide a stable liquid helium-free cryogenic environment. A simple mechanical thermal switch assembly was designed to facilitate switching between the refrigeration mode and the adiabatic measurement mode of the calorimeter. Based on the measurement results of standard reference materials, the optimized repeatability and accuracy of heat capacity measurements were determined to be within 0.8% and 1.5%, respectively. The heat capacity of α-Fe2O3 nanoparticles was also investigated with this device. Furthermore, this adiabatic calorimeter only requires electricity to operate in the liquid helium temperature range, which may significantly advance the research on low-temperature heat capacity based on adiabatic calorimetry.

Magnetization dynamics and spin-glass-like origins of exchange-bias in Fe–B–Nb thin films

The phenomenon of exchange bias has been extensively studied within crystalline materials, encompassing a broad spectrum from nanoparticles to thin-film systems. Nonetheless, exchange bias in amorphous alloys has remained a relatively unexplored domain, primarily owing to their inherently uniform disordered atomic structure and lacking grain boundaries. In this study, we present a unique instance of exchange bias observed in Fe–B–Nb amorphous thin films, offering insights into its origins intertwined with the system's spin-glass-like behavior at lower temperatures. The quantification of exchange bias was accomplished through a meticulous analysis of magnetic reversal behaviors in the liquid-helium temperature range, employing a zero-field cooling approach from various initial remanent magnetization states (±MR). At reduced temperatures, the appearance of asymmetric hysteresis, a hallmark of negative exchange bias, undergoes a transformation into symmetric hysteresis loops at elevated temperatures, underscoring the intimate connection between exchange-bias and dynamic magnetic states. Further investigations into the magnetic thermal evolution under varying probe fields reveal the system's transition into a spin-glass-like state at low temperatures. We attribute the origin of this unconventional exchange bias to the intricate exchange interactions within the spin-glass-like regions that manifest at the interfaces among highly disordered Fe-nuclei. The formation of Fe-nuclei agglomerates at the sub-nanometer scale is attributed to the alloy's limited glass-forming ability and the nature of the thin-film fabrication process. We propose that this distinctive form of exchange bias represents a novel characteristic of amorphous thin films.

Magnetocaloric effect in (Tm67Cu33)80Al20 amorphous alloy

The new amorphous alloy with the composition of (Tm67Cu33)80Al20 is designed with the deep binary eutectic composition of Tm67Cu33. The (Tm67Cu33)80Al20 alloy exhibits a fully amorphous structure. As the Cu and Al elements have no magnetic moment, there is only Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic interaction existing in (Tm67Cu33)80Al20 amorphous alloy, leading to its low Curie temperature (TC) (4.4 ± 0.3 K). The peak value of the magnetic entropy change and refrigeration capacity of the (Tm67Cu33)80Al20 amorphous alloy under a magnetic field change of 5 T are 13.4 ± 0.7 J kg−1K − 1 and 174.2 ± 10.5 J kg−1, respectively. The (Tm67Cu33)80Al20 amorphous alloy possesses a relatively high magnetocaloric response compared with that of the reported RE-based alloys with the similar TC. These results indicate that the (Tm67Cu33)80Al20 amorphous alloy could be a promising candidate material for magnetic refrigeration applications in the liquid helium temperature range.

A thermal-coupled/gas-coupled hybrid high-frequency pulse tube cryocooler attaining the liquid-helium temperature

High-frequency pulse tube cryocooler (HPTC) has become an attractive method for space cooling in the liquid-helium temperature range, due to its advantages of potential high efficiency, no moving parts at the cold end, small size, and light weight. However, key problems such as large regenerator losses and insufficient phase-shifting ability challenge it to obtain the liquid-helium temperature. A thermal-coupled/gas-coupled hybrid refrigeration process of HPTC has been designed to obtain the liquid-helium temperature. One HPTC working in the liquid-nitrogen temperature range is used as a pre-cooling stage, and another two-stage gas-coupled structure is employed to obtain liquid-helium temperature. The simulation results show that the lowest no-load temperature is 3.6 K and a cooling power of 84 mW can be provided at 6 K with a total input PV power of 128 W and 10.9 W/77 K pre-cooling power when Helium-4 is chosen as the working gas. An experimental prototype was designed, built, and tested. The simulation and experiment results will be introduced in detail in this paper.

Low-Temperature Magnetic and Magnetocaloric Properties of Manganese-Substituted Gd0.5Er0.5CrO3 Orthochromites

Rare-earth chromites have been envisioned to replace gas-based refrigeration technology because of their promising magnetocaloric properties at low temperatures, especially in the liquid helium temperature range. Here, we report the low-temperature magnetic and magnetocaloric properties of Gd0.5Er0.5Cr1−xMnxO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) rare-earth orthochromites. The Néel transition temperature (TN) was suppressed from 144 K for Gd0.5Er0.5CrO3 to 66 K for the Gd0.5Er0.5Cr0.5Mn0.5O3 compound. Furthermore, magnetization reversal was observed in the magnetization versus temperature behavior of the Gd0.5Er0.5Cr0.6Mn0.4O3 and Gd0.5Er0.5Cr0.5Mn0.5O3 compounds at 100 Oe applied magnetic field. The magnetic entropy change (−∆S) value varied from 16.74 J/kg-K to 7.46 J/kg-K, whereas the relative cooling power (RCP) ranged from 375.94 J/kg to 220.22 J/kg with a Mn ion concentration at 5 T field and around 7.5 K temperature. The experimental results were substantiated by a theoretical model. The present values of the magnetocaloric effect are higher than those of many undoped chromites, manganites and molecular magnets in the liquid helium temperature range.

The State of the Art: Lightweight Cryocoolers Working in the Liquid-Helium Temperature Range

The State of the Art: Lightweight Cryocoolers Working in the Liquid-Helium Temperature Range

Physical Mechanisms Based Constitutive Model of Creep in Irradiated and Unirradiated Metals at Cryogenic Temperatures

The present work describes the physical mechanisms of low temperature creep in irradiated and unirradiated metals. The slow inelastic deformations of solids under stress below the yield stress of the material are considered. For the problem of creep at cryogenic temperatures, the classical creep models are not enough. The purpose of this paper is to formulate a physically-based constitutive model of creep for irradiated materials at cryogenic temperatures (liquid nitrogen 77 K, liquid helium, 4.2 K) based on the idea that a dislocation held up by a potential barrier can pass through it owing to the quantum-mechanical tunnelling effect. The problem is novel in the context of recognition of physical mechanisms taking place at cryogenic temperatures leading to the evolution of radiation induced defects under mechanical loads. Creep produced by the expansion of irradiation induced dislocation loops is considered. The kinetic law for evolution of a dislocation loop is proposed using the mechanism of development of a dislocation line over Peierls stress hills. Also, creep produced by the elastic interaction of a radiation induced point defects with existing dislocations in materials is regarded. Predicted creep rate behaviour as a function of stresses and dpa are presented which would need to be validated with data in irradiated materials. Moreover, the new constitutive model of low temperature creep in unirradiated materials is formulated. The Glen-Mott quantum mechanical dislocation tunnelling effect allows extending the theory to the liquid helium temperature range. For this case of unirradiated materials, the creep curves validated experimentally for copper and stainless steel in cryogenic temperature are shown.

Electron paramagnetic resonance of lanthanides.

Many applications of lanthanides exploit their electron spin relaxation properties. Double electron-electron measurements of distances are possible because of the relatively long relaxation times of Gd3+. Relaxation enhancement measurements of distance are possible because of the much shorter relaxation times of other lanthanides. Magnetic resonance imaging contrast agents use the long relaxation time of the S-state Gd3+ ion, and NMR shift reagents use the fast relaxation of selected other lanthanides. Other than Gd3+ and the isoelectronic Eu2+ ion, spin relaxation of the lanthanides is so fast that their EPR spectra can be observed only in the liquid helium temperature range. In this chapter the EPR properties of each of the lanthanides is briefly summarized, with an emphasis on electron spin relaxation.

340 GHz Double-Sideband Mixer Based on Antenna-Coupled High-Temperature Superconducting Josephson Junction

Wireless communication and sensing are moving from microwave, millimeter-wave into the terahertz (THz) frequency regime to meet the fast growing demand of ultrahigh data-rate communications and super resolution imaging. Faced with severe atmospheric absorption attenuation and the lack of power efficient transmitting source at the higher band, ultrasensitive and cost-effective receiver frontend technology is required for advanced THz wireless systems. To date, the most sensitive heterodyne mixers, the key components of frontend receiver systems, are based on low-temperature superconducting materials that operate at liquid helium (4.2 K) temperature range, requiring expensive and bulky cryogenic cooling systems thus hindering them from commercial applications such as wireless communications and sensing. In this article, we present a 340 GHz double-sideband fundamental mixer based on thin-film antenna-coupled high-temperature superconducting (HTS) Josephson junction that operates at a much higher temperature range attainable with smaller and cheaper cryocoolers. Based on our innovative work in terms of advanced device circuit and on-chip antenna designs, accurate parametric simulation analyses, and Josephson junction parameter optimizations, the reported mixer exhibits a measured noise temperature of 470 and 780 K at operating temperatures of 20 and 40 K respectively at 340 GHz, a performance significantly higher than any HTS THz mixers reported to date.

A Separated two stage helium liquefier using a 4 K GM cryocooler

A small-scale helium liquefier using a GM cryocooler (1.5 W @ 4.2 K) is designed and built. The helium gas to be liquefied is precooling by the cryocooler with natural convention loop and the precooling process inside the liquefier is separated to two stages by the first stage cold head of the cryocooler. Liquid nitrogen is used for cooling helium gas before entering the liquefier and cooling the radiation shield as well. The liquefier can start producing liquid helium within 7.5 hours after running from room temperature. A liquefaction rate of 18.57 L/day is obtained at a working pressure of about 115 kPa. Simply designed with high performance makes this helium liquefier appropriate to be used directly with cryostats for scientific experiments of liquid helium temperature range.

Magnetoresistance of composite carbon sensors in strong electric fields in the liquid helium temperature range

A study of how heating current carriers by a pulsed electric field impacts the conductivity and magnetoresistance of carbon composite TVO resistors in the liquid helium temperature range. It is found that heating the carriers in fields of up to 60 V/cm at T = 4.2 K decreases the magnetoresistance by approximately 4 times, while preserving a relatively high temperature dependence of resistance. In fields greater than 400 V/cm in the 4–20 K range the TVO resistor stops depending on temperature. The results are explained using the hopping conduction model among randomly grouped carbon nanograins. The possibility of decreasing the margin of error when measuring the temperature using TVO resistors in the magnetic field is demonstrated.

The cost of coolers for cooling superconducting devices at temperatures at 4.2 K, 20 K, 40 K and 77 K

This author and other authors have written papers concerning the cost of refrigeration as a function of the refrigeration delivered. These papers have included small coolers as well. The lowest temperature range from 3.8 K to 4.7 K (the liquid helium temperature range) is covered using coolers that have two stages. The use of magnets and power equipment that use MgB2 conductors and HTS conductors have spurred the development of coolers that work well temperature ranges from 15 K to 30 K (hydrogen temperature applications), HTS conductors like BSSCO and YBCO for the range from 35 to 50 K and HTS devices from 65 K to 80 K (applications in the liquid nitrogen temperature range). This paper will present some cost data for a number of commercial two-stage and single-stage coolers. This data will be fitted to allow one to estimate the cost of coolers as a function of refrigeration for temperatures of 4.2 K, 20 K, 40 K and 77 K. The efficiency of a large number of coolers over a range of temperatures is also discussed.

Measurements of elastic properties of langatate at liquid helium temperatures for design of ultra low loss mechanical systems

We present full characterisation of acoustic wave devices based on the fully synthetic crystalline material at the liquid helium temperature range required for the design of ultra low loss mechanical systems in many areas of research, including frequency control and fundamental measurements. Temperature coefficients of the effective elastic tensor of Langatate (LGT) in Lagrangian representation are determined for the temperature range of 3.8–15 K. The Lagrangian formalism is mandatory in the analysed situation since the expansion coefficients of the LGT are still unknown at these temperatures. The measurement method involves a set of high-quality resonators of various cut angles and uses measurements of frequency-temperature relations to extract the temperature coefficients of the elastic tensor. In addition, power sensitivity of LGT resonators at cryogenic temperatures is determined and dominant loss mechanism is identified.

In memory of Valentina Abramovna Ioffe (to the 100th anniversary of her birth)

The year 2010 marks the 100th anniversary of thebirth of Professor, Doctor of Physical and Mathematical Sciences, the participant of the Great PatrioticWar, Valentina Abramovna Ioffe, awarded manyorders and medals. Valentina Abramovna Ioffe cameto the Institute of Silicate Chemistry of the Academyof Sciences of the Soviet Union in 1951, immediatelyafter its foundation, and introduced a new directioninto research works performed at the institute, i.e., thestudy of electrical properties of glasses. More recently,she organized a group for the investigation of electricalproperties of dielectrics. In 1963, on the initiative ofthe Director of the Institute N.A. Toropov, the Laboratory of Electronic Processes was created, which,over the next 15 years, was headed by V.A. Ioffe.The first stage of investigations carried out in thelaboratory was concerned with the analysis of mechanisms of charge compensation in the lattice of transition and rareearth metal oxides, as well as with theinfluence of lattice defects on electrical conductivity.This period of the scientific activity of V.A. Ioffe wasdevoted to systematic investigations of dielectric lossesin silica glasses, ferrites, crystalline aluminosilicates,and rareearth aluminates at low temperatures. Iofferevealed a very high sensitivity of dielectric losses tothe degree of depolymerization of the structural glassnetwork. She paid much attention to the study of aluminates of some rareearth elements in which the permittivity reaches 600. More recently, these works wereawarded the medals of the AllUnion Exhibition ofAchievements of National Economy of the SovietUnion.The other side of the V.A. Ioffe activity consisted ininvestigating electrical properties of oxides of variablevalence elements and the mechanism of their conduction. These studies led to the development of the concept of the influence of structural defects on electricalproperties of complex oxides and to the necessity ofstudying the mechanism of defect formation. At thesame time, the range of investigation methodsemployed by V.A. Ioffe was extended by using opticaland magnetic resonance techniques, as well as methods for studying electrical conductivity, thermopower,and permittivity. Electron paramagnetic resonancespectrometers (RE1301, JEOL) and the widelinenuclear magnetic resonance spectrometer were usedover a wide range of temperatures (down to 77 K).Under the supervision of V.A. Ioffe, the procedure forgrowing highquality single crystals of complex oxidesof transition metals and rareearth ions by means ofspontaneous crystallization from own melt, crystallization from solutions in lowmelting salts, and gastransport reactions was implemented at the laboratory.The history of scientific investigations of the laboratory at the first stage of its development wasdescribed by Ioffe in [1].The second stage (since 1978) has been associatedwith the advent of a younger generation, who creatednew experimental and theoretical capabilities for investigations, i.e., the study in the range of liquidheliumtemperatures (down to 4 K) on the RE1306 spectrometer and the widespread use of computational methodsfor simulating physical properties of materials, whichmade it possible to investigate phase transitions and

Phonon spectroscopy of submicron ceramic materials based on Ce1–x Gd x O2–y solid solutions

The specific features of the kinetic characteristics of subterahertz phonons in ceramic samples based on Ce1–x GdxO2–y electrolyte solid solutions have been investigated in the range of liquid-helium temperatures. It has been demonstrated that the observed anomalies of the transport characteristics of thermal phonons in this system are caused by the formation of structural defects associated with the position of vacancies in the anion sublattice with respect to impurity cations. The activation energy of the two-level system Δ = 8.53 K has been determined from an analysis of the experimental results.

Size effect on the SHG properties of Cu-doped CdI 2 nanocrystals

Because the optically induced second harmonic generation (SHG) is prevented by symmetry in a centrosymmetric material, one needs to form noncentrosymmetric processes in order to observe the SHG. However, one of the efficient ways to enhance the noncentrosymmetricity of a material is to dope it with an appropriate impurity and amount. We grow Cu-doped CdI 2 layered nanocrystal structures from the mixture of CdI 2 and CuI using the standard Bridgman–Stockbarger method and investigate the nano-confined effects by studying the second-order optical effect via the measurements of SHG. The second-order susceptibility for the nanocrystals is calculated and the values at liquid helium temperature range from 0.38 to 0.83 pm V −1 for the thicknesses of 10–0.8 nm respectively. The size dependence demonstrates the nano-sized quantum-confined effect with a clear increase in the SHG with decreasing the thickness of the nanocrystal or crystal temperature. Since the local electron–phonon anharmonicity is described by third-order rank tensors in disordered systems, the SHG is very similar to that one introduced for the third-order optical susceptibility. It has been confirmed by observing the large photoluminescent yield of the pure crystals. The Raman scattering spectra taken for thin nanocrystals confirm the phonon modes originating from interlayer phonons crucially responsible for the observed effects. The obtained results show that the Cu-doped CdI 2 layered nanocrystals are promising materials for applications in optoelectronic nano-devices.

Hall effect and negative magnetoresistance in thin crystals of NbSe3

We have measured the Hall effect and the transverse magnetoresistance in NbSe3 single crystals. In the liquid helium temperature range we observed an absolute negative magnetoresistance (NMR) — the value of the resistance under magnetic field being much lower than that at zero field — in NbSe3 single crystals with a thickness less than 5 μm with the magnetic field oriented in the (b, c) plane. We show that this NMR effect is observed in the magnetic field range in which the Hall constant changes its sign. The results are qualitatively explained by the change of the surface scattering contribution to the magnetoconductance in the magnetic field range near the Hall voltage zero crossing.

Local heating under deformation in the range of liquid-helium temperatures and its measurement with strain gages

The jumplike deformation of stainless steel specimens in liquid helium was shown to be accompanied by local heating with an increase in the temperature to ∼80 K at each serration. Measurements were performed with wire strain gages glued on the specimen and used in the range of small deformations to determine the elastic modulus and yield point. In the range of deformations e ∼ 0.06–0.08, the strain gages were unloaded spontaneously because of the destruction of the glue layer and responded only to variations in the temperature of the specimen at a serration.

Numerical analysis of the superconducting magnet outer vessel of a Maglev train by a structural and electromagnetic coupling method

The harmonic magnetic field generated by the ground coils can cause vibration of the superconducting magnet, which must be reduced as it generates heat in the liquid helium temperature range. Therefore, it is important for the design of lighter magnets to exactly estimate the electromagnetic force on the superconducting magnet. Some causes of the vibration were analyzed by the structural and electromagnetic coupling FEM–BEM method.