Explore the vast range of titles available.

Inflation is the leading theory of the first instant of the universe. Inflation, which postulates that the universe underwent a period of rapid expansion an instant after its birth, provides convincing explanation for cosmological observations. Recent advancements in detector technology have opened opportunities to explore primordial gravitational waves generated by the inflation through “B-mode” (divergent-free) polarization pattern embedded in the cosmic microwave background anisotropies. If detected, these signals would provide strong evidence for inflation, point to the correct model for inflation, and open a window to physics at ultra-high energies. LiteBIRD is a satellite mission with a goal of detecting degree-and-larger-angular-scale B-mode polarization. LiteBIRD will observe at the second Lagrange point with a 400 mm diameter telescope and 2622 detectors. It will survey the entire sky with 15 frequency bands from 40 to 400 GHz to measure and subtract foregrounds. The US LiteBIRD team is proposing to deliver sub-Kelvin instruments that include detectors and readout electronics. A lenslet-coupled sinuous antenna array will cover low-frequency bands (40–235 GHz) with four frequency arrangements of trichroic pixels. An orthomode-transducer-coupled corrugated horn array will cover high-frequency bands (280–402 GHz) with three types of single frequency detectors. The detectors will be made with transition edge sensor (TES) bolometers cooled to a 100 milli-Kelvin base temperature by an adiabatic demagnetization refrigerator. The TES bolometers will be read out using digital frequency multiplexing with Superconducting QUantum Interference Device (SQUID) amplifiers. Up to 78 bolometers will be multiplexed with a single SQUID amplifier. We report on the sub-Kelvin instrument design and ongoing developments for the LiteBIRD mission.

Demagnetization is an essential step for the demounting and safe handling of end-of-life NdFeB. Thermal demagnetization in air is a straightforward option to demount adhesive-fixed or segmented magnets. However, this process is suspected to increase the uptake of contaminants like O, C and Zn from coatings and adhesives, potentially degrading the recyclate quality. This study tests the effects of thermal demagnetization in air at 400 °C for 15 to 240 min on variously coated samples with different initial oxidation levels. Furthermore, the possible reversal of the contaminant uptake is explored. Samples with low previous oxidation levels showed significant uptake in oxygen with a minimal diffusion depth, while the uptake depended on the used coating. The best protectiveness was achieved with NiCuNi with an increase in oxygen of only around 30%. Epoxy (up to ~130% O uptake) and Zn coatings (up to ~80% O uptake) disintegrated during the treatment and offered less protection but still made a difference compared to uncoated samples (up to ~220% O uptake). Samples with high initial oxidation levels show no clear tendency towards further oxygen uptake and the carbon uptake is generally low, likely due to contemporary epoxy coatings featuring a passivation underneath as a barrier layer. Zn infiltration, which carried organic debris, was observed. Short demagnetization times proved to be favorable for limiting the depth of the diffusing contaminants. Mechanical coating removal after thermal demagnetization in air can mitigate the contaminant uptake, producing clean, recyclable end-of-life material.

There is a growing demand for refrigeration techniques to reach temperatures below 1 K because these temperatures are critical for a wide range of rapidly developing applications, mainly in the fields of quantum information science, electromagnetic radiation detection, dark matter search and condensed matter physics. A number of methods exist for realizing these temperatures, including 3 He-based cooling ( 3 He evaporation, dilution refrigeration and Pomeranchuk cooling), solid-state cooling (electron demagnetization, nuclear demagnetization and tunnel junction cooling), laser cooling and evaporative cooling among others. Here, this study presents basic principles of these methods and summarizes the corresponding advances in operating temperature ranges and cooling capacities, with the goal of identifying each method’s pros and cons. It is concluded with discussions of the challenges with these methods and key points for improving their performance.

The superconducting heat switch (SCHS) is a critical component in an adiabatic demagnetization refrigerator (ADR) to achieve a temperature down to 50 mK, and its switching performance significantly affects the overall efficiency of the ADR. We have designed a superconducting heat switch utilizing high-purity tin (99.99%) as the superconducting material and conducted experimental testing on its performance. The results show that the superconducting heat switch achieves full conduction under an applied magnetic field of 0.067 T. The thermal conductivities of the designed SCHS in both the normal and superconducting states were measured. The switching ratios were calculated, and the discrepancies between experimental results and theoretical values were analyzed. This heat switch is expected to be primarily used in temperature regions below 500 mK to manage the thermal connection between the single-stage ADR and the 3 He sorption cooler.

Supersolid, an exotic quantum state of matter that consists of particles forming an incompressible solid structure while simultaneously showing superfluidity of zero viscosity 1 , is one of the long-standing pursuits in fundamental research 2 , 3 . Although the initial report of 4 He supersolid turned out to be an artefact 4 , this intriguing quantum matter has inspired enthusiastic investigations into ultracold quantum gases 5 , 6 , 7 – 8 . Nevertheless, the realization of supersolidity in condensed matter remains elusive. Here we find evidence for a quantum magnetic analogue of supersolid—the spin supersolid—in the recently synthesized triangular-lattice antiferromagnet Na 2 BaCo(PO 4 ) 2 (ref. 9 ). Notably, a giant magnetocaloric effect related to the spin supersolidity is observed in the demagnetization cooling process, manifesting itself as two prominent valley-like regimes, with the lowest temperature attaining below 100 mK. Not only is there an experimentally determined series of critical fields but the demagnetization cooling profile also shows excellent agreement with the theoretical simulations with an easy-axis Heisenberg model. Neutron diffractions also successfully locate the proposed spin supersolid phases by revealing the coexistence of three-sublattice spin solid order and interlayer incommensurability indicative of the spin superfluidity. Thus, our results reveal a strong entropic effect of the spin supersolid phase in a frustrated quantum magnet and open up a viable and promising avenue for applications in sub-kelvin refrigeration, especially in the context of persistent concerns about helium shortages 10 , 11 . Evidence for a quantum magnetic analogue of a supersolid appears in a recently synthesized antiferromagnet showing a strong magnetocaloric effect of the spin supersolid phase with potential for applications in sub-kelvin refrigeration.

Magnetic phenomena are ubiquitous in nature and indispensable for modern science and technology, but it is notoriously difficult to change the magnetic order of a material in a rapid way. However, if a thin nickel film is subjected to ultrashort laser pulses, it loses its magnetic order almost completely within femtosecond timescales 1 . This phenomenon is widespread 2 – 7 and offers opportunities for rapid information processing 8 – 11 or ultrafast spintronics at frequencies approaching those of light 8 , 9 , 12 . Consequently, the physics of ultrafast demagnetization is central to modern materials research 1 – 7 , 13 – 28 , but a crucial question has remained elusive: if a material loses its magnetization within mere femtoseconds, where is the missing angular momentum in such a short time? Here we use ultrafast electron diffraction to reveal in nickel an almost instantaneous, long-lasting, non-equilibrium population of anisotropic high-frequency phonons that appear within 150–750 fs. The anisotropy plane is perpendicular to the direction of the initial magnetization and the atomic oscillation amplitude is 2 pm. We explain these observations by means of circularly polarized phonons that quickly absorb the angular momentum of the spin system before macroscopic sample rotation. The time that is needed for demagnetization is related to the time it takes to accelerate the atoms. These results provide an atomistic picture of the Einstein–de Haas effect and signify the general importance of polarized phonons for non-equilibrium dynamics and phase transitions. Ultrafast electron diffraction is used here to reveal in nickel an almost instantaneous, long-lasting population of anisotropic phonons with angular momentum.

Adiabatic demagnetization is currently gaining strong interest in searching for alternatives to 3 He-based refrigeration techniques for achieving temperatures below 2 K. The main reasons for that are the recent shortage and high price of the rare helium isotope 3 He. Here we report the discovery of a large magnetocaloric effect in the intermetallic compound YbPt 2 Sn, which allows adiabatic demagnetization cooling from 2 K down to 0.2 K. We demonstrate this with a home-made refrigerator. Other materials, for example, paramagnetic salts, are commonly used for the same purpose but none of them is metallic, a severe limitation for low-temperature applications. YbPt 2 Sn is a good metal with an extremely rare weak magnetic coupling between the Yb atoms, which prevents them from ordering above 0.25 K, leaving enough entropy free for use in adiabatic demagnetization cooling. The large volumetric entropy capacity of YbPt 2 Sn guarantees also a good cooling power. Magnetocaloric materials are used in adiabatic demagnetization refrigerators to reach extremely low temperature without using Helium. Here, the authors report a large magnetocaloric effect in YbPt2Sn, and show how the properties of this alloy makes it a good magnetocaloric material.

The ultrafast demagnetization dynamics of 3d and 4f spins, respectively, in FeCo and Tb of TbFeCo alloy film are studied independently by employing a dual-color time-resolved magneto-optical Kerr spectroscopy. The demagnetization dynamics of 3d and 4f spins are independently probed, respectively, by 800 and 400 nm light. Two-step demagnetization dynamics are observed for both the 3d and 4f spins under the excitation of 800 nm laser. In particular, the onset of 4f spin dynamics presents a delayed time with respect to the one of 3d spin dynamics. Those results clearly reveal a strong inter-atomic 3d-5d-4f exchange coupling which drives the first-step subpicosecond ultrafast demagnetization process of 4f spins, and a spin(4f)-lattice coupling which drives the second-step slower demagnetization process of 4f spins. A numerical calculation based on four temperature model reproduces the coupling characteristics in the demagnetization dynamics, and reveals the energy evolution dynamics among the different subsystems. These results provide a direct demonstration of strong coupling dynamics between the two spin subsystems in rare earth-transition metal alloy occurring within subpicosecond timescale, and show a new approach for ultrafast control of 4f spins via an indirect excitation.

This study presents the design and single-cycle experimental results of an integrated cryogenic system aimed at achieving 0.1 K operation while minimizing helium-3 usage. The system integrates a commercial Gifford-McMahon (GM) cryocooler, a custom-built sorption cooler, and an adiabatic demagnetization refrigerator (ADR), and is intended to be combined with a single-shot dilution refrigerator (DR). This experiment was conducted to establish a baseline configuration for comparison with all subsequent improvements, focusing solely on evaluating the precooling performance of the ADR system with the added DR components. The ADR cycle experiments showed that the DR components were cooled to approximately 3.6 K, but quickly reheated due to significant heat ingress. Additionally, the experiments revealed critical technical limitations: the insufficient cooling power of the GM cryocooler, lack of a radiation shield at 4 K, eddy current heating (ECH), and degradation of the tin-based heat switch after repeated thermal cycling. If these challenges can be resolved, the ADR-based approach is expected to enable stable sub-Kelvin operation down to 0.7 K in compact DR systems for a future cold-cycle.