Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics - poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness - can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic magnetocaloric YbNi1.6 Sn as an attractive alternative to conventional refrigerants. YbNi1.6Sn retains high entropy into the 100 mK regime and avoids the noble metal constituents of alternative refrigerants. Demagnetisation tests demonstrate that YbNi1.6Sn enables economical and durable alternatives to traditional cooling devices for temperatures reaching below 120 mK. We find that the magnetocaloric properties of this material are facilitated by unusually small Kondo and RKKY interactions, which position YbNi1.6Sn in the extreme local moment limit on the generalised Kondo lattice phase diagram.

Dy(OH) 3 has impressive magnetocaloric performance optimised around 20 K making it suitable for hydrogen liquefaction using magnetic cooling.

The disappearance of a charge-density-wave (CDW) transition in Lu(Pt1-xPdx)2In is thought to be closely linked to a maximum of the superconducting transition temperature in the system. We studied the superstructure and the phonon softening in Lu(Pt0.5Pd0.5)2In by means of neutron and high-resolution inelastic x-ray scattering. A full phonon softening at qCDW = (0.5 0.5 0) with the appearance of superstructure peaks could be clearly identified. This supports the CDW transition to be a continuous transition. The large tail of the superstructure intensity above the CDW transition indicates the importance of critical fluctuations. In general, the observed phonon dispersion relations are quite similar to those predicted by theoretical calculations. However, the softening occurs in a much narrower momentum range than predicted.

The structural transition in Lu(Pt${}_{1\ensuremath{-}x}$Pd${}_{x}$)${}_{2}$In attracts special interest since it can be tuned to zero temperature with the appearance of a superconducting dome around structural quantum criticality. The authors combined inelastic neutron and x-ray scattering measurements to study this structural transition. They determined the low-energy phonon dispersions and detected the relevant phonon branch becoming soft. While theoretical calculations broadly agree with the measured dispersion, a clear non-mean-field behavior is demonstrated at this phase transition, which might be connected with quantum criticality and the superconducting dome.

Determining the origin and consequences of novel phase transitions is a key task in condensed matter physics research. Recently, Lu(Pt1-xPdx)(2)In was discovered to present a very rare case of strongly enhanced superconductivity at a charge density wave (CDW) quantum critical point (QCP). Unlike in most other systems, the CDW transition here is of second-order. By tuning it continuously to absolute zero temperature with variation of an external non-thermal control parameter, for instance chemical composition x or pressure p, a CDW QCP is approached. We present how we succeeded in synthesising large high-quality single crystals of the new Lu(Pt1-xPdx)(2)In series with a large number of intermediate concentrations x. We briefly provide information about the challenges in growing phase-pure single crystals. Furthermore, different anomalies in the temperature dependences of magnetic susceptibility chi(T) and electrical resistivity rho(T) are presented and discussed. The availability of excellent crystals allowed us to investigate the effect of applied hydrostatic pressure p on the CDW and the superconducting state in Lu(Pt0.5Pd0.5)(2)In by rho(T)vertical bar(p) measurements.

We investigated the effect of application of hydrostatic pressure on the charge-density wave (CDW) state in Lu(Pt1−xPdx)2In by electrical-resistivity measurements. In Lu(Pt0.7Pd0.3)2In we find an increase of the CDW transition temperature upon application of pressure, which is not expected based on simple volume arguments, but in line with results of a theoretical work by Kim et al. [Phys. Rev. Lett. 125, 157001 (2020).]. Combining experimental and theoretical results suggests the existence of a CDW quantum critical point in stoichiometric LuPd2In around p ≈ 20 GPa. When a second-order phase transition is continuously suppressed to zero temperature, a quantum critical point (QCP) is formed, where quantum fluctuation may considerably affect physical properties [1, 2]. In the vicinity of a QCP unconventional phases, such as unconventional superconductivity, might emerge eventually [3]. So far, the majority of QCPs has been studied in magnetic materials, most of them in antiferromagnetic[3–5] and only a few in ferromagnetic systems [6, 7]. Only recently a QCP connected to the suppression of charge-density wave (CDW) order and the appearance of a superconducting dome has been established in the rare-earth-based Heusler system Lu(Pt1−xPdx)2In [8]. This finding was quite surprising since most CDW transitions are connected to first-order structural transitions which in many cases can also be suppressed to zero temperature but then exclude the existence of a QCP [9–12]. It makes the system Lu(Pt1−xPdx)2In outstanding among CDW materials. The existence of the CDW QCP was demonstrated in Lu(Pt1−xPdx)2In by utilizing the Pd-concentration as nonthermal external control parameter. One major disadvantage of substitution-tuning is the inevitable introduction of additional atomic disorder in the material which may strongly modify the quantum critical behavior at low temperatures. It is therefore highly desirable to find ways to study the CDW QCP in Lu(Pt1−xPdx)2In in a clean fashion. One possible way to do that is using hydrostatic pressure as external tuning parameter. In Lu(Pt1−xPdx)2In, the CDW state appears for x < xc ≈ 0.58, and TCDW rises up to TCDW = 490 K at x = 0 [8]. LuPt2In has a larger unit-cell volume than LuPd2In which does not order down to the lowest temperatures [8, 13]. Therefore, stoichiometric LuPt2In seems to be the natural choice for a pressure study of a CDW QCP in a clean system. Recently, however, Kim et al. [14] reported a theoretical study on the basis of ab initio density functional theory (DFT) calculations showing that application

We report electron spin resonance of the itinerant ferromagnets LaCrGe3, CeCrGe3, and PrCrGe3. These compounds show well defined and very similar spectra of itinerant Cr 3d spins in the paramagnetic temperature region. Upon cooling and crossing the Cr-ferromagnetic ordering (below around 90 K) strong spectral structures start to dominate the resonance spectra in a quite different manner in the three compounds. In the Ce- and Pr-compounds the resonance is only visible in the paramagnetic region whereas in the La-compound the resonance can be followed far below the ferromagnetic ordering temperature. This behavior will be discussed in terms of the specific interplay between the 4f and 3d magnetism which appears quite remarkable since CeCrGe3 displays heavy fermion behavior even in the magnetically ordered state.

Supporting data for 'Single crystal growth and hydrostatic pressure study of charge density wave quantum critical Lu(Pt1-xPdx)2In' published in Journal of the Physical Society of Japan. The files comprise all raw data included in the paper. That are differential scanning calorimetry, differential thermal analysis, furnace profile, magnetic susceptibility and electrical resistivity data. Furthermore, high quality pictures of Laue pattern and of a single crystal are archived.

Magnetocaloric effect (MCE) has drawn much attention because its magnetic cooling property enables refrigeration without producing noxious gas or using rapidly depleting resources. However, applications for everyday life are yet distant. In addition, we need to understand more about the practical aspect of the MCE. Here, we introduce a phenomenological model to explain the quasi-adiabatic MCE. Correction factors to the equilibrium thermodynamic feature implied by the entropy landscape are devised in analytic forms. To demonstrate the validity of the model, the MCE from two different materials is investigated. The recently discovered metallic paramagnet, YbPt2Sn, shows a linear and reversible MCE which is typical of a paramagnetic system and suitable for cryogenics without 3 He. On the other hand, a complex-phase material, Ce0.5La0.5B6, exhibits a pronounced irreversible MCE especially across a magnetic phase boundary. A term that describes the field induced heating near a phase transition turns out to be essential in resolving the irreversible, non-equilibrium MCE.

An experimental study of the rare-earth intermetallic system LuPt2In reveals a strong enhancement of superconductivity near the charge density wave quantum critical point. This represents an unusual counter-example to cuprates, in which superconductivity and charge density waves tend to compete. Quantum critical points (QCPs), at which a second-order phase transition is continuously suppressed to zero temperature, are currently one of the central topics in solid-state physics1,2. The strong interest emerges from observations of very unusual properties at QCPs such as the onset of unconventional superconductivity (SC)3. While QCPs found at the disappearance of magnetic order are quite common and intensively studied, a QCP that results from a structural transition is scarce and poorly investigated. Here, we report on the observation of a charge density wave (CDW) type of structural ordering in LuPt2In with a second-order transition at TCDW = 490 K. Substituting Pd for Pt suppresses TCDW continuously towards T = 0, leading to a QCP at 58% Pd substitution. We find a strong enhancement of bulk SC just at the QCP, pointing to a new type of interaction between CDW and SC.

We synthesized polycrystalline samples of CeRh6Si4 and investigated its physical properties by means of magnetic susceptibility, specific heat and electrical resistivity measurements as well as LIII X-ray absorption spectroscopy. All results evidence an intermediate-valent (IV) Ce state with a valence close to 3.2 and a characteristic energy of about 300 K. Accordingly, we observe a Fermi liquid ground state at low temperatures with a slightly enhanced Sommerfeld coefficient γ = 28 mJ/molK2. Using presently available data on different compounds, we analyze the evolution of the Ce valence in the Ce-Rh-Si ternary phase diagram. The expected correlation with the distance to nearest Ce-ligands can be discerned. Thus, the evolution from a trivalent Ce3+ state in CeRh3Si2 to an IV state in CeRh6Si4 is related to a shortening of both the Ce-Rh and Ce-Si bonds in the first coordination sphere of Ce.

We synthesized polycrystalline samples of CeRh6Si4 and investigated its physical properties by means of magnetic susceptibility, specific heat and electrical resistivity measurements as well as LIII X-ray absorption spectroscopy. All results evidence an intermediate-valent (IV) Ce state with a valence close to 3.2 and a characteristic energy of about 300 K. Accordingly, we observe a Fermi liquid ground state at low temperatures with a slightly enhanced Sommerfeld coefficient γ = 28 mJ/molK2. Using presently available data on different compounds, we analyze the evolution of the Ce valence in the Ce-Rh-Si ternary phase diagram. The expected correlation with the distance to nearest Ce-ligands can be discerned. Thus, the evolution from a trivalent Ce3+ state in CeRh3Si2 to an IV state in CeRh6Si4 is related to a shortening of both the Ce-Rh and Ce-Si bonds in the first coordination sphere of Ce.

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.

We studied the magnetic, transport, and thermodynamic properties of the alloy CeTi1-xScxGe in order to shed some light into the origin of the exceptionally large antiferromagnetic (AFM) ordering temperature TN = 47 K in pure CeScGe. We observed a complex magnetic phase diagram, which present an interesting dichotomy: Despite strong changes in the nature of the ordered state, from ferromagnetic (FM) for x ≤ 0.55 to AFM for x > 0.55, the ordering temperature increases smoothly and continuously from TC = 7 K at x = 0.25 to TN = 47 K at x = 1. Within the AFM regime we observe a metamagnetic transition at a critical field increasing from H = 0 at x ≈ 0.55 to μ0 * H ≈ 6 Tesla at x = 1. Furthermore a second transition appears at TL ≤ TN for x ≥ 0.65. In contrast to observations in CeRh2Si2 or CeRh3B2, we found no evidence for a strong hybridization of the 4f electrons at large Sc contents. Therefore the exceptionally large TN of CeScGe could be attributed to the unusually strong RKKY interaction in this type of compounds.

We observed a well-defined Yb3+ electron spin resonance (ESR) line in YbPt2Sn. The single crystal ESR data show strongly anisotropic g factors, being largest in the basal plane, in agreement with magnetization data. This proves the intrinsic nature of the ESR signal. Analysis of these results indicates the crystal electric field ground state to be the Γ7 doublet. Although the Kondo and intersite interactions are at least one order of magnitude weaker than in the Kondo lattices YbRh2Si2 and YbIr2Si2, the temperature dependence of linewidth and g factors show qualitative similarities.

A Muon spin relaxation (µSR) study has been performed on the Kondo lattice heavy fermion itinerant ferromagnet CeCrGe3. Recent investigations of bulk properties have revealed a long-range ordering of Cr moments at Tc = 70 K in this compound. Our µSR investigation between 1.2 K and 125 K confirm the bulk magnetic order which is marked by a loss in initial asymmetry below 70 K accompanied with a sharp increase in the muon depolarization rate. Field dependent µSR spectra show that the internal field at the muon site is higher than 0.25 T apparently due to the ferromagnetic nature of ordering. The effect of Ti substitution on the magnetism in CeCrGe3 is presented. A systematic study has been made on polycrystalline CeCr1−xTixGe3 (0 ⩽ x ⩽ 1) using magnetic susceptibility χ(T), isothermal magnetization M(H), specific heat C(T) and electrical resistivity ρ(T) measurements which clearly reveal that the substitution of Ti for Cr in CeCrGe3 strongly influences the exchange interaction and ferromagnetic ordering of Cr moments. The Cr moment ordering temperature is suppressed gradually with increasing Ti concentration up to x = 0.50 showing Tc = 7 K beyond which Ce moment ordering starts to dominate and a crossover between Cr and Ce moment ordering is observed with a Ce moment ordering Tc = 14 K for x = 1.0. The Kondo lattice behavior is evident from temperature dependence of ρ(T) in all CeCr1−xTixGe3 samples.

The highest antiferromagnetic (AFM) temperature in Ce based compounds has been reported for CeScGe with T-N = 47 K, but its local or itinerant nature has not been deeply investigated yet. In order to shed more light into this unusually high ordering temperature we have investigated structural, magnetic, transport, and thermal properties of CeTi1-xScxGe alloys within the range of stability of the CeScSi-type structure: 0.25 <= x <= 1. Along this concentration range, this strongly anisotropic system presents a complex magnetic phase diagram with a continuous modification of its magnetic behavior, from ferromagnetism for 0.25 <= x <= 0.50 (with 7 K <= T-C <= 16 K) to AFM for 0.60 <= x <= 1 (with 19 K <= T-N <= 47 K). The onset of the AFM phase is associated to a metamagnetic transition with a critical field increasing from H-cr = 0 at x approximate to 0.55 to approximate to 6 T at x = 1, coincident with an increasing contribution of the first excited crystal electric field doublet. At a critical point x(cr) approximate to 0.65 a second transition appears at T-L <= T-N. In contrast to observations in itinerant systems like CeRh2Si2 or CeRh3B2, no evidences for significant hybridization of the 4f electrons at large Sc contents were found. Therefore, the exceptionally large T-N of CeScGe can be attributed to an increasing Ruderman-Kittel-Kasuya-Yosida interaction between Ce double layers as Sc content grows.