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Technologies that function at room temperature often require magnets with a high Curie temperature, T C , and can be improved with better materials. Discovering magnetic materials with a substantial T C is challenging because of the large number of candidates and the cost of fabricating and testing them. Using the two largest known datasets of experimental Curie temperatures, we develop machine-learning models to make rapid T C predictions solely based on the chemical composition of a material. We train a random-forest model and a k-NN one and predict on an initial dataset of over 2500 materials and then validate the model on a new dataset containing over 3000 entries. The accuracy is compared for multiple compounds' representations ("descriptors") and regression approaches. A random-forest model provides the most accurate predictions and is not improved by dimensionality reduction or by using more complex descriptors based on atomic properties. A random-forest model trained on a combination of both datasets shows that cobalt-rich and iron-rich materials have the highest Curie temperatures for all binary and ternary compounds. An analysis of the model reveals systematic error that causes the model to over-predict low- T C materials and under-predict high- T C materials. For exhaustive searches to find new high- T C materials, analysis of the learning rate suggests either that much more data is needed or that more efficient descriptors are necessary. [ABSTRACT FROM AUTHOR]

The Ce 3 − x Mg x Co 9 system evolves from a Pauli paramagnetic ground state for x = 0 to a ferromagnetic ground state for x ≈ 0.80 in single-phase, polycrystalline samples [Lamichhane, V. Taufour, A. Palasyuk, Q. Lin, S.L. Budko, and P.C. Canfield, C e 3 − x M g x C o 9 : transformation of a Pauli paramagnet into a strong permanent magnet, Phys. Rev. Appl. 9 (2018), p. 024023]. In order to better understand this behaviour, single-crystalline samples of Ce 3 − x Mg x Co 9 for x = 0.01, 0.16, 0.24, 0.35, 0.43 and 0.50 were grown using the flux growth technique, and electrical transport and magnetic properties were studied. The T C -x phase diagram we infer shows that the system has a quantum phase transition near x = 0.35, transforming to a ferromagnetic ground state. [ABSTRACT FROM AUTHOR]

Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our recent studies on the compound LaCrGe 3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change of order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point. [ABSTRACT FROM AUTHOR]

ZrMnP and HfMnP single crystals are grown by a self-flux growth technique, and structural as well as temperature dependent magnetic and transport properties are studied. Both compounds have an orthorhombic crystal structure. ZrMnP and HfMnP are ferromagnetic with Curie temperatures around 370K and 320 K, respectively. The spontaneous magnetizations of ZrMnP and HfMnP are determined to be 1.9 μB/f.u. and 2.1 μB/f.u., respectively, at 50K. The magnetocaloric effect of ZrMnP in terms of entropy change (ΔS) is estimated to be -6.7 kJ m-3 K-1 around 369K. The easy axis of magnetization is [100] for both compounds, with a small anisotropy relative to the [010] axis. At 50 K, the anisotropy field along the [001] axis is ~4.6 T for ZrMnP and ~10T for HfMnP. Such large magnetic anisotropy is remarkable considering the absence of rare-earth elements in these compounds. The first principle calculation correctly predicts the magnetization and hard axis orientation for both compounds, and predicts the experimental HfMnP anisotropy field within 25%. More importantly, our calculations suggest that the large magnetic anisotropy comes primarily from the Mn atoms, suggesting that similarly large anisotropies may be found in other 3d transition metal compounds. [ABSTRACT FROM AUTHOR]

Single crystals of Fe 5 B 2 P were grown by self-flux growth technique. Structural and electrical and magnetic anisotropic properties are studied. The Curie temperature of Fe 5 B 2 P is determined to be 655±2 K. The saturation magnetization is determined to be 1.72 μ B / Fe at 2 K. The temperature variation of the anisotropy constant K 1 is determined for the first time, reaching ∼ 0.50 MJ / m 3 at 2 K, and it is comparable to that of hard ferrites. The saturation magnetization is found to be larger than the hard ferrites. The first principle calculations of saturation magnetization and anisotropy constant are found to be consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Single crystals of Nd 4 FeOS 6 were grown from an Fe–S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd 4 MnOSe 6 -type structure ( P 6 3 mc , a =9.2693(1) Å, c =6.6650(1)Å, V =495.94(1) Å 3 , Z =2), featuring parallel chains of face-sharing [FeS 6×1/2 ] 4− trigonal antiprisms and interlinked [Nd 4 OS 3 ] 4+ cubane-like clusters. Oxygen atoms were found to be trapped by Nd 4 clusters in the [Nd 4 OS 3 ] 4 + chains. Structural differences among Nd 4 MnOSe 6 -type Nd 4 FeOS 6 and the related La 3 CuSiS 7 − and Pr 8 CoGa 3 -type structures have been described. Magnetic susceptibility measurements on Nd 4 FeOS 6 suggested the dominance of antiferromagnetic interactions at low temperature, but no magnetic ordering down to 2 K was observed. Spin-polarized electronic structure calculations revealed magnetic frustration with dominant antiferromagnetic interactions. [ABSTRACT FROM AUTHOR]

We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p* ~ 1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p* up to 7.1 GPa. The T-p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p*, a change in the behavior of the upper critical field is revealed through a scaling analysis of the slope of HC2 with the effective mass as determined from the A coefficient of the T2 term of the temperature-dependent resistivity. We show that this scaling provides a quantitative test for the changes of the superconducting gap structure and suggests the development of a kz modulation of the superconducting gap above p* as a most likely explanation. [ABSTRACT FROM AUTHOR]

To explore the possibility of quantum phase transitions and even quantum criticality in LaCrSbbased compounds, we performed measurements under pressure as well as a vanadium substitution study. The Curie temperature of LaCrSbwas found to be invariant under pressure. Although pressure was not able to suppress the ferromagnetism, chemical substitution was used as another parameter to tune the magnetism. We grew La(VCr)Sb(x= 0–1.0) single crystals and studied the series by measurements of temperature- and field-dependent magnetic susceptibility, magnetization, resistivity and specific heat. Ferromagnetism has been observed for, and the system manifests a strong anisotropy in its ordered state. The Curie temperature decreases monotonically as theVconcentration increases. For, the system enters a new magnetic state at low temperatures, and no magnetic ordering above 1.8 K can be observed for. The effective moment/Cr varies only slightly as theVconcentration increases, from 3.9for= 0 to 2.9for= 0.88. Features related to quantum criticality have not been observed in the La(VCr)Sbsystem. [ABSTRACT FROM PUBLISHER]

We report the synthesis of hexagonal LaVxCr1-xGe3 (x = 0-0.21,1.00) single crystals and present a systematic study of this series by measurements of temperature- and field-dependent magnetic susceptibility, magnetization, resistivity, and specific heat. Ferromagnetism has been observed for x = 0-0.21. The Curie temperature declines monotonically as the V concentration increases. Single-crystalline samples could only be grown for x values up to 0.21 for which the transition temperature was suppressed down to 36 K. Although we could not fully suppress Tc via V substitution, for x = 0.16, we performed magnetization measurements under pressure. The ferromagnetic state is suppressed under pressure at an initial rate of dTc/dp ≃ -11.7 K/GPa and. vanishes by 3.3 GPa. The increase of the Rhodes-Wohlfarth ratio suggests that the ferromagnetism in this system evolves toward itinerant as the V concentration increases. [ABSTRACT FROM AUTHOR]

We report the temperature-pressure-magnetic-field phase diagram of the ferromagnetic Kondo-lattice CeTiGe3 determined by means of electrical resistivity measurements. Measurements up to ~ 5.8 GPa reveal a rich phase diagram with multiple phase transitions. At ambient pressure, CeTiGe3 orders ferromagnetically at TC = 14 K. Application of pressure suppresses TC, but a pressure-induced ferromagnetic quantum criticality is avoided by the appearance of two new successive transitions for p > 4.1 GPa that are probably antiferromagnetic in nature. These two transitions are suppressed under pressure, with the lower-temperature phase being fully suppressed above 5.3 GPa. The critical pressures for the presumed quantum phase transitions are p1 ≅ 4.1 GPa and p2 ≅ 5.3 GPa. Above 4.1 GPa, application of magnetic field shows a tricritical point evolving into a wing-structure phase with a quantum tricritical point at 2.8 T at 5.4 GPa, where the first-order antiferromagnetic-ferromagnetic transition changes into the second-order antiferromagnetic-ferromagnetic transition. [ABSTRACT FROM AUTHOR]

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0(5) GPa for temperatures below 150 K. Density functional theory calculations also find a sudden transition to a collapsed tetragonal state near 4 GPa, as As-As bonding develops across the Ca layer. Bonding across the K layer only occurs for p≥12 GPa. These findings demonstrate a different type of collapsed tetragonal phase in CaKFe4As4 as compared to CaFe2As2: a half-collapsed tetragonal phase. [ABSTRACT FROM AUTHOR]

We study the evolution of the Kondo effect in heavy fermion compounds, Yb(Fe1-xCox)2Zn20 (0 ≤ x ≤ 1), by means of temperature-dependent electric resistivity and specific heat. The ground state of YbFe2Zn20 can be well described by a Kondo model with degeneracy N = 8 and a TK ~ 30 K. The ground state of YbCo2Zn20 is close to a Kondo state with degeneracy N = 2 and a much lower TK ~ 2 K, even though the total crystalline electric field (CEF) splittings are similar for YbFe2Zn20 and YbCo2Zn20. Upon Co substitution, the coherence temperature of YbFe2Zn20 is suppressed, accompanied by an emerging Schottky-like feature in specific heat associated with the thermal depopulation of CEF levels upon cooling. For 0.4 ≲ x ≲ 0.9, the ground state remains roughly the same, which can be qualitatively understood by Kondo effect in the presence of CEF splitting. There is no clear indication of Kondo coherence in resistivity data down to 500 mK within this substitution range. The coherence reappears at around x ≳ 0.9 and the coherence temperature increases with higher Co concentration levels. [ABSTRACT FROM AUTHOR]

This paper presents details of Mg-assisted flux growth of Sm2Co17 single crystals in a Ta crucible well below the melting temperature of binary Sm2Co17. Both the crushed single crystalline powder x-ray diffraction (XRD) and single crystalline XRD data revealed the Th2Zn17 type rhombohedral(R-3m) crystal structure. Ta atom is found to be statistically replacing the Co-Co dumbbell with its position being at the center of the dumbbell. The Curie temperature of our lightly Mg and Ta doped Sm2Co17 sample is determined to be ∼1100 K using method of generalized Bloch law fitting of easy axis spontaneous magnetization data. [ABSTRACT FROM AUTHOR]

We consider the phase diagram of a ferromagnetic system driven to a quantum phase transition with a tuning parameter p. Before being suppressed, the transition becomes of the first order at a tricritical point, from which wings emerge under application of the magnetic field H in the T-p-H phase diagram. We show that the edge of the wings merge with tangent slopes at the tricritical point. [ABSTRACT FROM AUTHOR]

The temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets. [ABSTRACT FROM AUTHOR]

We study magnetic domains in Nd2Fe14B single crystals using high resolution magnetic force microscopy (MFM). Previous MFM studies and small angle neutron scattering experiments suggested the presence of nanoscale domains in addition to optically detected micrometer-scale ones. We find, in addition to the elongated, wavy nanodomains reported by a previous MFM study, that the micrometer-sized, star-shaped fractal pattern is constructed of an elongated network of nanodomains ∼20 nm in width, with resolution-limited domain walls thinner than 2 nm. While the microscopic domains exhibit significant resilience to an external magnetic field, some of the nanodomains are sensitive to the magnetic field of the MFM tip. [ABSTRACT FROM AUTHOR]

The pressure dependence of the upper critical field, Hc2,c, of single crystalline FeSe was studied using measurements of the interplane resistivity, pc, in magnetic fields parallel to tetragonal c axis. Hc2,c(T) curves obtained under hydrostatic pressures up to 1.56 GPa, the range over which the superconducting transition temperature, Tc, of FeSe exhibits a nonmonotonic dependence with local maximum at p1≈?0.8 GPa and local minimum at p2?≈1.2 GPa. The slope of the upper critical field at Tc,(dHc2,c/dT)Tc, also exhibits a nonmonotonic pressure dependence with distinct changes at p1 and p2. For pp2 the slope is in good semiquantitative agreement with a single band, orbital Helfand-Werthamer theory with Fermi velocities determined from Shubnikov-de Haas measurements. This finding indicates that Fermi surface changes are responsible for the local minimum of Tc(p) at p2?≈1.2 GPa. [ABSTRACT FROM AUTHOR]

Single crystals of Nd4FeOS6 are grown from an Fe-S eutectic solution using a mixture of the elements in the molar ratio of Nd:Fe:S = 4:55:41 (alumina crucible, heating to 1150 °C over 12 h; cooling to 1000 °C with a rate of 1 °C/h). [ABSTRACT FROM AUTHOR]

Small-angle neutron scattering has been used to study the vortex lattice in superconducting MgB2 doped with either manganese or carbon to achieve a similar suppression of the critical temperature. Measurements were performed with the magnetic field applied along the c axis, where the vortex lattice in pure MgB2 is known to undergo a field- and temperature-driven 30° rotation transition. For Mn doping, the vortex lattice phase diagram remains qualitatively similar to that of pure MgB2, indicating only a modest effect on the vortex-- vortex interaction. In contrast, the vortex lattice rotation transition is completely suppressed in the C-doped case, probably due to a change in the electronic structure which affects the two-band/two-gap nature of superconductivity in MgB2. The vortex lattice longitudinal correlation length shows the opposite behavior, remaining roughly unchanged between pure and C-doped MgB2 while it is significantly reduced in the Mn-doped case. However, the extensive vortex lattice metastability and related activated behavior, observed in conjunction with the vortex lattice transition in pure MgB2, are also seen in the Mn-doped sample. This shows that the vortex lattice disordering is not associated with a substantially increased vortex pinning. [ABSTRACT FROM AUTHOR]

We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB2. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both a bands follows a BCS-like variation with temperature with Δ0 ∼ 7 meV. The value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We also observe in-gap states confined to kF of the σ band that occur at some locations of the sample surface. The energy of this excitation, ∼3 meV, is somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin. [ABSTRACT FROM AUTHOR]

We use a tunable laser angle-resolved photoemission spectroscopy to study the electronic properties of the prototypical multiband BCS superconductor MgB2. Our data reveal a strong renormalization of the dispersion (kink) at ∼65 meV, which is caused by the coupling of electrons to the E2g phonon mode. In contrast to cuprates, the 65 meV kink in MgB2 does not change significantly across Tc. More interestingly, we observe strong coupling to a second, lower energy collective mode at a binding energy of 10 meV. This excitation vanishes above Tc and is likely a signature of the elusive Leggett mode. [ABSTRACT FROM AUTHOR]

The well-known BaAl4-type structure consists of three ordered ternary derivatives, i.e., BaNiSn3- ( I4 mm), ThCr2Si2- ( I4/ mmm), and CaBe2Ge2-type ( P4/ nmm). Few systems, such as Ba-Au-Sn, have been confirmed to manifest all three types as a function of valence electron count. In this work, the SrAu xSn4- x solid solution at the 600 °C section was studied thoroughly using both single crystal and powder X-ray diffraction. The crystal structures and phase width for the CaBe2Ge2-type SrAu xSn4- x solid solution were established to be a = 4.6528(2)-4.6233(3) Å and c = 11.3753(4)-11.2945(10) Å for x ≈ 1.65(1)-2.19(1). In the structure of SrAu2Sn2, no Au/Sn mixing was found, but for x < 2 compositions, Au/Sn mixings were only located at the Wyckoff 2 a (¾ ¼ 0) site and for x > 2 compositions, at the 2 b (¾ ¼ ½) site. Differential scanning calorimetry (DSC) analyses indicated that no phase transition occurred for the CaBe2Ge2-type SrAu xSn4- x phase up to 950 °C. Attempts to synthesize the ThCr2Si2- and BaNiSn3-type SrAu xSn4- x phases under the same reaction conditions were unsuccessful, and the BaNiSn3-type phase could not be attained even at a pressure of 3 GPa. The instability of a BaNiSn3-type 'SrAuSn3' was investigated by both DSC measurements and first principles electronic structure calculations. [ABSTRACT FROM AUTHOR]

Abstract: Single crystals of RCo2Ge2 (R=Y, La–Nd, Sm–Tm) were grown using a self-flux method and were characterized by room-temperature powder X-ray diffraction; anisotropic, temperature and field dependent magnetization; temperature and field dependent, in-plane resistivity; and specific heat measurements. In this series, the majority of the moment-bearing members order antiferromagnetically; YCo2Ge2 and LaCo2Ge2 are non-moment-bearing. Ce is trivalent in CeCo2Ge2 at high temperatures, and exhibits an enhanced electronic specific heat coefficient due to the Kondo effect at low temperatures. In addition, CeCo2Ge2 shows two low-temperature anomalies in temperature-dependent magnetization and specific heat measurements. Three members (R=Tb–Ho) have multiple phase transitions above 1.8K. Eu appears to be divalent with total angular momentum L=0. Both EuCo2Ge2 and GdCo2Ge2 manifest essentially isotropic paramagnetic properties consistent with J=S=7/2. Clear magnetic anisotropy for rare-earth members with finite L was observed, with ErCo2Ge2 and TmCo2Ge2 manifesting planar anisotropy and the rest members manifesting axial anisotropy. The experimentally estimated crystal electric field (CEF) parameters B 2 0 were calculated from the anisotropic paramagnetic θ ab and θ c values and follow a trend that agrees well with theoretical predictions. The ordering temperatures, , as well as the polycrystalline averaged paramagnetic Curie–Weiss temperature, Θ avg , for the heavy rare-earth members deviate from the de Gennes scaling, as the magnitude of both is the highest for Tb, which is sometimes seen for extremely axial systems. Except for SmCo2Ge2, metamagnetic transitions were observed at 1.8K for all members that ordered antiferromagnetically. [Copyright &y& Elsevier]

Alumina is an essential ceramic insulator, while carbon nanotubes (CNTs) have intriguing mechanical, thermal, electrical, and magnetic properties. We report on the synthesis of CNTs/Al 2 O 3 nanocomposites using the chemical vapor deposition (CVD) process using iron as a catalyst. The as-prepared composite's structure and morphology are characterized by transmission electron microscope, scanning electron microscope, X-ray diffractometer, thermogravimetric analyzer, and Mössbauer spectroscopy. The experimental results show that these composites contain CNTs of an average diameter of 40 nm distributed homogenously within the alumina matrix. The percentage of CNTs within the composites is at 7%. The CNT/Al 2 O 3 nanocomposites demonstrate a dramatic enhancement of ferromagnetic properties during vibrating sample magnetization measurements. As compared to the magnetization of 0.03 e.m.u./g at an applied field of 1.5 T for the Fe-catalyzed Al 2 O 3 , the saturation magnetization of CNT/Al 2 O 3 is 1.78 e.m.u./g, which represents an increment of ∼5800%. The coercivity of CNTs/Al 2 O 3 composites increased from 0.036 T at 300 K to 0.285 T at 5 K. This study provides a relatively simple approach to blending the magnetic properties with potential thermoelectric materials. • Carbon nanotube/alumina nanocomposites synthesized by one-step chemical vapor deposition process. • The saturation magnetization of the composites represents ~5800% increment as compared to the starting material. • The composites demonstrated significant magnetic "hardening" under cryogenic conditions due to frozen magnetic moments. [ABSTRACT FROM AUTHOR]

Unconventional superconductors have Cooper pairs with lower symmetries than in conventional superconductors. In most unconventional superconductors, the additional symmetry breaking occurs in relation to typical ingredients such as strongly correlated Fermi liquid phases, magnetic fluctuations, or strong spin-orbit coupling in noncentrosymmetric structures. In this article, we show that the time-reversal symmetry breaking in the superconductor LaNiGa2 is enabled by its previously unknown topological electronic band structure, with Dirac lines and a Dirac loop at the Fermi level. Two symmetry related Dirac points even remain degenerate under spin-orbit coupling. These unique topological features enable an unconventional superconducting gap in which time-reversal symmetry can be broken in the absence of other typical ingredients. Our findings provide a route to identify a new type of unconventional superconductors based on nonsymmorphic symmetries and will enable future discoveries of topological crystalline superconductors. Topological superconducting systems are expected to exhibit a range of exotic physics which are particularly useful for application in quantum computing technologies. Here, the authors report the synthesis of LaNiGa2 which exhibits both topological and superconducting features originating from its nonsymmorphic crystal structure. [ABSTRACT FROM AUTHOR]

Magnetic carbon nanotubes (CNTs)/alumina (Al2O3) nanocomposites were synthesized by the direct growth of CNTs on alumina by chemical vapor deposition (CVD) process. X-ray diffraction studies show that the crystalline structure of alumina nanoparticles remains preserved during the CVD process. Electron microscopy studies reveal the uniform distribution of CNTs within the alumina matrix. CNTs of average diameter 20 nm are spread around alumina particles of size 120 nm. The proportion of CNTs in alumina composites is determined to be approximately 10% from the thermogravimetric analysis. CNT-reinforced alumina nanocomposites demonstrate a significant improvement of the magnetic properties as compared with pristine alumina powder. The diamagnetic property of alumina nanopowder is transformed into a strongly pronounced ferromagnetic response upon the incorporation of CNTs. The saturation magnetization increased by ~ 2500%, and a pronounced coercivity of 68 Oe was observed in the nanocomposites. It is suggested that the encapsulation of cobalt inside the CNTs constrains the magnetic moments to result in higher saturation magnetization. Hence, the CNTs/Al2O3 system synthesized in this work can be employed to engineer novel ceramic composites with enhanced magnetic properties. [ABSTRACT FROM AUTHOR]

We report the growth, structure and characterization of BaZnGa, identifying it as the sole known ternary compound in the Ba–Zn–Ga system. Single crystals of BaZnGa can be grown out of excess Ba–Zn and adopt a tI36 structure type. There are three unique Ba sites and three M = Zn/Ga sites. Using DFT calculations we can argue that whereas one of these three M sites is probably solely occupied by Ga, the other two M sites, most likely, have mixed Zn/Ga occupancy. Temperature-dependent resistivity and magnetization measurements suggest that BaZnGa is a poor metal with no electronic or magnetic phase transitions between 1.8 and 300 K. [ABSTRACT FROM PUBLISHER]

Planar hydrocarbon-like metal clusters may foster new insights linking organic molecules with conjugated π-π bonding interactions and inorganic structures in terms of their bonding characteristics. However, such clusters are uncommon in polar intermetallics. Herein, we report two polar intermetallic phases, Pr5Co2Ge3 and Pr7Co2Ge4, both of which feature such planar metal clusters, namely, ethylene-like [Co2Ge4] clusters plus the concatenated forms and polyacene-like [Co2Ge2] n ribbons in Pr5Co2Ge3, and 1,2,4,5-tetramethylbenzene-like [Co4Ge6] cluster in Pr7Co2Ge4. Just as in the related planar organic structures, these metal-metalloid species are dominated by covalent bonding interactions. Both compounds magnetically order at low temperature with net ferromagnetic components: Pr5Co2Ge3 through a series of transitions below 150 K and Pr7Co2Ge4 through a single ferromagnetic transition at 19 K. Spin-polarized electronic structure calculations for Pr7Co2Ge4 reveal strong spin-orbit coupling within Pr and considerable magnetic contributions from Co atoms. This work suggests that similar structural chemistry can emerge for other rare-earth/late-transition-metal/main-group systems. [ABSTRACT FROM AUTHOR]

We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the s band, which is caused by electron coupling to the E2g phonon mode, is shifted to higher binding energy by ~3.5 meV in Mg10B2 and the shift is not affected by superconducting transition. These results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown. [ABSTRACT FROM AUTHOR]

Single crystals of Bi2Rh3S2 and Bi2Rh3.5S2 were synthesized by solution growth, and the crystal structures and thermodynamic and transport properties of both compounds were studied. In the case of Bi2Rh3S2, a structural first-order transition at around 165 K is identified by single-crystal diffraction experiments, with clear signatures visible in resistivity, magnetization, and specific heat data. No superconducting transition for Bi2Rh3S2 was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi2Rh3.5S2; however, bulk superconductivity with a critical temperature, Tc≈1.7 K, was observed. The Sommerfeld coefficient Υ and the Debye temperature (ΘD) were found to be 9.41 mJ mol-1K-2 and 209 K, respectively, for Bi2Rh3S2, and 22 mJ mol-1K-2 and 196 K, respectively, for Bi2Rh3.5S2. Study of the specific heat in the superconducting state of Bi2Rh3.5S2 suggests that Bi2Rh3.5S2 is a weakly coupled, BCS superconductor. [ABSTRACT FROM AUTHOR]

Low-temperature measurements of the magnetocrystalline anisotropy energy K in (Fe1-xCox)2B alloys are reported, and the origin of this anisotropy is elucidated using a first-principles electronic structure analysis. The calculated concentration dependence K(x) with a maximum near x = 0.3 and a minimum near x = 0.8 is in excellent agreement with experiment. This dependence is traced down to spin-orbital selection rules and the filling of electronic bands with increasing electronic concentration. At the optimal Co concentration, K depends strongly on the tetragonality and doubles under a modest 3% increase of the c/a ratio, suggesting that the magnetocrystalline anisotropy can be further enhanced using epitaxial or chemical strain. [ABSTRACT FROM AUTHOR]

The aim of this study is to compare the magnetic behavior of URu2Si2 under uniaxial stress along the a axis with the behavior under hydrostatic pressure. Both are very similar, but uniaxial stress presents a critical stress Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed [0.33(5) GPa] that is smaller than the hydrostatic critical pressure px (0.5 GPa) where the ground state switches from a HO (hidden-order) to AF (antiferromagnetic) ground state. From these critical values and Larmor neutron diffraction, we conclude that the magnetic properties are governed by the shortest U-U distance in the plane (a lattice parameter). Under stress, the orthorhombic unit cell stays centered. A key point shown by this study is the presence of a threshold for the uniaxial stress along the a axis before the appearance of the large AF moment, which indicates no mixture of the order parameter between the HO ground state and the AF one as under hydrostatic pressure. The two most intense longitudinal magnetic excitations at Q0 = (1,0,0) and Q1 = (0.6,0,0) were measured in the HO state: the excitation at Q0 decreases in energy while the excitation at Q1 increases in energy with the uniaxial stress along the a axis. The decrease of the energy of the excitation at Q0 seems to indicate a critical energy-gap value of 1.2(1) meV at Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. A similar value was derived from studies under hydrostatic pressure at px. [ABSTRACT FROM AUTHOR]

Abstract: Thanks to the discovery in the last decade of three uranium ferromagnetic superconductors, UGe2, URhGe and UCoGe, the fascinating aspects of the interplay between the triplet state of Cooper pairing and ferromagnetism have emerged. Furthermore, as the ferromagnetic properties in the normal state are quite different with respect to the proximity of the ferromagnetic–paramagnetic instabilities, the feedback with the coexistence of superconductivity gives rise to quite different boundaries in pressure and magnetic field. Special attention is given on the location of the materials with respect to the tricriticality and on the reinforcement of SC in a transverse field response with respect to the direction of the FM sublattice magnetization. The other facts of the interplay between FM and SC is briefly mentioned. [Copyright &y& Elsevier]

● Crystal Structure, magnetic and resistivity measurements of (Ce 0.85 Ti 0.15)Ge 3 O 0.5. ● Ti substitutions and interstitial O stabilize the CeGe 3 compound at ambient pressure. ● Study of stability of the compounds in RTr 3 system. Sub-oxides with the anti-perovskite structure constitute a large part of the interstitial stabilized compounds with novel chemical and physical properties, especially in the systems containing rare earth elements and/or early transition metal elements. A new sub-oxide compound, (Ce 0.85 Ti 0.15)Ge 3 O 0.5 , is synthesized by flux growth. The compound crystallizes in a cubic structure which can be considered as an ordered vacancy variant of anti-perovskite-structure or an ordered interstitial variant of the Cu 3 Au type, with a space group of Fm -3 m (225). The structure is refined from X-ray single crystal methods. The compound may be considered as a compound stabilized by chemical pressure generated by the substitution and the interstitials atoms. The stability of the compounds in RTr 3 systems (R = rare earth elements except Pm and Sc, Tr = tetrel elements such as Si, Ge, Sn, Pb) seem to be highly correlated to the ratio of the rare earth elements' radii to the main group elements' atomic radii. The magnetic property of the compound confirms the 4+ valence of the Ce atoms. The resistivity measurement of the compound shows that it is metallic. [ABSTRACT FROM AUTHOR]

• The Callen-and-Callen model cannot explain the temperature dependence of the anisotropy constant. • A realistic electronic structure analysis with disordered moments approach is given. • It successfully accounts for the temperature and concentration dependence of the anisotropy. • Melt-spinning experiment indicates that this system shows rapid crystallization. New determination of the magnetic anisotropy from single crystals of (Fe 1 - x Co x) 2 B alloys are presented. The anomalous temperature dependence of the anisotropy constant is discussed using the standard Callen-Callen theory, which is shown to be insufficient to explain the experimental results. A more material specific study using first-principles calculations with disordered moments approach gives a much more consistent interpretation of the experimental data. Since the intrinsic properties of the alloys with x = 0.3 - 0.35 are promising for permanent magnets applications, initial investigation of the extrinsic properties are described, in particular the crystallization of melt spun ribbons with Cu, Al, and Ti additions. Previous attempts at developing a significant hysteresis have been unsuccessful in this system. Our melt-spinning experiment indicates that this system shows rapid crystallization. [ABSTRACT FROM AUTHOR]

A self-consistent two-gap γ -model is used to quantitatively describe several thermodynamic properties of MgB 2 superconductor. The superconducting coupling matrix, ν i j , was obtained from the fitting of the superfluid density in the entire superconducting temperature range. Using this input, temperature-dependent superconducting gaps, specific heat, and upper critical fields were calculated with no adjustable parameters and compared with the experimental data as well as with the first-principles calculations. The observed agreement between fit and data shows that γ -model provides adequate quantitative description of the two-gap superconductivity in MgB 2 and may serve as a relatively simple and versatile self-consistent description of the thermodynamic quantities in multi-gap superconductors. [ABSTRACT FROM AUTHOR]

The pressure dependence of the structural, magnetic, and superconducting transitions and of the superconducting upper critical field were studied in sulfur-substituted Fe(Se1-xSx). Resistance measurements were performed on single crystals with three substitution levels (x = 0.043, 0.096, 0.12) under hydrostatic pressures up to 1.8 GPa and in magnetic fields up to 9 T and were compared to data on pure FeSe. Our results illustrate the effects of chemical and physical pressure on Fe (Se1-xSx). On increasing sulfur content, magnetic order in the low-pressure range is strongly suppressed to a small domelike region in the phase diagrams. However, Ts is much less suppressed by sulfur substitution, and Tc of Fe(Se1-xSx) exhibits similar nonmonotonic pressure dependence with a local maximum and a local minimum present in the low-pressure range for all x. The local maximum in T c coincides with the emergence of the magnetic order above Tc. At this pressure the slope of the upper critical field decreases abruptly, which may indicate a Fermi-surface reconstruction. The minimum of Tc correlates with a broad maximum of the upper critical field slope normalized by Tc. [ABSTRACT FROM AUTHOR]

Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below TN=255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to TN=236 K at 5.22 GPa. The pressure dependencies of (i) TN, (ii) the residual resistivity ratio, and (iii) the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. For pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states. [ABSTRACT FROM AUTHOR]

The synthesis and crystallographic, thermodynamic, and transport properties of single crystalline Rh9In4S4 were studied. The resistivity, magnetization, and specific heat measurements all clearly indicate bulk superconductivity with a critical temperature, Tc∼2.25 K. The Sommerfeld coefficient γ and the Debye temperature (ΘD) were found to be 34 mJ mol-1 K-2 and 217 K, respectively. The observed specific heat jump, ΔC/γTc=1.66, is larger than the expected BCS weak coupling value of 1.43. Ginzburg-Landau (GL) ratio of the low-temperature GL-penetration depth, λGL≈5750 Å, to the GL-coherence length, ξGL≈94 Å, is large: κ ∼60. Furthermore, we observed a peak effect in the resistivity measurement as a function of both temperature and magnetic field. [ABSTRACT FROM AUTHOR]