Single crystal growth from light, volatile, and reactive materials using lithium and calcium flux

We present a method for the solution growth of single crystals from reactive Li and Ca melts and its application to the synthesis of several, representative compounds. Among these, single crystalline Li3N, Li2(Li{1-x}Tx)N with T = {Mn, Fe, Co}, LiCaN, Li2C2, LiRh, and LiIr from Li-rich flux as well as Ca2N, CaNi2, CaNi3, YbNi2, Y2Ni7, and LaNi5 from Ca-rich flux could be obtained. Special emphasize is given on the growth of nitrides using commercially available Li3N and Ca3N2 powders as the nitrogen source instead of N2 gas.Comment: 40 pages, 20 figures, reference list update

Preserved entropy and fragile magnetism

A large swath of strongly correlated electron systems can be associated with the phenomena of preserved entropy and fragile magnetism. In this overview we present our thoughts and plans for the discovery and development of lanthanide and transition metal based, strongly correlated systems that are revealed by suppressed, fragile magnetism or grow out of preserved entropy. We will present and discuss current examples such as YbBiPt, YbAgGe, YbFe2Zn20, PrAg2In, BaFe2As2, CaFe2As2, LaCrSb3 and LaCrGe3 as part of our motivation and to provide illustrative examples

Frequency dependence of the spin glass freezing temperatures in icosahedral R - Mg - Zn (R = rare earth) quasicrystals

We present ac susceptibility measurements with the frequency spanning three orders of magnitude on single grain, icosahedral R - Mg - Zn (R = rare earth) quasicrystals. The freezing temperature in Gd-based, Heisenberg spin glasses in this family increases by ~ 2% with a frequency increase from 10 Hz to 10 kHz, whereas the freezing temperature in the non-Heisenberg members of the family is significantly more responsive to the frequency change (by 16 - 22 %), suggesting that an additional magnetic anisotropy distribution in the non-Heisenberg spin glasses causes changes in the low frequency magnetic dynamics

Specific heat jump at the superconducting transition temperature in Ba(Fe(1-x)Cox)2As2 and Ba(Fe(1-x)Nix)2As2 single crystals

We present detailed heat capacity measurements for Ba(Fe(1-x)Cox)2As2 and Ba(Fe(1-x)Nix)2As2 single crystals in the vicinity of the superconducting transitions. The specific heat jump at the superconducting transition temperature (Tc), Delta Cp/Tc, changes by a factor ~ 10 across these series. The Delta Cp/T$ vs. Tc data of this work (together with the literature data for Ba(Fe0.939Co0.061)2As2, (Ba0.55K0.45)Fe2As2, and (Ba0.6K0.4)Fe2As2) scale well to a single log-log plot over two orders of magnitude in Delta Cp/Tc and over about an order of magnitude in Tc, giving Delta Cp/Tc ~ Tc^2

Single crystal growth and characterization of the large-unit-cell compound Cu13Ba

Single crystals of Cu$_{13}$Ba were successfully grown out of Ba-Cu self flux. Temperature dependent magnetization, $M(T)$, electrical resistivity, $\rho(T)$, and specific heat, $C_p(T)$, data are reported. Isothermal magnetization measurements, $M(H)$, show clear de Haas-van Alphen oscillations at $T$ = 2 K for applied fields as low as $\mu_0H$ = 1T. An anomalous behavior of the magnetic susceptibility is observed up to $T$ ~ 50K reflecting the effect of de Haas-van Alphen oscillations at fairly high temperatures. The field- and temperature-dependencies of the magnetization indicate the presence of diluted magnetic impurities with a concentration of the order of 0.01at.%. Accordingly, the minimum and lower temperature rise observed in the electrical resistivity at and below $T$ = 15K is attributed to the Kondo impurity effect.Comment: 6 pages, 8 figures, accepted for publication in J. Alloys Comp

Thermal expansion of CaFe2As2: effect of cobalt doping and post-growth thermal treatment

We report thermal expansion measurements on Ca(Fe_(1-x)Co_x)_2As_2 single crystals with different thermal treatment, with samples chosen to represent four different ground states observed in this family. For all samples thermal expansion is anisotropic with different signs of the in-plane and c-axis thermal expansion coefficients in the high temperature, tetragonal phase. The features in thermal expansion associated with the phase transitions are of opposite signs as well, pointing to a different response of transition temperatures to the in-plane and the c-axis stress. These features, and consequently the inferred pressure derivatives, are very large, clearly and substantially exceeding those in the Ba(Fe_(1-x)Co_x)_2As_2 family. For all transitions the c-axis response is dominant

Anisotropic magnetization and resistivity of single crystalline RNi1-xBi2+-y (R = La-Nd, Sm, Gd-Dy)

We present a detailed study of RNi1-xBi2+-y (R = La-Nd, Sm, Gd-Dy) single crystals by measurements of stoichiometry and temperature dependent magnetic susceptibility, magnetization, and electrical resistivity. This series forms with partial Ni occupancy as well as a variable Bi occupancy. For R = Ce-Nd, Sm, Gd-Dy, the RNi1-xBi2+-y compounds show local-moment like behavior and order antiferromagnetically at low temperatures. Determination of anisotropies as well as antiferromagnetic ordering temperatures for RNi1-xBi2+-y (R = Ce-Nd, Sm, Gd-Dy) have been made. Although crystalline samples from this family exhibit minority, second phase superconductivity at low temperatures associated with Ni-Bi and Bi contamination, no evidence of bulk superconductivity has been observed

Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on physical properties of CaFe2_{2}As2_{2}

We performed systematic studies of the combined effects of annealing/quenching temperature ({\itshape T}$_{A/Q}$) and T = Ni, Rh substitution ({\itshape x}) on the physical properties of Ca(Fe$_{1-x}$T$_{x}$)$_{2}$As$_{2}$. We constructed two-dimensional, {\itshape T}$_{A/Q}$-{\itshape x} phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co-substitution. Ni-substitution, which brings one more extra electron per substituted atom and suppresses the {\itshape c}-lattice parameter at roughly the same rate as Co-substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic in the {\itshape T}$_{A/Q}$-{\itshape x} space as that found for Co-substitution, but has the parameter range for superconductivity shrunk (roughly by a factor of two). This result is similar to what is found when Co- and Ni-substituted BaFe$_{2}$As$_{2}$ are compared. On the other hand, Rh-substitution, which brings the same amount of extra electrons as does Co-substitution, but suppresses the {\itshape c}-lattice parameter more rapidly, has a different phase diagram. The collapsed tetragonal phase exists much more pervasively, to the exclusion of the normal, paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic phase space is noticeably reduced, and the superconducting region is substantially suppressed, essentially truncated by the collapsed tetragonal phase. In addition, we found that whereas for Co-substitution there was no difference between phase diagrams for samples annealed for one or seven days, for Ni- and Rh- substitutions a second, reversible, effect of annealing was revealed by seven-day anneals

Physical properties of V1−x_{1-x}Tix_{x}O2_{2} (0 << x << 0.187) single crystals

Free standing, low strain, single crystals of pure and titanium doped VO$_{2}$ were grown out of an excess of V$_{2}$O$_{5}$ using high temperature solution growth techniques. At $T_{MI} \sim$ 340 K, pure VO$_{2}$ exhibits a clear first-order phase transition from a high-temperature paramagnetic tetragonal phase (R) to a low-temperature non-magnetic monoclinic phase (M1). With Ti doping, another monoclinic phase (M2) emerges between the R and M1 phases. The phase transition temperature between R and M2 increases with increasing Ti doping while the transition temperature between M2 and M1 decreases.Comment: 11 pages, 8 figure

Non-conventional superconducting fluctuations in Ba(Fe1-xRhx)2As2 iron-based superconductors

We measured the static uniform spin susceptibility of Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron-based superconductors, over a broad range of doping ($0.041\leq x\leq 0.094$) and magnetic fields. At small fields ($H \le$ 1 kOe) we observed, above the transition temperature $T_c$, the occurrence of precursor diamagnetism, which is not ascribable to the Ginzburg-Landau theory. On the contrary, our data fit a phase fluctuation model, which has been used to interpret a similar phenomenology occurring in the high-$T_c$ cuprate superconductors. On the other hand, in presence of strong fields the unconventional fluctuating diamagnetism is suppressed, whereas 3D fluctuations are found, in agreement with literature