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Experimental and theoretical studies on superconductivity in ${\mathrm{SrIr}}_{2}$ and ${\mathrm{SrRh}}_{2}$ Laves phases are presented. The measured resistivity, heat capacity, and magnetic susceptibility confirm the superconductivity of these compounds with ${T}_{c}=6.07$ and 5.41 K, respectively. Electronic structure calculations show that the Fermi surface is mostly contributed by $5d$ ($4d$) electrons of Ir (Rh), with Sr atoms playing the role of electron donors. The effect of the spin-orbit coupling is analyzed and found to be important in both materials. Lattice dynamics and electron-phonon coupling (EPC) are studied and the strong electron-phonon interaction is found, contributed mostly by the low-frequency Ir and Rh vibrations. The enhancement of EPC, when compared to weakly coupled metallic Ir and Rh, is explained by the strong modifications in the propagation of phonons in the network of Ir (Rh) tetrahedrons, which are the building blocks of the Laves phase, and originate from the metallic fcc structures of elemental iridium and rhodium.

A polycrystalline sample of superconducting $\mathrm{ThI}{\mathrm{r}}_{3}$ was obtained by arc-melting Th and Ir metals. Powder x-ray diffraction revealed that the compound crystalizes in a rhombohedral crystal structure (R-3m, s.g. #166) with the lattice parameters: $a=5.3394(1)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=26.4228(8)\phantom{\rule{0.16em}{0ex}}\AA{}$. Normal and superconducting states were studied by magnetic susceptibility, electrical resistivity, and heat capacity measurements. The results showed that $\mathrm{ThI}{\mathrm{r}}_{3}$ is a type-II superconductor (Ginzburg-Landau parameter $\ensuremath{\kappa}=38)$ with the critical temperature ${T}_{\mathrm{c}}=4.41\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The heat capacity data yielded the Sommerfeld coefficient $\ensuremath{\gamma}=17.6\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/(\mathrm{mo}\mathrm{l}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{2})$ and the Debye temperature ${\mathrm{\ensuremath{\Theta}}}_{\mathrm{D}}=169\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The ratio $\mathrm{\ensuremath{\Delta}}C/(\ensuremath{\gamma}{T}_{\mathrm{c}})=1.6$, where $\mathrm{\ensuremath{\Delta}}C$ stands for the specific heat jump at ${T}_{\mathrm{c}}$, and the electron--phonon coupling constant ${\ensuremath{\lambda}}_{e\ensuremath{-}p}=0.74$ suggest that $\mathrm{ThI}{\mathrm{r}}_{3}$ is a moderate-strength superconductor. The experimental studies were supplemented by band structure calculations, which indicated that the superconductivity in $\mathrm{ThI}{\mathrm{r}}_{3}$ is governed mainly by $5d$ states of iridium. The significantly smaller band-structure value of Sommerfeld coefficient as well as the experimentally observed quadratic temperature dependence of resistivity and enhanced magnetic susceptibility suggest the presence of electronic interactions in the system, which compete with superconductivity.

Detailed studies of specific heat, magnetization, and magnetic torque of a single crystal of ${\mathrm{LiNiPO}}_{4}$ olivine are presented. Olivines attract attention as promising for application as cathodes in Li-ion batteries and exhibiting a unique set of properties. ${\mathrm{LiNiPO}}_{4}$ is the unique olivine, in which antiferromagnetic order develops in two steps, i.e., at 21.8 K, the second-order transition to an incommensurate phase and then, at 20.9 K, the first-order transition to a commensurate phase appears. Specific heat studies, supplemented by the ``slope analysis procedure,'' revealed a splitting of the specific heat anomaly accompanying the first-order transition, which suggests that actually, these are two coupled transitions, one of which can be the ferroelectric one. The specific heat was measured as a function of temperature for a series of fixed external magnetic field $B$ values. As the result, analytical equations describing the phase transition lines in the $T\text{\ensuremath{-}}B$ plane were determined and evolution of a shape of the specific heat anomalies accompanying the phase transitions, observed in the powder sample under influence of $B$, was modeled. Angular dependence of magnetic torque and of magnetization for $B$ rotating within the $a\text{\ensuremath{-}}c$ and $b\text{\ensuremath{-}}c$ crystalline planes was measured for several fixed temperature and $B$ values. Based on these results, we found a new effect, that we called ``off-diagonal nonlinear magnetic susceptibility,'' i.e., we found that for each main crystallographic axis $(a,b$, and $c)$, an additional component of magnetic susceptibility, proportional to the square of the perpendicular to this axis component of $B$, exists. A phenomenological model of this effect, describing the experimental results correctly, was proposed.

CaBi$_2$ is a recently discovered type-I superconductor with $T_c=2$~K and a layered crystal structure. In this work electronic structure, lattice dynamics and electron-phonon interaction are studied, with a special attention paid to the influence of the spin-orbit coupling (SOC) on above-mentioned quantities. We find, that in the scalar-relativistic case (without SOC), electronic structure and electron-phonon interaction show the quasi-two dimensional character. Strong Fermi surface nesting is present, which leads to appearance of the Kohn anomaly in the phonon spectrum and enhanced electron-phonon coupling for the phonons propagating in the Ca-Bi atomic layers. However, strong spin-orbit coupling in this material changes the topology of the Fermi surface, reduces the nesting and the electron-phonon coupling becomes weaker and more isotropic. The electron-phonon coupling parameter $\lambda$ is reduced by SOC almost twice, from 0.94 to 0.54, giving even stronger effect on the superconducting critical temperature $T_c$, which drops from 5.2~K (without SOC) to 1.3~K (with SOC). Relativistic values of $\lambda$ and $T_c$ remain in a good agreement with experimental findings, confirming the general need for including SOC in analysis of the electron-phonon interaction in materials containing heavy elements., Comment: 11 pages, 7 figures, plus Supplemental Material

The exchange-bias (EB) effect with sign reversal was found in $\mathrm{LuF}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ ferrite-chromite, which is a weak ferrimagnet below ${T}_{\mathrm{N}}=265\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, exhibiting antiparallel orientation of the ferromagnetic (FM) moments of the Fe and Cr sublattices due to opposite sign of the Fe-Cr Dzyaloshinskii vector, as compared to that of the Fe-Fe and Cr-Cr. The weak FM moments of the studied compound compensate each other at temperature ${T}_{\mathrm{comp}}=230\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, leading to the net magnetic moment reversal and to observed negative magnetization, at moderate applied fields, below ${T}_{\mathrm{comp}}$. Both vertical and horizontal shifts from the origin were gotten in the field-cooled magnetization hysteresis loops. The EB sign was found to be positive below ${T}_{\mathrm{comp}}$ and negative above ${T}_{\mathrm{comp}}$, with nonmonotonic dependence on cooling field ${H}_{\mathrm{cool}}$. It sharply increases at small values of magnetic fields up to ${H}_{\mathrm{cool}}\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\mathrm{kOe}$, then remains almost unchanged in the range 1--30 kOe and strongly decreases with further increase of ${H}_{\mathrm{cool}}$. This unusual behavior results from the competition of various Dzyaloshinskii-Moriya interactions between $\mathrm{F}{\mathrm{e}}^{3+}$ and $\mathrm{C}{\mathrm{r}}^{3+}$ ions.

Specific heat studies of a series of $R$BaCo${}_{2}$O${}_{5.5}$ $(R=\text{Y}$, Gd, and Tb) layered cobaltites are reported. They were aimed at explaining an influence of different rare-earth ions on thermal properties of these compounds and at studying phase transitions appearing in them. The studies were performed over the temperature range from 3 to 395 K, in the magnetic field ranging from 0 to 9 T. Anomalies accompanying different phase transitions were analyzed. Based on the performed supplementary Raman scattering measurements, frequencies of main optical phonon modes were determined and used for evaluation of the lattice contribution to the specific heat. Lattice, magnon, and Schottky contributions to the specific heat were separated and described theoretically. As a result, the molecular field corresponding to the $R$-Co exchange interactions was estimated to be $\ensuremath{\sim}$1 T.

Magnetization and specific heat of the $S=3∕2$ antiferromagnet on a kagome staircase, ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$, were investigated as a function of temperature and magnetic field. The low temperature magnetization data revealed unusual features related to the strongly frustrated spin lattice. Of particular interest were magnetic field induced phase transitions observed for various orientations of the magnetic field. Abrupt macroscopic magnetization jumps induced by a magnetic field directed along the $\mathbit{c}$-axis have been observed below $6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This effect was also observed for a high enough magnetic field applied in the $\mathbit{a}\text{\ensuremath{-}}\mathbit{c}$ plane. It is suggested that the jump, observed for $H\ensuremath{\parallel}\mathbit{c}$ is due to a spin reorientation phase transition. It was shown that ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ crystals are characterized by a strong magnetocrystalline anisotropy of an easy-plane type. This anisotropy is due to the presence of ${\mathrm{Co}}^{2+}$ ions in octahedral positions.

Specific heat of stoichiometric ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ samples with large ($x=1.0$, 0.9, 0.7, 0.55, 0.45) and low $(x=0.0)$ strontium contents was measured from 3 to 393 K, on heating and on cooling, in zero magnetic field and in the field of 7 T. The temperatures and the orders of particular phase transitions have been determined and the poorly known part of the phase diagram, $1\ensuremath{\geqslant}xg0.6$, has been investigated. The phase transitions from the antiferromagnetic ($x=0.0$, 0.7, 1.0) or ferromagnetic ($x=0.45$, 0.55) to the paramagnetic phase were found to be of the second order, when they were purely magnetic transitions, and of the first order, when they were accompanied by the structural transitions, as for example, the transition from the $C$-type antiferromagnetic to the paramagnetic phase coupled with the transformation from the tetragonal to the cubic structure, occurring in the $x=0.9$ composition. The transitions from the $A$- and $C$-type antiferromagnetic phases to the paramagnetic state were influenced stronger by the magnetic field than the transitions from the $G$-type configuration. This behavior was attributed to the presence of ferromagneticaly ordered nearest neighbors within the $A$ and $C$ configurations and to the presumable quasi one dimensional character of the $C$ configuration, indicated also by quantitatively different critical behavior of the specific heat in this phase. The first order transition from the $A$-type antiferromagnetic to the ferromagnetic phase, coupled with the transformation from the tetragonal to the orthorhombic structure, occurring in the $x=0.55$ sample and accompanied by the $\ensuremath{\delta}$-shaped specific heat anomaly was found to be the most unconventional. It was strongly shifted towards lower temperatures by magnetic field (by $\ensuremath{\sim}33\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at 9 T) without substantial change in the shape of the specific heat anomaly. Supplementary magnetization studies revealed the presence of interesting domain structure effects near this transition. By analysis of the temperature dependences of specific heat, two main parameters characterizing the magnetocaloric effect, isothermal change in entropy and adiabatic change in temperature, have been determined. Near the latter transition they reach $3.4\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕(\mathrm{kg}\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and $\ensuremath{-}1.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively, for the change in magnetic field from 0 to 7 T.

By performing specific heat measurements for a series of the ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ samples ($x=0.12$, 0.135, 0.155, 0.185, and 0.2) several intricacies of the phase diagram have been clarified. For all the samples, specific heat was measured over the temperature range from $2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}380\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in zero magnetic field and in the field of $7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, on heating and on cooling. Additionally, the temperature dependence of specific heat of the $x=0.155$ sample was studied by a heat-flow method in magnetic fields up to $13\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. We show that the phase transition observed below the Curie temperature for the compositions $0.155\ensuremath{\leqslant}x\ensuremath{\leqslant}0.17$ should be interpreted as a structural Jahn-Teller transition as reported in Dabrowski et al. [Phys. Rev. B 60, 7006 (1999)] and not as a charge ordering transition [Liu et al. Phys. Rev. B 64, 144414 (2001)]. Moreover, we show that the Jahn-Teller transition is of the first-order for all the compositions studied and no evolution of its order from the second to the first in the range $0.11\ensuremath{\leqslant}x\ensuremath{\leqslant}0.14$, which was suggested in earlier papers [Liu et al., Phys. Rev. B 64, 144414 (2001)], occurs. Two main parameters characterizing magnitude of the magnetocaloric effect, i.e., the adiabatic change in temperature and the isothermal change in entropy under influence of the external magnetic field, were determined as functions of temperature for all the samples. They were found to be, respectively, $\ensuremath{\sim}4$ and $\ensuremath{\sim}2$ times smaller than those for gadolinium.

Transport, magnetic, and thermal properties of phase-separated ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}\mathrm{Mn}{\mathrm{O}}_{3}$ crystal were studied in a wide temperature range down to $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At low temperatures below the Curie point ${T}_{C}=184\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the sample resistance is characterized by spontaneous transitions to higher resistivity metastable states. Metastability becomes more pronounced when enforced by the application of current pulses at low temperatures. Metastable states are characterized by long-term memory surviving even thermal cycling to room temperatures. Only heating to $Tg{T}_{e}\ensuremath{\approx}350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ erases the previously imprinted state of the system. At temperatures close to the low temperature resistivity maximum, a slow relaxation of the resistance has been observed following changes in the bias current. Ac susceptibility, low-field magnetization, and specific heat data indicate that there is a spin-cluster glass-like transition at temperatures corresponding to the maximum of the relaxation time. Phase separation and coexistence of metallic and insulating ferromagnetic phases with different orbital order at a wide temperature range are claimed to be responsible for the observed electric-field and current effects. The disappearance of the resistance memory effects at temperatures above ${T}_{e}$ may be considered an indirect proof for the existence of one more temperature scale in disordered manganites.

The $\mathrm{Ce}{\mathrm{Ni}}_{4}\mathrm{Al}$ compounds have been studied using the magnetic susceptibility, specific heat, electrical resistivity and x-ray photoemission spectroscopy (XPS) measurements. The XPS experiments were supported by the theoretical calculations employing the TB LMTO method. The estimation of the hybridization, $\ensuremath{\Delta}$, between the $f$-level and the conduction states was based on the XPS measurements of the $\mathrm{Ce}(3d)$ states and revealed a small value of $\ensuremath{\Delta}\ensuremath{\approx}37\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ accompanied by a nearly full $f$-occupancy $({n}_{f}\ensuremath{\approx}0.88)$. The temperature measurements of the dc susceptibility have shown paramagnetic behavior fulfilling the Curie-Weiss law with ${\ensuremath{\mu}}_{\mathrm{eff}}=0.6{\ensuremath{\mu}}_{\mathrm{B}}∕\mathrm{f.u}$. Experimental values of the specific heat coefficient $\ensuremath{\gamma}=29\phantom{\rule{0.3em}{0ex}}{\mathrm{mJK}}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}$ and the Debye temperature ${\ensuremath{\theta}}_{D}=315\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ have been obtained. The electrical resistivity measurements revealed a presence of a minimum at about $16\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.