EuCo2P2: A model molecular-field helical Heisenberg antiferromagnet

We report magnetic susceptibility (chi) and heat capacity Cp measurements along with ab-initio electronic structure calculations on PbCuTe2O6, a compound made up of a three dimensional 3D network of corner-shared triangular units. The presence of antiferromagnetic interactions is inferred from a Curie-Weiss temperature (theta_CW) of about -22 K from the chi(T) data. The magnetic heat capacity (Cm) data show a broad maximum at T^max ~ 1.15 K (i.e. T^max/theta_CW ~ 0.05), which is analogous to the the observed broad maximum in the Cm/T data of a hyper-Kagome system, Na4Ir3O8. In addition, Cm data exhibit a weak kink at T^* ~ 0.87 K. While the T^max is nearly unchanged, the T^* is systematically suppressed in an increasing magnetic field (H) up to 80 kOe. For H > 80 kOe, the Cm data at low temperatures exhibit a characteristic power-law (T^{\alpha}) behavior with an exponent {\alpha} slightly less than 2. Hopping integrals obtained from the electronic structure calculations show the presence of strongly frustrated 3D spin interactions along with non-negligible unfrustrated couplings. Our results suggest that PbCuTe2O6 is a candidate material for realizing a 3D quantum spin liquid state at high magnetic fields.

Lanthanide ($Ln$) based $Ln\mathrm{SbTe}$ materials have garnered significant attention due to the rich interplay of long-range magnetic ordering and topological properties, driven by unique crystalline symmetry, $4f$ electron interactions, and pronounced spin-orbit coupling (SOC) effects. DySbTe, as a heavier lanthanide based member of the $Ln\mathrm{SbTe}$ family, stands out with its SOC and larger on-site interactions on its $4f$ electrons, which arise due to the heavier Dy element. Here, we present a comprehensive study on the low-temperature bulk physical properties and the electronic structure of DySbTe using magnetic susceptibility, heat capacity, and electrical resistivity measurements, along with high-resolution angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy and spectroscopy (STM/S), and density functional theory calculations. Our thermodynamic measurements revealed an antiferromagnetic ordering below ${T}_{\mathrm{N}}=7.45$ K and a subsequent magnetic phase transition at ${T}_{\mathrm{N}1}=7.15$ K. Our transport studies indicate a semimetallic behavior with unusual feature in the ordered state. Our ARPES measurements revealed a diamond-shaped Fermi pocket centered at the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point, with band features that evolve distinctly across various binding energies. STM/S results indicate a minimum in the density of states at around 100 meV below the Fermi level, and ARPES measurements reveal a significant gap present around the $\overline{\mathrm{X}}$ point, differentiating DySbTe from other $Ln\mathrm{SbTe}$ compounds. These findings enhance our understanding of the SOC effects on the electronic structure and topological properties in the $Ln\mathrm{SbTe}$ family, highlighting DySbTe as a promising candidate for exploring the interplay between topology and magnetism.

The Cu2(1,4-diazacycloheptane)2Cl4 (CuHpCl) crystal is a molecular transition metal antiferromagnetic complex, whose magnetism has been a long-lasting issue. The outcome of a variety of experimental studies (on magnetic susceptibility, heat capacity, magnetization, spin gap and INS) reported many different J values depending on the fitting ladder model used. From all available experimental data, one can infer that CuHpCl is a very complex system with many competing microscopic magnetic JAB interactions that lead to its overall antiferromagnetic behavior. A first-principles bottom-up study of CuHpCl is thus necessary in order to fully disentangle its magnetism. Here we incorporate data from ab initio computations providing the magnitude of the JAB interactions to investigate the microscopic magnetic couplings in CuHpCl and, ultimately, to understand the macroscopic magnetic behavior of this crystal. Strikingly, the resulting magnetic topology can be pictured as a 3D network of interacting squared plaquette magnetic building blocks, which does not agree with the suggested ladder motif (with uniform rails) that arises from direct observation of the crystal packing. The computed magnetic susceptibility, heat capacity and magnetization data show good agreement with the experimental data. In spite of this agreement, only the calculated magnetization data are used to discriminate between the different spin regimes in CuHpCl, namely gapped singlet, partially polarized and fully polarized phases. Additional analysis of the magnetic wavefunction enables the conclusion that long-range spin correlation can be discarded as being responsible for the partially polarized phase, whose magnetic response is in fact due to the complex interplay of the magnetic moments in the 3D magnetic topology.

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.

The iodate anion group has been widely used for design and synthesis of functional materials including nonlinear optical materials but rarely for magnetic materials. Particularly, none of magnetic iodate fluorides has been reported yet. In this work, first, two novel magnetic iodate fluorides MIO3F (M = Co 1 and Ni 2) have been synthesized by a hydrothermal method and characterized by magnetic susceptibility, magnetization, and heat capacity measurements as well as thermogravimetry, Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy. Compounds 1 and 2 are isostructural and crystallize in the monoclinic space group P21/n with alternating M2+-F2-M2+-O2-M2+ zigzag spin chains along the b axis, which are further separated by triangular IO3 groups in the ab plane. Magnetic susceptibilities suggest that 1 exhibits an antiferromagnetic long-range order (LRO) at 16.5 K, confirmed by heat capacity results with released entropy consistent with the theoretical value for a pseudo-spin of 1/2 for Co2+ at low temperatures. Meanwhile, 2 displays a broad maximum around 10.5 K for low dimensional magnetism followed by a sharp peak at 5.7 K indicating the occurrence of an LRO transition, in good agreement with the heat capacity measurement. Field-dependent magnetizations show an obvious spin-flop transition around 4.5 T and a magnetic hysteresis loop between 4.5 and 7 T for 1, but only a slight slope change could be observed around 2.3 T for 2. Thermal stability, FT-IR, and UV-vis-NIR spectroscopy of 1 and 2 are also reported.

The title compound is characterized by magnetic susceptibility, magnetization, heat capacity, electrical resistivity, and magnetoresistivity measurements.

We present electron spin resonance (ESR) measurements in single-crystalline samples of EuIn${}_{2}$As${}_{2}$ grown using the In-flux method. This compound crystallizes in a hexagonal P6(3)/$mmc$ structure and presents antiferromagnetic (AFM) ordering below ${T}_{N}=16$ K. In the paramagnetic state, a single Eu${}^{2+}$ Dysonian ESR line with nearly temperature-independent $g$-factor and linewidth is observed, indicating the absence of Korringa-like relaxation of the Eu${}^{2+}$ ions. Approaching the AFM transition, we observe an anisotropic $g$-shift and a linewidth broadening which has a maximum at ${T}_{N}$, suggesting that the short-range AFM correlation dominates the spin dynamics of the Eu${}^{2+}$ spins in this temperature range. Our results are discussed based on complementary data (magnetic susceptibility, heat capacity, and electrical resistivity measurements) that provide further details about the global macroscopic physical properties of the EuIn${}_{2}$As${}_{2}$ intermetallic compound.

Magnetic susceptibility and heat capacity measurements as a function of temperature on a single-crystal sample of a spin-ladder material, Na2Co2(C2O4)3(H2O)2, are reported. Principal susceptibilities, parallel and perpendicular to the ladder direction, respectively, show broad maxima around 22 and 17 K. Both susceptibilities decay exponentially down to about 5 K and thereafter they are essentially independent of temperature. These findings amount to a signature of a quantum phase transition from a spin-liquid to Néel ordered state previously predicted theoretically. No anomaly is found in the heat capacity around the transition temperature.

Magnetic properties of CoCl 2-intercalated graphite

Subject of research: the article presents studies of the properties of solid solutions V2Me0,02O3 in the metaldielectric phase transition region.
 Purpose of research: to obtain temperature dependences of physical parameters (heat capacity, electrical resistance, magnetic susceptibility) of samples of the composition V2Me0,02O3 in the range of 60-400 K; to determine the effect of vanadium concentration and the type of alloying element on the parameters of the phase transition and the parameters of the energy spectrum of the crystal lattice.
 Methods and objects of research: the objects of research were solid solutions based on vanadium oxide V2O3, alloyed with aluminum, iron, chromium. Doping was used to regulate and stabilize the parameters of the V2O3 phase transition. The temperature of the phase transition was determined by measuring the temperature dependences of heat capacity, electrical resistance and magnetic susceptibility.
 Main results of research: in the course of experimental studies, it was found that the temperatures of metaldielectric phase transitions determined by different methods are close in their values. The dependences of the phase transition temperature on the parameters of the crystal lattice, changes in magnetic susceptibility for pure and doped vanadium oxide, as well as the dependence of the transition temperature and the electrical resistivity jump on the Debye temperature are obtained. The influence of alloying metals and vanadium concentration on the properties of the studied samples in the phase transition region was determined by the temperature dependences of magnetic susceptibility, electrical resistance and heat capacity.

In this paper, we report on the discovery of a spinel compound, Co0.7Al2S4, which was synthesized at high-pressure. The systematic characterizations were carried out by structural, magnetic, and heat capacity measurements. The compound crystallizes into a cubic structure with the space group Fd3̅m (no. 227) and the lattice constant a = 9.9580(1) Å. Magnetic susceptibility measurements suggest that Co0.7Al2S4 exhibits a spin glass ground state, freezing at Tf ∼ 7.2 K with a Weiss temperature Tθ ∼ -115.9 K, which is verified by ac magnetic susceptibility and heat capacity measurements. The frustration parameter f for Co0.7Al2S4 is calculated to be about 16.6, based on the formula f = | Tθ/Tf |, indicating that Co0.7Al2S4 is a high-frustration magnet. Specific heat data displays a T2 dependence below the freezing temperature, which is different from the linear dependence observed in a common spin glass system. Compared with the similar compound CoAl2O4, it is suggested that the vacancies in the Co sites should be responsible for the occurrence of the spin glass behavior of Co0.7Al2S4.

Magnetic susceptibility and heat capacity of graphene in two-band Harrison model

Intermediate valence state of cerium in CeNi

We report the synthesis and the magnetic properties of single crystalline CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$ and their non magnetic La-analogs. The single crystals of these quaternary compounds were grown using Al-Si binary eutectic as flux. The anisotropic magnetic properties of the cerium compounds were explored in detail by means of magnetic susceptibility, isothermal magnetization, electrical resistivity, magnetoresistivity and heat capacity measurements. Both CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$ undergo two antiferromagnetic transitions, first from the paramagnetic to an antiferromagnetic state at $T_{\rm N1}$~=~12.6~K and 15.5~K, followed by a second transition at lower temperatures $T_{\rm N2}$~=~9.4~K and 13.8~K, respectively. The paramagnetic susceptibility is highly anisotropic and its temperature dependence in the magnetically ordered state suggests the $c$-axis to be the relatively easy axis of magnetization. Concomitantly, isothermal magnetization at 2~K along the $c$-axis shows a sharp spin-flop transition accompanied by a sizeable hysteresis, while it varies nearly linearly with field along the [100] direction up to the highest field 14~T, of our measurement. The electrical resistivity provides evidence of the Kondo interaction in both compounds, inferred from its $-lnT$ behavior in the paramagnetic region. The heat capacity data confirm the bulk nature of the two magnetic transitions in each compound, and further confirm the presence of Kondo interaction by a reduced value of the entropy associated with the magnetic ordering. From the heat capacity data below 1~K, the coefficient of the linear term in the electronic heat capacity, $\gamma$, is inferred to be 195.6 and 49.4~mJ/mol K$^2$ in CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$, respectively classifying these materials as moderate heavy fermion compounds.

One-dimensional quantum statistics has been studied at the limit of isotropic exchange interaction in the unpaired electron system of a ferromagnetic organic radical crystal, 3-(4-chlorophenyl)-1,5-diphenyl-6-oxoverdazyl. The characteristic field dependence of the magnetic heat capacity of this crystal is quantitatively explained by the theoretical values derived from the Bethe-ansatz technique applied to the quantum transfer matrix, with a unique intrachain exchange constant J / k B =5.5 K. By the simultaneous measurement of magnetic susceptibility and heat capacity, the three-dimensional ordering at T c =0.21 K, which is triggered by a weak interchain coupling ∣ z J '∣/ k B =3×10 -2 K, is confirmed.