Magnetic Heat Capacity Research Articles

Magnetoelectric effect in the honeycomb-lattice antiferromagnet BaNi2(PO4)2

We report a comprehensive investigation of the structural, magnetic, and electrical properties in a quasi-two-dimensional planar antiferromagnet ${\mathrm{BaNi}}_{2}{({\mathrm{PO}}_{4})}_{2}$, which crystallizes in the rhombohedral structure (space group $R\overline{3}$) consisting of honeycomb layers of ${\mathrm{Ni}}^{2+}$ ions. Magnetic susceptibility and heat capacity data reveal a long-range antiferromagnetic ordering of ${\mathrm{Ni}}^{2+}$ ions at ${T}_{N}=24$ K. Interestingly, an applied magnetic field induces a dielectric anomaly and an electric polarization at ${T}_{N}$ with the polarization proportional to the applied magnetic fields, demonstrating the linear magnetoelectric effect in ${\mathrm{BaNi}}_{2}{({\mathrm{PO}}_{4})}_{2}$ with a coupling coefficient of 1.67 ps/m. It is interesting to note that the magnetic symmetry associated with the magnetoelectric effect is ${\overline{1}}^{\ensuremath{'}}$, which allows all tensor elements of the magnetoelectric susceptibility.

Magnetic structure investigation of the intercalated transition metal dichalcogenide V1/3NbS2

We investigate the temperature evolution of the magnetic structure of ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ using neutron diffraction techniques. We find that ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ has two propagation vectors: ${\mathbf{k}}_{\mathbf{0}}=(0,0,0)$ and ${\mathbf{k}}_{\mathbf{1}}=(0,0,\frac{1}{3})$. The ${\mathbf{k}}_{\mathbf{0}}$ vector can be associated with an antiferromagnetic ordering of in-plane moments with a refined value of $0.90(5){\ensuremath{\mu}}_{\mathrm{B}}$, and ${\mathbf{k}}_{\mathbf{1}}$ can be associated with moments along the $c$ axis in an up-down-down configuration with refined values of $1.21(12){\ensuremath{\mu}}_{\mathrm{B}}$ and $0.61(6){\ensuremath{\mu}}_{\mathrm{B}}$. Both ${\mathbf{k}}_{\mathbf{0}}$ and ${\mathbf{k}}_{\mathbf{1}}$ magnetic components couple with an out-of-plane ferromagnetic moment consistent with magnetization data. Furthermore, single-crystal neutron diffraction shows evidence of diffuse magnetic scattering between the (010) and ($01\ifmmode\pm\else\textpm\fi{}\frac{1}{3}$) Bragg peaks. We also characterize the field and temperature evolution of the magnetic structure in ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ by magnetic susceptibility and heat capacity measurements. The dc susceptibility measurements give an antiferromagnetic transition temperature of ${T}_{\mathrm{N}}=50$ K, and the field scans reveal that the moment does not saturate at magnetic fields up to 100 kOe.

Possible multiband superconductivity in the quaternary carbide YRe2SiC

We report for the first time the occurrence of superconductivity in the quaternary silicide carbide YRe2SiC with T c ≈ 5.9 K. The emergence of superconductivity was confirmed by means of magnetic susceptibility, electrical resistivity, and heat capacity measurements. The presence of a well-developed heat capacity feature at T c confirms that superconductivity is a bulk phenomenon, while a second feature in the heat capacity near 0.5T c combined with the unusual temperature dependence of the upper critical field H c2(T) indicate the presence of a multiband superconducting state. Additionally, the linear dependence of the lower critical field H c1 with temperature resemble the behavior found in compounds with unconventional pairing symmetry. Band structure calculations reveal that YRe2SiC could harbor a non-trivial topological state and that the low-energy states occupy multiple disconnected sheets at the Fermi surface, with different degrees of hybridization, nesting, and screening effects, therefore making unconventional multiband superconductivity plausible.

Dynamical ground state in the XY pyrochlore Yb2GaSbO7

The magnetic ground state of the pyrochlore Yb2GaSbO7 has not been established. The persistent spin fluctuations observed by muon spin-relaxation measurements at low temperatures have not been adequately explained for this material using existing theories for quantum magnetism. Here we report on the synthesis and characterisation of Yb2GaSbO7 to revisit the nature of the magnetic ground state. Through DC and AC magnetic susceptibility, heat capacity, and neutron scattering experiments, we observe evidence for a dynamical ground state that makes Yb2GaSbO7 a promising candidate for disorder-induced spin-liquid or spin-singlet behaviour. This state is quite fragile, being tuned to a splayed ferromagnet in a modest magnetic field μ0Hc ~ 1.5 T.

Magnetic phase transition and lattice dynamic features in ErB2C borocarbide

A sample of erbium borocarbide ErB2C was synthesized from a stoichiometric mixture of erbium, boron, and pyrographite hydride. Temperature dependent magnetic susceptibility, heat capacity and lattice parameters of borocarbide at 2–300 K were experimentally investigated, the Raman spectrum was determined and analyzed. Sharp anomalies in the heat capacity and magnetic properties of ErB2C near T = 16.3 K, caused by the transition to the antiferromagnetic state, as well as diffuse anomalies at a higher temperature, caused by the effect of the crystal field (Schottky anomalies) were revealed. It was found that the magnetic phase transition does not cause measurable anomalies in the lattice parameters of borocarbide due to the weak coupling between the Er3+ ion subsystem and the B–C layers. Almost zero thermal expansion of erbium borocarbide in the basal plane (along a and b axes) (anisotropic invar effect) as well as an unusual character of the c-axis thermal expansion were observed. The first of these features is due to the high bonding energy in the B–C layers and the weak bond between the layers in the borocarbide crystal lattice. It was found that the anomalous expansion along the c axis is a consequence of the action of the crystal field. The splitting scheme for the ground level of Er3+ ions by crystal field was determined from the analysis of the Schottky anomaly of the heat capacity.

Physical properties of (Mn1−xCox)Si at x≃0.060–0.100 : Quantum criticality

We have grown and characterized three samples of Co doped MnSi and studied their physical properties (magnetization and magnetic susceptibility, heat capacity and electrical resistance). All three samples show non-Fermi liquid physical properties. From literature data and current results follow that impurities (Co and Fe) eliminate the first order phase transition peaks and spread the fluctuation maxima in such a way that its low temperature part effectively reaches the zero temperature, where the fluctuations inevitably become quantum. The behavior of low temperature branches of the heat capacity of the samples suggests that a gradual transition from classical to quantum fluctuations can be described by a simple power function of temperature with the exponent less than one. The $d\rho/dT$ data generally support this suggestion. The values of the heat capacity exponents immediately lead to the diverging ratio $C_p/T$ and hence to the diverging effective electron mass. We found out that at large concentration of the dopant there are no distinct phase transition points. What we observe is a cloud of the helical fluctuations spreading over a significant range of concentrations and temperatures, which become quantum close to 0~K.

Magnetic Properties of S = 1/2 Distorted Kagome Antiferromagnet CdCu3(OH)6Cl2 with Low-Symmetry Orbital Arrangement

The magnetic properties of the S = 1/2 distorted kagome antiferromagnet CdCu3(OH)6Cl2 have been studied by magnetic susceptibility, heat capacity, and high-field magnetization measurements. The mag...

Low-dimensional magnetism of BaCuTe2O6

X-ray diffraction, thermodynamic measurements, and density-functional band-structure calculations are used to study the magnetic behavior of BaCuTe$_{2}$O$_{6}$, a member of the $A$CuTe$_2$O$_6$ structural family that hosts complex three-dimensional frustrated spin networks with possible spin-liquid physics. Temperature-dependent magnetic susceptibility and heat capacity of the Ba compound are well described by the one-dimensional spin-$\frac12$ Heisenberg chain model reminiscent of the Sr analog SrCuTe$_2$O$_6$. While the intrachain coupling $J/k_{\rm B}\simeq 37$ K is reduced compared to 49 K in the Sr compound, the N\'eel temperature increases from 5.5 K (Sr) to 6.1 K (Ba). Unlike the Sr compound, BaCuTe$_2$O$_6$ undergoes only one magnetic transition as a function of temperature and shows signatures of weak spin canting. We elucidate the microscopic difference between the Sr and Ba compounds and suggest that one of the interchain couplings changes sign as a result of negative pressure caused by the Sr/Ba substitution. The N\'eel temperature of BaCuTe$_2$O$_6$ is remarkably insensitive to the magnetic dilution with Zn$^{2+}$ up to the highest reachable level of about 20%.

Effect of structural disorder on the Kitaev magnet Ag3LiIr2O6

The search for an ideal Kitaev spin liquid candidate with anyonic excitations and long-range entanglement has motivated the synthesis of a new family of intercalated Kitaev magnets such as ${\mathrm{H}}_{3}\mathrm{Li}{\mathrm{Ir}}_{2}{\mathrm{O}}_{6}$, ${\mathrm{Cu}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$, and ${\mathrm{Ag}}_{3}\mathrm{Li}{\mathrm{Ir}}_{2}{\mathrm{O}}_{6}$. The absence of a susceptibility peak and a two-step release of the magnetic entropy in these materials have been proposed as evidence of proximity to the Kitaev spin liquid. Here we present a comparative study of the magnetic susceptibility, heat capacity, and muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) between two samples of ${\mathrm{Ag}}_{3}\mathrm{Li}{\mathrm{Ir}}_{2}{\mathrm{O}}_{6}$ in the clean and disordered limits. In the disordered limit, the absence of a peak in either susceptibility or heat capacity and the lack of zero-field muon precession in the $\ensuremath{\mu}\mathrm{SR}$ signal give the impression of a proximate spin liquid state. However, in the clean limit, peaks are resolved in both susceptibility and heat capacity, and spontaneous oscillations appear in the $\ensuremath{\mu}\mathrm{SR}$ signal, confirming long-range antiferromagnetic order in the ground state. The $\ensuremath{\mu}\mathrm{SR}$ oscillations fit to a Bessel function, characteristic of incommensurate order, as reported in the parent compound $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$. Our results clarify the role of structural disorder in the intercalated Kitaev magnets.

Superconductivity in the Z2 kagome metal KV3Sb5

Here we report the observation of bulk superconductivity in single crystals of the two-dimensional kagome metal KV$_3$Sb$_5$. Magnetic susceptibility, resistivity, and heat capacity measurements reveal superconductivity below $T_c = 0.93$K, and density functional theory (DFT) calculations further characterize the normal state as a $\mathbb{Z}_2$ topological metal. Our results demonstrate that the recent observation of superconductivity within the related kagome metal CsV$_3$Sb$_5$ is likely a common feature across the AV$_3$Sb$_5$ (A: K, Rb, Cs) family of compounds and establish them as a rich arena for studying the interplay between bulk superconductivity, topological surface states, and likely electronic density wave order in an exfoliable kagome lattice.

Critical behaviour and renormalization of magnetic entropy change in La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) ceramics

The critical behaviour and magnetic field dependence of magnetic entropy changes (ΔSM) for the ferromagnetic La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) ceramics are systematically investigated in details. Upon Cr doping, the Curie temperature TC, ΔSM and the critical exponents (β, γ, and δ) are substantially influenced. As a result, the TC varies from 330 K for x = 0 to 275 K for x = 0.15 and the ΔSM decreases gradually with higher Cr substitution. The values of the critical exponents of the prepared samples lie between the Tricritical mean field model and 3D-Ising model. Thus, these results suggest that critical phenomena in La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) could not be explained on the conventional universality classes. However, the obtained results suggest an existence of FM short-range order in the prepared samples. To check the agreement with the scaling theory, m = f ± (h) is plotted for all samples. It was found that all data points fall into two separate branches above and below the critical temperature, TC, which confirmed that the critical exponents are reliable. The analysis of the field dependence of the ΔSM reveals the power law dependence at the transition temperature. Based on the value of critical exponents, one can find that all the magnetic entropy changes and heat capacity changes fall on a master curve for all measured fields and temperatures confirming the nature of second-order magnetic transition. This excellent overlap clearly indicates that the critical exponents obtained for the prepared system are reasonably accurate.

Quasi-one-dimensional magnetism in the spin- 12 antiferromagnet BaNa2Cu(VO4)2

We report synthesis and magnetic properties of quasi-one-dimensional spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain compound BaNa$_2$Cu(VO$_4$)$_2$. This orthovanadate has a centrosymmetric crystal structure, $C2/c$, where the magnetic Cu$^{2+}$ ions form spin chains. These chains are arranged in layers, with the chain direction changing by 62$^0$ between the two successive layers. Alternatively, the spin lattice can be viewed as anisotropic triangular layers upon taking the inter-chain interactions into consideration. Despite this potential structural complexity, temperature-dependent magnetic susceptibility, heat capacity, ESR intensity, and NMR shift agree well with the uniform spin-$1/2$ Heisenberg chain model with an intrachain coupling of $J/k_{\rm B} \simeq 5.6$ K. The saturation field obtained from the magnetic isotherm measurement consistently reproduces the value of $J/k_{\rm B}$. Further, the $^{51}$V NMR spin-lattice relaxation rate mimics the 1D character in the intermediate temperature range, whereas magnetic long-range order sets in below $T_{\rm N} \simeq 0.25$ K. The effective interchain coupling is estimated to be $J_{\perp}/k_{\rm B} \simeq 0.1$ K. The theoretical estimation of exchange couplings using band-structure calculations reciprocate our experimental findings and unambiguously establish the 1D character of the compound. Finally, the spin lattice of BaNa$_2$Cu(VO$_4$)$_2$ is compared with the chemically similar but not isostructural compound BaAg$_2$Cu(VO$_4)_2$.

Magnetocaloric and heat capacity studies on NdFe0.5Mn0.5O3

The bulk magnetization, magnetocaloric effect, and heat capacity of polycrystalline NdFe0.5Mn0.5O3 have been studied in the temperature range of 1.5–300 K. The magnetic entropy change (ΔSM) shows a peak near 7 K at 100 kOe with a value of ∼7.22 J kg−1 K−1. Another magnetic entropy change is also observed between 0 and 40 kOe near the spin reorientation region of Fe3+/Mn3+ ions (∼45 K), wherein the entropy change gets suppressed with increasing field. The magnetic heat capacity shows a broad hump near the Néel temperature (∼250 K). Around 5 K, a step-like feature in heat capacity due to the Schottky effect is observed which is associated with the crystal field effects in Nd3+ ions.

Magnetic impurity in a triple-component semimetal

We investigate the effects of a magnetic impurity in a multiband touching fermion system, specifically, a triple-component semimetal with a flat band, which can be realized in a family of transition metal silicides (CoSi family). When the chemical potential coincides with the flat band, it is expected that the impurity response of this system will be very different from that of an ordinary Dirac or Weyl semimetal of which the density of states at the Fermi level vanishes. We first determine the phase diagram within the mean-field approximation. Then, we study the local moment regime by employing two different methods. In the low temperature regime, the Kondo screening is analyzed by the variational wavefunction approach and the impurity contributions to the magnetic susceptibility and heat capacity are obtained, while at higher temperature, we use the equation of motion approach to calculate the occupation number of the impurity site and the impurity magnetic susceptibility. The results are compared and contrasted with those in the usual Fermi liquid and the Dirac/Weyl semimetals.

Calculation of relative dispersions of magnetization, susceptibility, and heat capacity in a two-dimensional weakly diluted Potts model based on computer simulation methods

The Monte Carlo method was used to calculate the relative dispersions of the magnetization Rm, susceptibility Rχ, and heat capacity RC for a weakly diluted impurity Potts model with the number of spin states q = 4. It is shown that the introduction of disorder in the form of nonmagnetic impurities into the two-dimensional Potts model with q = 4 on square lattice leads to nonzero values for Rm, Rχ, and RC at the critical point.

Structure, Magnetism, and First-Principles Modeling of the Na0.5La0.5RuO3 Perovskite

High-purity polycrystalline Na0.5La0.5RuO3 was synthesized by a solid-state method, and its properties were studied by magnetic susceptibility, heat capacity, and resistivity measurements. We find it to be an orthorhombic perovskite, in contrast to an earlier report, with random La/Na mixing. With a Curie–Weiss temperature of −231 K and an effective moment of 2.74 μB/mol Ru, there is no magnetic ordering down to 1.8 K. A broad hump at 1.4 K in the heat capacity, however, indicates the presence of a glassy magnetic transition, which we attribute to the influence of the random distribution of Na and La on the perovskite A-sites. Comparison to CaRuO3, a structurally ordered ruthenate perovskite with a similar A-site ionic radius and magnetic properties, is presented. First-principles calculations indicate that the Na–La distribution determines the local magnetic exchange interactions between Ru ions, favoring either antiferromagnetic or ferromagnetic coupling when the local environment is Na- or La-rich. Thus, our data and analysis suggest that mixing cations with different charges and sizes on the A-site in this perovskite results in magnetic frustration through a balance of local magnetic exchange interactions.

Disentangling the magnetic dimensionality of an alleged magnetically isolated cuprate spin-ladder CuHpCl system: a long-lasting issue.

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.

Multifunctional properties of {CuLn} systems involving nitrogen-rich nitronyl nitroxide: single-molecule magnet behavior, luminescence, magnetocaloric effects and heat capacity.

A series of nitrogen-rich nitronyl nitroxide radical PPNIT (1)-based (PPNIT = 2-(1-(pyrazin-2-yl)-1H-pyrazole)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) 3d-4f ring-shaped tetranuclear clusters [Ln2Cu2(hfac)10(PPNIT)2(H2O)2]·CHCl3 (LnIII = Gd 2, Tb 3, Dy 4; hfac = hexafiuoroacetylacetonate) with multifunctional properties were isolated. The magnetic behavior, luminescence and heat capacity of the 3d-4f complexes were investigated, displaying interesting multiple properties of the molecular materials. The Gd derivative shows a magnetocaloric effect with the maximum entropy change (-ΔSm) of 15.3 J kg-1 K-1 at 2 K for ΔH = 70 kOe. The Tb cluster exhibits spin glass behavior and the characteristic fluorescence emission of the TbIII ion, while the Dy cluster exhibits SMM behaviour, and the heat capacity has been investigated. Notably, in nitronyl nitroxide radical-metal systems, the investigation of diverse properties is still scarce so far. This work can pave the way towards the synthesis of multifunctional materials that combine SMM behavior, and optical or/and thermodynamic properties.

Influence of the interparticle interaction of the ensemble of immobilized superparamagnetic ferroparticles on the static, magnetic and thermodynamic properties of the system

This paper presents a study of the effect of the interparticle dipole-dipole interaction on the static, thermodynamic, and magnetic properties of the ensemble of stationary superparamagnetic particles in the external magnetic field. The relaxation of the magnetic moment of the model ferroparticles occurred by the Neel mechanism. The directions of the easy axes of all particles were assumed to be parallel to each other, but at the angle to the direction of the external magnetic field. The direction of the easy axes was described using the polar and azimuth angles. The potential energy of the system includes a single-particle dipole-axial interaction, a single-particle dipole-field interaction and long-range interparticle dipole-dipole correlations. In the system, two variants of the distribution of ferroparticles over the volume of the container are considered: in the nodes of a simple cubic lattice and randomly. The described model is studied theoretically by expanding the Helmholtz free energy into a classical virial series up to the second virial coefficient. Using the new theory, the contribution of dipole-dipole interactions in the changes in the magnetic susceptibility, magnetization, and heat capacity of the system is estimated, and the results are represented graphically. Important information necessary to the development and synthesis of new magnetic materials with controlled properties is provided.

Фазовые переходы и фазовые превращения в нанообластях фазового расслоения в мультиферроике ErMn-=SUB=-2-=/SUB=-O-=SUB=-5-=/SUB=-

The effect of the rare-earth ion Er3+, which has a large orbital contribution to the magnetic moment, were studied to phase transitions and phase transformations of 2D nanoregions of phase separation in the ErMn2O5 multiferroic. These nanoregions are the semiconductor heterostructures (superlattices) and are formed due to self-organization processes in the ErMn2O5 matrix. Significant effect of Er3+ ions, the moments of which are rigidly oriented along the c axis of the crystal, on the magnetic dynamics, heat capacity and multiferroic properties of layers superlattises was found at a wide temperature range 5 K - 300 K in ErMn2O5 multiferroics.