The structure of Cu(tn)Cl2 (tn = C3H10N2 =1, 3 - diaminopropane) contains a carbon disorder within tn ligands that transforms at low temperatures into a modulation of tn within supercells. Strong quantum fluctuations, likely arising from competition between different magnetic orderings within quasi-two-dimensional structural domains of the supercells, lead to an extreme weakening of long-range magnetic correlations, as indicated by previous studies. This work is focused on the magnetic properties of such a modulated structure. Single-crystal magnetic susceptibility, magnetization, and electron paramagnetic resonance spectra were studied in the fields parallel to the a axis. Strong quantum fluctuations preclude the formation of a spin-glass state and significantly affect the isothermal magnetization of the magnetically ordered phase. Quadratic-like magnetic-field dependence of magnetization in the ordered phase reflects dynamic processes that reduce the polarizing effect of the magnetic field. Electron paramagnetic resonance spectra are characterized by a significant frequency-dependent broadening of the resonance lines, ascribed to staggered fields arising from the alternating tilting of the local octahedra within supercells. Future studies are discussed since this attractive system offers the investigation of a ground state with strong quantum fluctuations in the absence of structural defects introduced by external sources.

Competition between P n O 3 n +1 chains and Zn–O network size allows tuning of thermal conductivity.

Cu(tn)Cl-2(tn=C3H10 N-2) represents a quasi-2D quantum magnet which preserves 2-D features down to mK region despite the setting of magnetic long-range order at 0.55 K. The existence of large quantum fluctuations can be associated with the incommensurate modulated crystal structure. Previous studies of the magnetic phase diagram revealed an additional phase in the vicinity of a critical region. Since the phase appears in the fields perpendicular to the modulation vector, its dependence on the field orientation may have its origin in the spatial and spin anisotropies. The latter can be estimated from the electron paramagnetic resonance (EPR) spectra. The present work is devoted to the X-band single crystal studies of the angular and temperature dependence of EPR spectra. Angular dependence of linewidth within the ab and ac planes shows cos(2)theta dependence associated with the contribution of spin anisotropies. The analysis of the temperature dependence of linewidth along the a - and b -axis enabled the quantitative estimation of spin anisotropies. In the field parallel to a -axis, which is perpendicular to the modulation vector, the linewidth is determined by the combined contribution of exchange-narrowed dipolar coupling, antisymmetric Dzyaloshinskii-Moriya (DM) interaction, and symmetric spin anisotropies of dipolar origin K-dip and exchange anisotropy K(EA) . The absence of the additional phase in the magnetic phase diagram along the b -axis, as well as symmetry requirements, suggests that the DM contribution along the b -axis could be neglected, and the linewidth is dominated by the contribution of symmetric spin anisotropies.

Previous studies showed that partially Cu-doped zeolitic imidazole framework ZIF-8 shows better properties than the parent Zn-based compound (Zn(mIm)2, HmIm = 2-methylimidazole = C4H6N2). Our work is focused on the preparation of ZIF structures with 100 % Cu(II) concentration. Using XRD, EDX, TEM, infrared and Raman spectra, three products have been identified as previously reported Cu-ZIF with 100 % concentration of Cu(II) ions (i.e. Cu(mIm)2), while in other product denoted as compound (1) the major phase was unexpectedly identified as brochantite. In both systems strong magnetic short-range antiferromagnetic correlations associated with the bulk of nanoparticles manifest at high temperatures. In compound (1) with relatively high crystallinity, the surface spins represent <10 % from the total number and this disordered component leads to a pronounced Curie tail in the susceptibility and contributes to nonlinear magnetization at low temperatures. The antiferromagnetic nanoparticles undergo a phase transition to magnetic long-range order with wide distribution of transition temperatures manifested by huge rounding-off effect of the λ-like specific heat anomaly at about 6 K. In Cu-ZIF which is characterized by much smaller nanocrystallites and partial amorphous content, instead of the phase transition to magnetic long-range order, spin glass behavior has been observed at low temperatures. The manifestation of bulk low-dimensional magnetism and disordered spins from surface and amorphous phase was clearly demonstrated in all studied quantities including EPR spectra. The impact of the coexistence of strong short-range correlations at nanoscale and glassy state on the formation of unconventional magnetic ground-state is discussed.

The combination of mean coordination and concentration dependencies of elastic modules and low-frequency Raman scattering of As-S glasses brings new information about the spectroscopic boson peak (SBP) behavior. The analysis of the characteristic temperature positions of the thermometric boson peak (TBP) and the magnitude of heat capacity of As-S glasses was performed. This study was focused on the As-S compounds from the first glass-forming region with particular attention to the compositions of flexible, intermediate, and stressed-rigid phases. The origin of SBP and TBP is expected to have a structural nature. The spectral features found in the super low-frequency region of Raman spectra were assigned to quasi-localized "soft" modes.The sulfur-rich glass, g-As2S5, represents the intermediate phase with AsnSm clusters containing closed ends and several "soft" nanoclusters. These soft clusters can be responsible for intrinsic quasi-localized "soft" modes, the overall rigidity of the system, and quasi-elastic light scattering.

A plateau characterizes the thermal conductivity k(T) of many amorphous materials at temperatures above 1 K together with a maximum in specific heat Cp, called the Boson peak at the same temperature region. It has been believed for over 50 years that those features are the universal property of glasses. Using the analogy of the keystone species concept of ecology, where one species has a disproportionately large effect on its environment relative to its abundance, we will present the impact of keystone nanocluster concentration on low-temperature k(T). Our study is focused on the As-S glassy systems, where each compound represents a different environment. It is shown that the presence of keystone S8 nanoclusters leads to the plateau formation in the k(T) of As2S3 and As2S5 samples. At the same time, the Boson peak in the Cp was preserved, suggesting that nanoclusters contribute to both the k(T) plateau and Cp maximum.

Applying the procedure of a rapid synthesis in the aqueous system, nanocrystalline form of ZIF-8 and Cu-ZIF was obtained. The composition of the latter was inferred from the comparison of vibration spectra and lattice specific heats of both compounds which become nearly identical. The nanocrystalline character of both compounds prevented direct comparison of powder XRD patterns and manifested by the appearance of a boson peak in the diamagnetic ZIF-8 specific heat. The low-temperature magnetic contribution in Cu-ZIF specific heat and a Curie-Weiss tail in low-temperature susceptibility may originate from the effect of surface spins while the round maximum observed in the susceptibility at 135 K indicates the presence of strong low-dimensional correlations with the exchange coupling similar to 200 K. Corresponding magnetic contribution cannot be observed in the specific heat due to the huge overlap by the high-temperature lattice contribution. Negligible magnetization values at low temperatures correspond to the aforementioned strong antiferromagnetic coupling. Future experimental scenarios are discussed which should provide better understanding of the bulk and surface magnetism in this unique quantum system.

The growth of sufficiently large single crystals of $\mathrm{Cu}(tn){\mathrm{Cl}}_{2}$ $(tn=1,3\text{\ensuremath{-}}\text{diaminopropane})$ enabled specific heat and susceptibility studies in various field orientations. The nearly invisible broad hump in zero-field specific heat at 0.6 K coincides with the change in the characteristic parameters of zero-field muon relaxation spectra. The lack of oscillations in the time spectra and their exponential character preserved down to 40 mK suggest the coexistence of static and fluctuating local fields associated with the prevalence of low-dimensional correlations. The extreme two-dimensionality is also manifested by the nonmonotonous character of the magnetic phase diagram. First-principle calculations of exchange couplings introduced a concept of a quasi-two-dimensional magnetic lattice with many couplings within the magnetic layers. The strongest ones lead to the model of a rectangular lattice with the intrachain coupling $J/{k}_{\mathrm{B}}=4.3$ K and the interchain coupling ${J}^{\ensuremath{'}}/J=0.46$, which provides excellent agreement with the zero-field specific heat. However, the susceptibility data suggest the importance of other weaker interactions in accord with first-principle studies. Significant broadening of field-induced specific heat anomalies may be ascribed to potential intrinsic partial magnetic disorder associated with the gradual modulation of $tn$ positions in the crystal structure.

Novel two-dimensional magnetic assembly was designed, manufactured, and its static and dynamic magnetic response was investigated. The assembly contains Fe3O4 nanoparticles of nominal size 7 nm which were deposited on plasma-treated polypropylene substrate using a grafting technique. The nanoparticles create ag-glomerates with size distribution ranging nominally from 10 nm to 110 nm. The temperature dependence of zero -field and field-cooled susceptibility is consistent with glassy behavior. The relative shift of maximum in alter-nating susceptibility & UGamma; & AP;0.075 and z & upsilon; = 10 obtained from critical slowing down analysis also support the formation of the collective states akin to super spin-glass. However, the absence of collapse in dynamic scaling of alternating susceptibility data using predictions for three-dimensional spin-glass with Gaussian distribution of magnetic coupling and two-dimensional bimodal spin-glass suggests that the studied system is not representative of the used limiting models. The investigation of memory effects revealed the coexistence of relaxation phe-nomena of collective degrees of freedom and individual nanoparticles. The obtained results suggest that the studied assembly is appropriate for the investigation of super spin-glass state in two-dimensional magnetic system with dominant dipolar interaction.

The assembly consisting of Fe3O4 nanoparticles deposited on a plasma-treated polypropylene substrate was structurally characterized and its static and dynamic magnetic properties were investigated. The Fe3O4 nanoparticles of the nominal size of 10 nm create agglomerates of the size ranging from nominally 10 to 400 nm which were deposited on the polypropylene substrate using the grafting technique. The behavior of zero field cooled and field cooled susceptibility was found to be consistent with the onset of the super spin-glass state with glassy temperature Tg = 211 K. The formation of the super spin-glass state was also supported by the relative shift of maximum in alternating susceptibility I' approximate to 0.06 and z epsilon = 8.6 obtained from critical slowing down analysis as well as by the study of memory and aging effects. Significant renormalization of Tg and z upsilon for obtaining universal behavior in dynamic scaling of alternating susceptibility is tentatively ascribed to deviation toward two-dimensional magnetic behavior. The obtained results suggest that the studied assembly may be appropriate for the realization of unique two-dimensional super spin glass with dominant dipolar interaction.

The growth of sufficiently large single crystals of Cu(tn)Cl2 (tn=1,3-diaminopropane) enabled specific heat and susceptibility studies in various field orientations. The nearly invisible broad hump in zero-field specific heat at 0.6 K coincides with the change in the characteristic parameters of zero-field muon relaxation spectra. The lack of oscillations in the time spectra and their exponential character preserved down to 40 mK suggest the coexistence of static and fluctuating local fields associated with the prevalence of low-dimensional correlations. The extreme two-dimensionality is also manifested by the nonmonotonous character of the magnetic phase diagram. First-principle calculations of exchange couplings introduced a concept of a quasi-two-dimensional magnetic lattice with many couplings within the magnetic layers. The strongest ones lead to the model of a rectangular lattice with the intrachain coupling J/kB = 4.3 K and the interchain coupling J'/J = 0.46, which provides excellent agreement with the zero-field specific heat. However, the susceptibility data suggest the importance of other weaker interactions in accord with first-principle studies. Significant broadening of fieldinduced specific heat anomalies may be ascribed to potential intrinsic partial magnetic disorder associated with the gradual modulation of tn positions in the crystal structure.

The temperature dependence of the thermal conductivity k(T) of the AsxS100-x glass system was studied down to 1.8 K in a wide range of various (x = 20, 28.6, 40, 45, and 50) compositions. Universal glass anomalies in k(T) were revealed. The temperature dependence k(T) ∼ T2 onset at the lowest temperatures and plateau below 15 K were detected. The plateau formation is sample quality sensitive and composition-dependent. It was experimentally found that even with a slow cooling rate, several samples were cracked. Depending on the sample damage, the additional internal scattering process leads to the k(T) plateau suppression. The observed k(T) temperature dependence is similar to the glassy ceramics-like behavior.

In this work, we present an experimental study to find the optimal way of encapsulation of the magnetic quasi-two-dimensional system Cu(en)(H2O)2SO4 (en = ethylenediamine = C2H8N2) in mesoporous silica SBA-15 with hexagonal pore morphology with a pore size of 5 nm. Our main goal is to achieve the most significant possible degree of pore filling and to study the effect of encapsulation of complex Cu(en)(H2O)2SO4 in SBA-15 silica on the magnetic properties of the studied complex by means of electron paramagnetic resonance (EPR) and magnetization measurements. It was found that the adsorption equilibrium during the adsorption of the Cu(en)(H2O)2SO4 complex from the solution to SBA-15 was reached after only 24 h, and the samples prepared by adsorption for a longer time (72 h, 14 days) did not show an increased amount of the loaded complex. The degree of pore filling represents around 60 % of the total volume of internal pores. The analysis of temperature dependence of susceptibility, the field dependence of magnetization, and EPR spectra showed that due to the encapsulation of Cu(en)(H2O)2SO4 complex in mesoporous silica, the magnetic correlations between Cu(II) ions are significantly weakened, yielding paramagnetic behavior in the studied system.

This work is devoted to the comparative study of the lattice specific heat of Cu(en)(H2O)(2)SO4, Cu(en)(2)SO4 and Cu(en)(2)CrO4, where en = ethylenediamine - C2H8N2. Previous studies on the effects of spatial anisotropy of exchange coupling within the magnetic layer showed that quasi-one-dimensional polymer structures based on Cu(II) ions, Cu(en)(H2O)(2)SO4 and Cu(en)(2)SO4 represent realizations of spin 1/2 Heisenberg model on the spatially anisotropic zig-zag square lattice and the dimerized square lattice, respectively. The substitution of S-Cr in isomorphic Cu(en)(2)SO4 and Cu(en)(2)CrO4 introduces differences in lattice specific heat. The description of the heat capacity of the lattice up to room temperature was carried out considering the contribution of acoustic phonons within the Debye model and optical phonons using Einstein approximation. Deviations of the Debye model from the lattice heat capacity are already observed above 15 K for all compounds, for Debye temperatures theta(D) = 146 K, 101 K and 94 K for Cu(en)(H2O)(2)SO4, Cu(en)(2)SO4 and Cu(en)(2)CrO4, respectively. The effect of acoustic and optical modes on magnetic correlations in these systems is also discussed.

Magnetic susceptibility, magnetization and specific heat of powder and single crystal of Cu(en)2SO4 were investigated. The analysis of the data confirmed that Cu(en)2SO4 can be treated as a quasi-two-dimensional array of magnetic dimers with singlet-ground state persisting up to about 6.5 T. Magnetization and susceptibility studies were performed in the singlet phase and the analysis revealed that g-factor anisotropy is the main mechanism responsible for the different behavior in the magnetic field applied along the b and c axis. The investigation of powder and single crystal specific heat in magnetic fields applied along all three crystallographic directions revealed only small anisotropy associated with the g-factor anisotropy. All mentioned data sets resemble main features of the spin 1/2 HAF dimer model with J/kB = -5.52 K. The observed deviations can be ascribed to the presence of inter-dimer interactions with the effective strength z'J'/kB = -2.7 K. In fields above 6.5 T the system passes from the singlet phase to the ordered state stable up to about 11 T. The expectation of a dome shape magnetic phase diagram is based on the strong dimerization of the magnetic lattice. Future experiments and calculations are discussed to identify the origin of the quantum phase transition associated with the gap closing.

Static and alternating magnetic susceptibility, magnetization, and electron-spin resonance studies of Gd(III) complex [Gd-2(H2O)(6)(C2O4)(3)]center dot 2.5H(2)O enabled its identification as an S = 7/2 magnet with easy-axis anisotropy D/kB = -91.2 mK and magnetic interaction effectively mediated by dipolar coupling |J/kB| approximate to 12 mK. The magnetic field-induced slow relaxation at high temperatures is ascribed to direct relaxation with a pronounced effect of phonon bottleneck and Raman process. In contrast, relaxation at low temperatures displays recipro-cating thermal behavior, where spin dynamics accelerates upon cooling. The potential origin of the observed behavior is discussed.

The analysis of specific heat, magnetic susceptibility and magnetization identified the studied compound Cu [C6H2(COO)4][H3N-(CH2)2-NH3]& sdot;3H2O as a quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet on the rectangular lattice with the intrachain coupling J1/kB approximate to 7.39 K and the interaction ratio R approximate to 0.44. A phase transition to a magnetically ordered state was observed in zero magnetic field at TN = 1.28 K. The analysis of magnetic specific heat in non-zero magnetic fields revealed features characteristic of the field-induced Bere-zinskii-Kosterlitz-Thouless phase transition theoretically predicted for ideal two-dimensional magnets. The electron paramagnetic resonance studies of Cu[C6H2(COO)4][H3N-(CH2)2-NH3]& sdot;3H2O revealed the increase of gx and gy and decrease of gz below 25 K due to the presence of dipolar coupling and the exchange anisotropy. The upturn of linewidth appearing below 30 K can be ascribed to the development of intralayer magnetic correlations.

Zeolitic imidazolate frameworks represent new materials falling into the large group of metal-organic frameworks with wide application potential. The present work is focused on the study of fundamental properties of imidazolate compound [{Zn(mIm)(2)center dot 2H(2)O}(infinity)],which is referred in literature as ZIF-8. Measurements of infrared spectra in the mid-infrared and far-infrared regions at room temperature as well as heat capacity in the range from 2 to 300 K were performed. The character of the infrared spectra suggests why the specific heat data values are so small, and even at 300 K the values are much lower than the classical value of 3sR resulting from the equipartition principle. Analysis of the specific heat of the ZIF-8 powder sample within the Debye model including only the contribution of three acoustic phonon branches revealed deviations of the model from experimental data already above 20 K. Low-frequency optical modes as indicated by infrared spectra are responsible for the observed deviations.

An experimental study was conducted to investigate the magnetic properties of dysprosium-doped phosphate glasses. Low-temperature (LT) measurements of the specific heat of Dy(PO3)3 were performed in the range of 0.38-300 K in the magnetic fields up to 9 T. The LT specific heat of amorphous materials is characterized by the presence of a broad maximum named boson peak (BP). The LT specific heat of the Dy-doped sample is dominated by the magnetic contribution, which overlaps the BP. Due to that reason, the specific heat of Y(PO3)3 nonmagnetic glasses was also measured at the same temperature range, revealing the BP at 12-14 K. The magnetic susceptibility was measured from 1.8 K up to room temperature, yielding the effective magnetic moment of 10.65 mu B, which is close to the theoretical prediction for Dy3+. Magnetization curves were measured up to B = 5 T with temperatures ranging from 2 to 50 K. X-band electron-paramagnetic resonance spectra were measured from 0 to 1 T, revealing a maximum at 100 mT. The line achieves maximal intensity at tem-peratures around 12-14 K, which coincides with the appearance of BP in specific heat. The coincidence suggests the presence of the magnetoelastic coupling between the ground quasi-doublet and boson peak.

Comparative analysis of structural and physical properties of Cu(en)Cl2 and Zn(en)Cl2 (en = ethylenediamine) metal-organic compounds was performed. In Cu(en)Cl2 the ethylenediamine coordinates as a typical chelating ligand with carbon disorder, while single crystal X-ray study of Zn(en)Cl2 revealed untypical bridging en ligand with the trans conformation. Infrared and Raman spectra indicate sensitivity of Zn(en)Cl2 to the preparation method. Specific heat of both compounds at temperatures from 2 to 300 K is governed preferentially by low-frequency vibrations of metal chromophores. The appearance of a boson-like peak in Zn(en)Cl2 and observation of Debye-like behavior in Cu(en)Cl2 specific heat suggest qualitative differences in acoustic/optical phonon branches within the Brillouin zone. The appearance of the boson peak in perfect crystals as a potential hallmark of anomalous phonon scattering and its impact on the thermal transport and magnetic properties is discussed.