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• Encapsulation of the magnetic quasi-two-dimensional system Cu(en)(H 2 O) 2 SO 4 in SBA-15. • Weakening of magnetic correlations after encapsulation. • Analysis of the EPR line shape confirmed significant magnetic dilution. In this work, we present an experimental study to find the optimal way of encapsulation of the magnetic quasi-two-dimensional system Cu(en)(H 2 O) 2 SO 4 (en = ethylenediamine = C 2 H 8 N 2) 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)(H 2 O) 2 SO 4 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)(H 2 O) 2 SO 4 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)(H 2 O) 2 SO 4 complex in mesoporous silica, the magnetic correlations between Cu(II) ions are significantly weakened, yielding paramagnetic behavior in the studied system. [ABSTRACT FROM AUTHOR]

• Metal-organic framework ZIF-8 (1) and Cu-ZIF (2) were prepared as nanocrystallites. • Vibration spectra and lattice specific heat of (1) and (2) are the same. • Boson peak identified in the specific heat of (1). • Short-range correlations between surface spins manifest in specific heat below 6 K. • Short-range correlations between bulk spins manifest in susceptibility above 100 K. 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 ∼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. [ABSTRACT FROM AUTHOR]

• Magnetization, susceptibility and specific heat experimentally investigated. • Only g -factor anisotropy is responsible for anisotropy in all data. • All data resemble main features of antiferromagnetic dimer model. • Field-induced ordered state stabilized between 6.5 T and 11 T. • Assumption of a dome shape magnetic diagram due to strong dimerization. Magnetic susceptibility, magnetization and specific heat of powder and single crystal of Cu(en) 2 SO 4 were investigated. The analysis of the data confirmed that Cu(en) 2 SO 4 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 / k B = -5.52 K. The observed deviations can be ascribed to the presence of inter-dimer interactions with the effective strength z'J' / k B = -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. [ABSTRACT FROM AUTHOR]

• Crystal structure suggests formation of magnetic dimers between Cu(II) ions. • Good agreement of experimental data with antiferromagnetic dimer model was observed. • The intra-dimer exchange coupling was estimated J/k B = −5.52 K. • Spin gap ∼11 K is expected to vanish at the critical field 7.8 T. • Absence of phase transition to magnetic long-range order down to 0.4 K. Specific heat, magnetic susceptibility and magnetization of Cu(en) 2 SO 4 single crystal were investigated in the field applied along the b- axis. The analysis of the susceptibility within the Curie-Weiss law indicates the antiferromagnetic nature of the exchange coupling between Cu(II) ions with zJ/k B = −6.4 K. Considering the structure of this material, the formation of magnetic dimers can be expected. Very good description of susceptibility data was achieved using the Heisenberg antiferromagnetic dimer model with intra-dimer coupling J / k B = −5.52 K, effective inter-dimer coupling J ' / k B = −0.3 K and g b = 2.12. The energy gap in the spin excitation spectrum was estimated Δ/ k B ≈ 11 K and corresponding critical field B c b ≈ 7.8 T required for closing the gap. The dimerized nature of magnetic interactions was also confirmed by specific heat and isothermal magnetization data which manifest qualitatively the same behavior as the aforementioned dimer model. The possibility of further low-temperature experiments in the closed gap regime is discussed to obtain more detailed concept of magnetic interactions in this interesting compound. [ABSTRACT FROM AUTHOR]

• Neutron powder diffraction experiments in temperature range 20 mK–300 K. • Completing the magnetic phase diagram of NdMn 1−x Fe x O 3 substitutional system. • X-rays and neutrons used as complementary probe. The low temperature crystal and magnetic structures of NdMn 0.1 Fe 0.9 O 3 were determined on the basis of X-ray and neutron powder diffraction experiments as well as from specific heat and magnetization measurements. The compound crystallizes in the orthorhombic crystal structure, space group Pnma, in the entire temperature interval 20 mK < T < 300 K. The lattice parameters exhibit standard thermal expansion effects for T > 20 K and at lower temperatures the anomalies due to magnetostriction effect were observed. The iron sublattice orders magnetically into 3 different magnetic structures, namely into Γ 5 = (A x , F y , G z) for 130 K < T < T N (Néel temperature); Γ 1 = (G x , C y , A z) for 15 K < T < 130 K and Γ 3 = (C x , G y , F z) for 20 mK < T < 15 K. The Nd ions order at temperatures below 1.6–1.75 K into the same Γ 3 phase as the iron sublattice at these temperatures. The obtained magnetic structures fit perfectly in between the magnetic phases of closely related NdFeO 3 and NdMn 0.5 Fe 0.5 O 3 compounds. Our study, together with all previously published data, completes the entire magnetic phase diagram of NdMn 1− x Fe x O 3 (0 ≤ x ≤ 1) solid solution substitutional system. [ABSTRACT FROM AUTHOR]

Organo-metallic compounds Cu( en )(H 2 O) 2 SO 4 ( en =C 2 H 8 N 2 ) and Cu( tn )Cl 2 ( tn =C 3 H 10 N 2 ) representing S =1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/ k B ≈3 K, have been examined by specific heat measurements at temperatures down to nominally 50 mK and magnetic fields up to 14 T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures. A phase transition to long-range order was observed in Cu( en )(H 2 O) 2 SO 4 at T C =0.9 K while hidden in Cu( tn )Cl 2 . A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii–Kosterlitz–Thouless transition theoretically predicted for ideal two-dimensional magnets. [ABSTRACT FROM AUTHOR]