Zero-field muon spin rotation study on genuine organic ferromagnets, 4-arylmethyleneamino-2,2,6,6-tetramethylpiperidin-1-yloxyls (aryl=4-biphenylyl and phenyl)
“…A distinct heat capacity peak due to the ferromagnetic phase transition was observed at T C ) 0.19 K, which coincides well with T C ) 0.18 K by the magnetic susceptibility measurement 10d,10f and T C ) 0.17 K by the µSR measurement. 11 Furthermore, a heat capacity hump was found in the temperature region centered around 1 K. This thermal anomaly can be regarded as a short-range ordering effect of spins characteristic of low-dimensional magnets.…”
Section: Resultsmentioning
confidence: 94%
“…On the basis of the magnetic susceptibilities above T C ,10c the intermolecular exchange interaction parameter was estimated to be J / k B = 0.87 K by the spin quantum number S = 1 / 2 Heisenberg linear chain model and J / k B = 2.2 K by the singlet−triplet model, where k B denotes Boltzmann's constant. Zero-field muon spin rotation/relaxation/resonance (μSR) indicated that BATMP crystal is a three-dimensional Heisenberg ferromagnet below T C = 0.17 K. X-ray structural analysis and theoretical calculation 10d,12 predicted that BATMP crystal would have a two-dimensional ferromagnetic structure parallel to the bc plane. 1 Molecular structure of BATMP and CATMP.…”
Heat capacities of the organic free radical ferromagnet 4-benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (BATMP) crystal were measured in the temperature range between 0.1 and 300 K by adiabatic calorimetry.
A ferromagnetic phase transition was found at T
C = 0.19 K, and a broad heat-capacity anomaly was found
arising from the short-range ordering above T
C characteristic of low-dimensional magnetic spin systems. The
enthalpy and entropy gains due to both the magnetic phase transition and the heat-capacity anomaly were
evaluated to be ΔH = 3.86 J mol-1 and ΔS = 5.64 J K-1 mol-1, respectively. The value of the experimental
magnetic entropy agrees well with the theoretical value R ln 2 (5.76 J K-1 mol-1) expected for a spin quantum
number S = 1/2 spin system (R is the gas constant). The magnetic heat capacity hump due to the short-range
order was well accounted for in terms of an S = 1/2 one-dimensional ferromagnetic Heisenberg model with
the intrachain exchange interaction J/k
B = 0.95 K (k
B is Boltzmann's constant). This fact suggests that BATMP
crystal is a one-dimensional ferromagnet above T
C. The spin wave analysis of the magnetic heat capacities
below T
C revealed that BATMP crystal is in a three-dimensional ferromagnetic state below T
C and the averaged
interchain exchange interaction is J‘/k
B = 0.026 K.
“…A distinct heat capacity peak due to the ferromagnetic phase transition was observed at T C ) 0.19 K, which coincides well with T C ) 0.18 K by the magnetic susceptibility measurement 10d,10f and T C ) 0.17 K by the µSR measurement. 11 Furthermore, a heat capacity hump was found in the temperature region centered around 1 K. This thermal anomaly can be regarded as a short-range ordering effect of spins characteristic of low-dimensional magnets.…”
Section: Resultsmentioning
confidence: 94%
“…On the basis of the magnetic susceptibilities above T C ,10c the intermolecular exchange interaction parameter was estimated to be J / k B = 0.87 K by the spin quantum number S = 1 / 2 Heisenberg linear chain model and J / k B = 2.2 K by the singlet−triplet model, where k B denotes Boltzmann's constant. Zero-field muon spin rotation/relaxation/resonance (μSR) indicated that BATMP crystal is a three-dimensional Heisenberg ferromagnet below T C = 0.17 K. X-ray structural analysis and theoretical calculation 10d,12 predicted that BATMP crystal would have a two-dimensional ferromagnetic structure parallel to the bc plane. 1 Molecular structure of BATMP and CATMP.…”
Heat capacities of the organic free radical ferromagnet 4-benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (BATMP) crystal were measured in the temperature range between 0.1 and 300 K by adiabatic calorimetry.
A ferromagnetic phase transition was found at T
C = 0.19 K, and a broad heat-capacity anomaly was found
arising from the short-range ordering above T
C characteristic of low-dimensional magnetic spin systems. The
enthalpy and entropy gains due to both the magnetic phase transition and the heat-capacity anomaly were
evaluated to be ΔH = 3.86 J mol-1 and ΔS = 5.64 J K-1 mol-1, respectively. The value of the experimental
magnetic entropy agrees well with the theoretical value R ln 2 (5.76 J K-1 mol-1) expected for a spin quantum
number S = 1/2 spin system (R is the gas constant). The magnetic heat capacity hump due to the short-range
order was well accounted for in terms of an S = 1/2 one-dimensional ferromagnetic Heisenberg model with
the intrachain exchange interaction J/k
B = 0.95 K (k
B is Boltzmann's constant). This fact suggests that BATMP
crystal is a one-dimensional ferromagnet above T
C. The spin wave analysis of the magnetic heat capacities
below T
C revealed that BATMP crystal is in a three-dimensional ferromagnetic state below T
C and the averaged
interchain exchange interaction is J‘/k
B = 0.026 K.
“…where n = 4 and ω i , φ i , and λ i are the angular frequency, the initial phase, and the relaxation rate of the i-th muon precession, A tail and λ tail are the asymmetry and the relaxation rate for the "1/3 tail" signal [24,25], as we measured powder samples. The quality of the fit, shown for NVO, is represented by the solid green line in Fig.…”
Section: B Metallic Region; Ncvo With X ≥ 083mentioning
We present muon-spin rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic (AF) zigzag chain compounds, NaxCa1−xV2O4. In this family, we explore the magnetic properties from the metallic NaV2O4 to the insulating CaV2O4. We find a critical xc(∼ 0.833) which separates the low and high Na-concentration dependent transition temperature and its magnetic ground state. In the x < xc compounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the x > xc compounds, multiple sub-phases appear with temperature and x. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.
“…The solid-state physical chemistry of such systems is very rich, showing ferromagnetic [11] or antiferromagnetic properties [12,13,14], magnetic phase transitions [15,16], all of these with mechanisms due to supramolecular effects [17,18,19,20,21,22]. The challenges are higher in the tentative account of magnetic measurements for systems in solution [23], where one might no longer benefit from the knowledge and stability of molecular and supramolecular structures, like in crystals, facing innumerable and transient possibilities of association.…”
Nitroxide-based radicals, having the advantage of firm chemical stability, are usable as probes in the detection of nanoscale details in the chemical environment of various multi-component systems, based on subtle variations in their electron paramagnetic resonance spectra. We propose a systematic walk through the vast area of problems and inquires that are implied by the rationalization of solvent effects on the spectral parameters, by first-principle methods of structural chemistry. Our approach consists of using state-of-the-art procedures, like Density Functional Theory (DFT), on properly designed systems, kept at the border of idealization and chemical realism. Thus, we investigate the case of real solvent molecules intervening in different configurations between two radical molecules, in comparison with radicals taken in vacuum or having the solvent that is treated by surrogate models, such as polarization continuum approximation. In this work, we selected the dichloromethane as solvent and the prototype radicals abbreviated TEMPO ((2,2,6,6-Tetramethylpiperidin-1-yl) oxyl). In another branch of the work, we check the interaction of radicals with large toroidal molecules, β-cyclodextrin, and cucurbit[6]uril, modeling the interaction energy profile at encapsulation. The drawn synoptic view offers valuable rationales for understanding spectroscopy and energetics of nitroxide radicals in various environments, which are specific to soft chemistry.
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