ABSTRACT In this article, we have introduced catalytic application of copper ferrite nanoparticle... more ABSTRACT In this article, we have introduced catalytic application of copper ferrite nanoparticles (CuFe2O4) for one-pot odorless production of aryl alkyl thioethers using thiourea and alkyl bromides in wet polyethylene glycol as a green solvent. The catalyst was also successfully applied for one-pot synthesis of symmetrical diaryl trithiocarbonates via the reaction of sodium sulfide, carbon disulfide and aryl iodides under heterogeneous reaction condition. Magnetic copper ferrite nanoparticles were synthesized using iron (III) chloride and copper (II) chloride, and characterized using XRD, Fr-IR, AAS, and TEM analysis. The catalyst was recycled using simple magnetic separation and reused for the five consecutive runs in the reaction of iodobenzene, thiourea and benzyl bromide without appreciable loss of activity.
We find that in the ferromagnetic semiconductor EuS, near its Curie temperature, a single band ed... more We find that in the ferromagnetic semiconductor EuS, near its Curie temperature, a single band edge photon generates a spin polaron (SP), whose magnetic moment approaches 20 000 Bohr magnetons. This is much larger than the supergiant photoinduced SPs in antiferromagnetic europium chalcogenides, reported previously. The larger SP in ferromagnetic EuS, and still larger expected for EuO, is explained by a larger Bohr radius of the photoexcited electron state, which encircles and polarizes a greater number of lattice spins. However, because the wave function of the photoexcited electron spreads over a greater volume, the photoexcited electron's exchange interaction with individual lattice spins weakens, which makes the SP more easily quenched thermally.
Polymeric particles loaded with biocompatible magnetic nanoparticles are promising platforms to p... more Polymeric particles loaded with biocompatible magnetic nanoparticles are promising platforms to perform therapy and diagnostic of diseases, acting as the so called theranostic agents. In this work, magnetite nanoparticles were synthesized by coprecipitation method and encapsulated with Polycaprolactone (PCL) and Poloxamer 188 polymers through the innovative Nano Spray Drying technique. X-Ray Diffraction and Infrared Spectroscopy confirmed that the formed particles are composed by PCL, Poloxamer and magnetite, with amount of magnetite determined as 3% by Thermogravimetric Analysis. Particles present a superparamagnetic-like behaviour at 300 K, having negligible coercivity. Dynamic Light Scattering and Scanning Electron Microscopy indicated that the hydrodynamic diameters are of 49 nm for magnetite nanoparticles and of approximately 600 nm for encapsulated particles, with aspect analogous to a "nanocookie" of a PCL/Poloxamer blend with magnetite nanoparticles embedded in it. Cytotoxicity assays presented IC 50 superior to 2.5 mg/mL for healthy cells and a higher viability of cancer cells in comparison to control, suggesting that the particles may have affinity for tumours, which can be useful for the intended biological applications.
We demonstrate that light resonant with the bandgap forces the antiferromagnetic semiconducor EuS... more We demonstrate that light resonant with the bandgap forces the antiferromagnetic semiconducor EuSe to enter ferromagnetic alignment in the picosecond time scale. A photon generates an electronhole pair, whose electron forms a supergiant spin polaron of magnetic moment of nearly 6,000 Bohr magnetons. By increasing the light intensity, the whole of the sample can be fully magnetized. The key to the novel large photoinduced magnetization mechanism is the huge enhancement of the magnetic susceptibility when both antiferromagnetic and ferromagnetic interactions are present in the material, and are of nearly equal magnitude, as is the case in EuSe.
Abstract Polycrystalline NiMn2O4 samples were synthesized by sol-gel method at 500 °C (S500), 700... more Abstract Polycrystalline NiMn2O4 samples were synthesized by sol-gel method at 500 °C (S500), 700 °C (S700), and 800 °C (S800). The three samples were then structurally characterized by X-ray diffraction and Rietveld refinement. Results indicate that samples are single phase and crystallize in the Fd 3 ¯ m space group with spinel structure. Williamson-Hall analysis shows that samples present different lattice strains. NiMn2O4 compounds show the magnetic transition from ferrimagnetic to paramagnetic at nearly 100 K. Hysteresis loops measured at T = 1.7 K after cooling the samples under magnetic field are asymmetric along the field axis.
Three new distant neighbor (DN) antiferromagnetic exchange constants have been measured in wurtzi... more Three new distant neighbor (DN) antiferromagnetic exchange constants have been measured in wurtzite Cd1–xMnxS (x = 0.0087 and x = 0.0278) using the magnetization steps method in the millikelvin regime. The second (J(2)), third (J(3)), and fourth (J(4)) largest exchange constants (after the two first neighbor exchange interactions J1 and J1′) have been measured. The results are J(2) = 300 ± 10 mK, J(3) = 173 ± 10 mK, and J(4) = 55 ± 10 mK. No significant change of the exchange constant values has been observed as a function of the Mn concentration. The mapping of the DN exchange interactions has been investigated within a sphere of radius 2 times the nearest neighbors distance. The only way to identify the J constants was using the number coordination Zn of the different DN classes: J(2) is associated to DN classes with Zn = 6, J(3) with Zn = 12, and J(4) is ascribed to a group of three DN classes with J values around J(4). The magnitude of the J constants is not in agreement with theoretical predictions o...
The present study reports the successful synthesis of Sn1–xCrxO2 nanoparticles with doping conten... more The present study reports the successful synthesis of Sn1–xCrxO2 nanoparticles with doping content (x) ranging from 0 to 0.20. Samples were synthesized by a polymer precursor method using SnCl2·H2O and Cr(NO3)3·5H2O as metal ion suppliers. In all samples X-ray diffraction data show one single-phase formation (rutile-type), with crystalline size (crystal strain) decreasing (increasing) monotonically while increasing the x content, which are assigned to substitutional solution of Cr and Sn ions in the crystalline structure. In addition to a weak magnetic ordering observed in a few samples (x = 0.01, 0.02, 0.03, and 0.05), paramagnetism is the main magnetic contribution in all synthesized samples, which is due to the presence of two chromium ions (Cr3+ and Cr4+). X-ray photoelectron spectroscopy measurements confirm the coexistence of Cr3+ and Cr4+ ions in excellent agreement with the monotonic decrease of the [Cr3+]/[Cr4+] versus doping content (x), assessed from the fitting of the susceptibility versus tem...
We performed magnetoresistance measurements on Bi2Te3 thin film in the temperature range of T = 1... more We performed magnetoresistance measurements on Bi2Te3 thin film in the temperature range of T = 1.2–4.0 K and for magnetic fields up to 2 T. The curves exhibited anomalous behavior for temperatures below 4.0 K. Different temperature intervals revealed electrical transport through different conductive channels with clear signatures of weak antilocalization. The magnetoresistance curves were explained using the Hikami–Larkin–Nagaoka model and the 2D Dirac modified model. The comparison between the parameters obtained from the two models revealed the transport via topological surface states and bulk states. In addition, a superconductive like transition is observed for the lowest temperatures and we suggest that this effect can be originated from the misfit dislocations caused by strain, giving rise to a superconductive channel between the interface of the film and the substrate.
In this article, we report on structural and magnetic properties of cubic GaN epitaxial layers im... more In this article, we report on structural and magnetic properties of cubic GaN epitaxial layers implanted with Fe ions and subsequently subjected to thermal annealing. The epitaxial quality of the layers was studied by X-ray diffraction rocking curves (x-scans) and Raman spectroscopy. The results show that the implantation damages the crystal structure producing an expansion of the lattice parameter in the implanted region. These damages are partially removed by the thermal treatment. Room temperature ferromagnetism is observed for the sample implanted with a dose of 1.2 Â 10 16 cm À2 , while samples implanted with 2.4 Â 10 16 cm À2 show a coexistence of ferromagnetism and paramagnetism due to disperse Fe 3þ . Thermal annealing changes these magnetic properties. For the low dose sample, the ferromagnetism is converted into paramagnetism while for the high dose we observed an enhancement of the ferromagnetic contribution characterized by a superparamagnetism behavior attributed to Fe-based particles. Published by AIP Publishing.
... SA Nemov, TA Gavrikova, VA Zykov, PA Osipov, and VI Proshin, Semiconductors 32, 689 (1998) [S... more ... SA Nemov, TA Gavrikova, VA Zykov, PA Osipov, and VI Proshin, Semiconductors 32, 689 (1998) [SPIN]. O. Nugraha, W. Tamura, O. Itoh, T. Amemiya, K. Suto, and J. Nishizawa, J. Cryst. ... GT Alekseeva, MV Vedernikov, EA Gurieva, PP Konstantinov, LV Prokof'eva, and Yu. ...
Magnetization steps (MST's) from Mn 2+ pairs in several single crystals of Zn1−xMnxO (0.0056≤x≤0.... more Magnetization steps (MST's) from Mn 2+ pairs in several single crystals of Zn1−xMnxO (0.0056≤x≤0.030), and in one powder (x=0.029), were observed. They were used to determine the four largest exchange constants (largest J's), and the single-ion axial anisotropy parameter, D. The largest two exchange constants, J1/kB=−18.2±0.5 K and J ′ 1 /kB=−24.3±0.6 K, were obtained from large peaks in the differential susceptibility, dM/dH, measured in pulsed magnetic fields, H, up to 500 kOe. These two largest J's are associated with the two inequivalent classes of nearest neighbors (NN's) in the wurtzite structure. The 29% difference between J1 and J ′ 1 is substantially larger than 13% in Cd1−xMnxS, and 15% in Cd1−xMnxSe. The pulsed-field data also indicate that, despite the direct contact between the samples and a superfluid-helium bath, substantial departures from thermal equilibrium occurred during the 7.4 ms pulse. The third-and fourth-largest J's were determined from the magnetization M at 20 mK, measured in dc magnetic fields H up to 90 kOe. Both field orientations H c and H [1010] were studied. (The [1010] direction is perpendicular to the c-axis, [0001].) By definition, neighbors which are not NN's are distant neighbors (DN's). The largest DN exchange constant (third-largest overall), has the value J/kB=−0.543±0.005 K, and is associated with the DN at r=c. Because this is not the closest DN, this result implies that the J's do not decrease monotonically with the distance r. The second-largest DN exchange constant (fourth-largest overall), has the value J/kB≈−0.080 K. It is associated with one of the two classes of neighbors that have a coordination number zn=12, but the evidence is insufficient for a definite unique choice. The dependence of M on the direction of H gives D/kB=−0.039±0.008 K, in fair agreement with −0.031 K from earlier EPR work.
The magnetization M of (CH3NH3)2MnxCd1-xCl4 , with x from 0.025 up to 0.265, was measured at 0.6 ... more The magnetization M of (CH3NH3)2MnxCd1-xCl4 , with x from 0.025 up to 0.265, was measured at 0.6 K in a slowly varying magnetic field B up to 17 T. The exchange interaction in these strongly diluted planar magnetic materials is antiferromagnetic. The in-plane cation structure is well approximated by a square lattice. The observed qualitative features, listed in the order
The magnetization of Pb \V Ce V Se single crystals (x"0.75% and 3.5%) was measured at 20 mK. For ... more The magnetization of Pb \V Ce V Se single crystals (x"0.75% and 3.5%) was measured at 20 mK. For H "" 11 1 12 two magnetization steps were observed at H "5.7$0.2 and H "9.5$0.2 kOe, which are attributed to two kinds of antiferromagnetic Ce>-pairs. For H along 10 0 12 and 11 0 12, the "rst step does not change, indicating that the associated exchange interaction is isotropic (J"!0.26$0.01 K). The second step, on the other hand, is split, possibly due to exchange anisotropy (with an average constant JM "!0.43$0.02 K). These two J's correspond, probably, to nearest-and next-nearest neighbor pairs. The analyses of the sizes of the steps, however, indicate that the distribution of Ce> in the samples studied may be non-random.
Magnetization measurements performed at very low temperatures on three samples of Sn 1Àx Gd x Te;... more Magnetization measurements performed at very low temperatures on three samples of Sn 1Àx Gd x Te; showed that Gdpairs with an exchange constant J ¼ À0:38 K were present in all three samples. In one of the samples, however, another kind of Gd-pairs, with J 0 ¼ À1:3 K was also present. The coexistence of these two ''exchange constants'' in a sample seems to contradict a recent interpretation for the exchange mechanisms in this material.
ramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetr... more ramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN) crystallize as solid solutions (alloys) across a wide range of binary compositions. (F4BImNN) x (BImNN) (1−x) with x < 0.8 gives orthorhombic unit cells, while x ≥ 0.9 gives monoclinic unit cells. In all crystalline samples, the dominant intermolecular packing is controlled by one-dimensional (1D) hydrogen-bonded chains that lead to quasi-1D ferromagnetic behavior. Magnetic analysis over 0.4−300 K indicates ordering with strong 1D ferromagnetic exchange along the chains (J/k = 12−22 K). Interchain exchange is estimated to be 33-to 150-fold weaker, based on antiferromagnetic ordered phase formation below Neél temperatures in the 0.4−1.2 K range for the various compositions. The ordering temperatures of the orthorhombic samples increase linearly as (1 − x) increases from 0.25 to 1.00. The variation is attributed to increased interchain distance corresponding to decreased interchain exchange, when more F4BImNN is added into the orthorhombic lattice. The monoclinic samples are not part of the same trend, due to the different interchain arrangement associated with the phase change.
The magnetization of Sn1-x Eux Te, with x = 0.011 and 0.042, was measured at 20 mK in magnetic fi... more The magnetization of Sn1-x Eux Te, with x = 0.011 and 0.042, was measured at 20 mK in magnetic fields up to 90 kOe. Magnetization steps (MSTs) from pairs and triplets were observed. The MSTs give J /kB = -0.311+/-0.006 K for the dominant Eu-Eu exchange constant. Comparisons of the magnetization curves with numerical simulations indicate that, instead of being
The magnetization of Pb \V Ce V S single crystals was measured at 20 mK and magnetic "eld upto 90... more The magnetization of Pb \V Ce V S single crystals was measured at 20 mK and magnetic "eld upto 90 kOe. Magnetization steps from two types of pairs were observed. The "rst has an isotropic exchange interaction with J"!0.32 K. The second type of pairs gives a structured step which can be explained by an anisotropic exchange interaction. Cluster statistics suggests that both types are nearest-neighbor pairs.
ABSTRACT In this article, we have introduced catalytic application of copper ferrite nanoparticle... more ABSTRACT In this article, we have introduced catalytic application of copper ferrite nanoparticles (CuFe2O4) for one-pot odorless production of aryl alkyl thioethers using thiourea and alkyl bromides in wet polyethylene glycol as a green solvent. The catalyst was also successfully applied for one-pot synthesis of symmetrical diaryl trithiocarbonates via the reaction of sodium sulfide, carbon disulfide and aryl iodides under heterogeneous reaction condition. Magnetic copper ferrite nanoparticles were synthesized using iron (III) chloride and copper (II) chloride, and characterized using XRD, Fr-IR, AAS, and TEM analysis. The catalyst was recycled using simple magnetic separation and reused for the five consecutive runs in the reaction of iodobenzene, thiourea and benzyl bromide without appreciable loss of activity.
We find that in the ferromagnetic semiconductor EuS, near its Curie temperature, a single band ed... more We find that in the ferromagnetic semiconductor EuS, near its Curie temperature, a single band edge photon generates a spin polaron (SP), whose magnetic moment approaches 20 000 Bohr magnetons. This is much larger than the supergiant photoinduced SPs in antiferromagnetic europium chalcogenides, reported previously. The larger SP in ferromagnetic EuS, and still larger expected for EuO, is explained by a larger Bohr radius of the photoexcited electron state, which encircles and polarizes a greater number of lattice spins. However, because the wave function of the photoexcited electron spreads over a greater volume, the photoexcited electron's exchange interaction with individual lattice spins weakens, which makes the SP more easily quenched thermally.
Polymeric particles loaded with biocompatible magnetic nanoparticles are promising platforms to p... more Polymeric particles loaded with biocompatible magnetic nanoparticles are promising platforms to perform therapy and diagnostic of diseases, acting as the so called theranostic agents. In this work, magnetite nanoparticles were synthesized by coprecipitation method and encapsulated with Polycaprolactone (PCL) and Poloxamer 188 polymers through the innovative Nano Spray Drying technique. X-Ray Diffraction and Infrared Spectroscopy confirmed that the formed particles are composed by PCL, Poloxamer and magnetite, with amount of magnetite determined as 3% by Thermogravimetric Analysis. Particles present a superparamagnetic-like behaviour at 300 K, having negligible coercivity. Dynamic Light Scattering and Scanning Electron Microscopy indicated that the hydrodynamic diameters are of 49 nm for magnetite nanoparticles and of approximately 600 nm for encapsulated particles, with aspect analogous to a "nanocookie" of a PCL/Poloxamer blend with magnetite nanoparticles embedded in it. Cytotoxicity assays presented IC 50 superior to 2.5 mg/mL for healthy cells and a higher viability of cancer cells in comparison to control, suggesting that the particles may have affinity for tumours, which can be useful for the intended biological applications.
We demonstrate that light resonant with the bandgap forces the antiferromagnetic semiconducor EuS... more We demonstrate that light resonant with the bandgap forces the antiferromagnetic semiconducor EuSe to enter ferromagnetic alignment in the picosecond time scale. A photon generates an electronhole pair, whose electron forms a supergiant spin polaron of magnetic moment of nearly 6,000 Bohr magnetons. By increasing the light intensity, the whole of the sample can be fully magnetized. The key to the novel large photoinduced magnetization mechanism is the huge enhancement of the magnetic susceptibility when both antiferromagnetic and ferromagnetic interactions are present in the material, and are of nearly equal magnitude, as is the case in EuSe.
Abstract Polycrystalline NiMn2O4 samples were synthesized by sol-gel method at 500 °C (S500), 700... more Abstract Polycrystalline NiMn2O4 samples were synthesized by sol-gel method at 500 °C (S500), 700 °C (S700), and 800 °C (S800). The three samples were then structurally characterized by X-ray diffraction and Rietveld refinement. Results indicate that samples are single phase and crystallize in the Fd 3 ¯ m space group with spinel structure. Williamson-Hall analysis shows that samples present different lattice strains. NiMn2O4 compounds show the magnetic transition from ferrimagnetic to paramagnetic at nearly 100 K. Hysteresis loops measured at T = 1.7 K after cooling the samples under magnetic field are asymmetric along the field axis.
Three new distant neighbor (DN) antiferromagnetic exchange constants have been measured in wurtzi... more Three new distant neighbor (DN) antiferromagnetic exchange constants have been measured in wurtzite Cd1–xMnxS (x = 0.0087 and x = 0.0278) using the magnetization steps method in the millikelvin regime. The second (J(2)), third (J(3)), and fourth (J(4)) largest exchange constants (after the two first neighbor exchange interactions J1 and J1′) have been measured. The results are J(2) = 300 ± 10 mK, J(3) = 173 ± 10 mK, and J(4) = 55 ± 10 mK. No significant change of the exchange constant values has been observed as a function of the Mn concentration. The mapping of the DN exchange interactions has been investigated within a sphere of radius 2 times the nearest neighbors distance. The only way to identify the J constants was using the number coordination Zn of the different DN classes: J(2) is associated to DN classes with Zn = 6, J(3) with Zn = 12, and J(4) is ascribed to a group of three DN classes with J values around J(4). The magnitude of the J constants is not in agreement with theoretical predictions o...
The present study reports the successful synthesis of Sn1–xCrxO2 nanoparticles with doping conten... more The present study reports the successful synthesis of Sn1–xCrxO2 nanoparticles with doping content (x) ranging from 0 to 0.20. Samples were synthesized by a polymer precursor method using SnCl2·H2O and Cr(NO3)3·5H2O as metal ion suppliers. In all samples X-ray diffraction data show one single-phase formation (rutile-type), with crystalline size (crystal strain) decreasing (increasing) monotonically while increasing the x content, which are assigned to substitutional solution of Cr and Sn ions in the crystalline structure. In addition to a weak magnetic ordering observed in a few samples (x = 0.01, 0.02, 0.03, and 0.05), paramagnetism is the main magnetic contribution in all synthesized samples, which is due to the presence of two chromium ions (Cr3+ and Cr4+). X-ray photoelectron spectroscopy measurements confirm the coexistence of Cr3+ and Cr4+ ions in excellent agreement with the monotonic decrease of the [Cr3+]/[Cr4+] versus doping content (x), assessed from the fitting of the susceptibility versus tem...
We performed magnetoresistance measurements on Bi2Te3 thin film in the temperature range of T = 1... more We performed magnetoresistance measurements on Bi2Te3 thin film in the temperature range of T = 1.2–4.0 K and for magnetic fields up to 2 T. The curves exhibited anomalous behavior for temperatures below 4.0 K. Different temperature intervals revealed electrical transport through different conductive channels with clear signatures of weak antilocalization. The magnetoresistance curves were explained using the Hikami–Larkin–Nagaoka model and the 2D Dirac modified model. The comparison between the parameters obtained from the two models revealed the transport via topological surface states and bulk states. In addition, a superconductive like transition is observed for the lowest temperatures and we suggest that this effect can be originated from the misfit dislocations caused by strain, giving rise to a superconductive channel between the interface of the film and the substrate.
In this article, we report on structural and magnetic properties of cubic GaN epitaxial layers im... more In this article, we report on structural and magnetic properties of cubic GaN epitaxial layers implanted with Fe ions and subsequently subjected to thermal annealing. The epitaxial quality of the layers was studied by X-ray diffraction rocking curves (x-scans) and Raman spectroscopy. The results show that the implantation damages the crystal structure producing an expansion of the lattice parameter in the implanted region. These damages are partially removed by the thermal treatment. Room temperature ferromagnetism is observed for the sample implanted with a dose of 1.2 Â 10 16 cm À2 , while samples implanted with 2.4 Â 10 16 cm À2 show a coexistence of ferromagnetism and paramagnetism due to disperse Fe 3þ . Thermal annealing changes these magnetic properties. For the low dose sample, the ferromagnetism is converted into paramagnetism while for the high dose we observed an enhancement of the ferromagnetic contribution characterized by a superparamagnetism behavior attributed to Fe-based particles. Published by AIP Publishing.
... SA Nemov, TA Gavrikova, VA Zykov, PA Osipov, and VI Proshin, Semiconductors 32, 689 (1998) [S... more ... SA Nemov, TA Gavrikova, VA Zykov, PA Osipov, and VI Proshin, Semiconductors 32, 689 (1998) [SPIN]. O. Nugraha, W. Tamura, O. Itoh, T. Amemiya, K. Suto, and J. Nishizawa, J. Cryst. ... GT Alekseeva, MV Vedernikov, EA Gurieva, PP Konstantinov, LV Prokof&amp;amp;#x27;eva, and Yu. ...
Magnetization steps (MST's) from Mn 2+ pairs in several single crystals of Zn1−xMnxO (0.0056≤x≤0.... more Magnetization steps (MST's) from Mn 2+ pairs in several single crystals of Zn1−xMnxO (0.0056≤x≤0.030), and in one powder (x=0.029), were observed. They were used to determine the four largest exchange constants (largest J's), and the single-ion axial anisotropy parameter, D. The largest two exchange constants, J1/kB=−18.2±0.5 K and J ′ 1 /kB=−24.3±0.6 K, were obtained from large peaks in the differential susceptibility, dM/dH, measured in pulsed magnetic fields, H, up to 500 kOe. These two largest J's are associated with the two inequivalent classes of nearest neighbors (NN's) in the wurtzite structure. The 29% difference between J1 and J ′ 1 is substantially larger than 13% in Cd1−xMnxS, and 15% in Cd1−xMnxSe. The pulsed-field data also indicate that, despite the direct contact between the samples and a superfluid-helium bath, substantial departures from thermal equilibrium occurred during the 7.4 ms pulse. The third-and fourth-largest J's were determined from the magnetization M at 20 mK, measured in dc magnetic fields H up to 90 kOe. Both field orientations H c and H [1010] were studied. (The [1010] direction is perpendicular to the c-axis, [0001].) By definition, neighbors which are not NN's are distant neighbors (DN's). The largest DN exchange constant (third-largest overall), has the value J/kB=−0.543±0.005 K, and is associated with the DN at r=c. Because this is not the closest DN, this result implies that the J's do not decrease monotonically with the distance r. The second-largest DN exchange constant (fourth-largest overall), has the value J/kB≈−0.080 K. It is associated with one of the two classes of neighbors that have a coordination number zn=12, but the evidence is insufficient for a definite unique choice. The dependence of M on the direction of H gives D/kB=−0.039±0.008 K, in fair agreement with −0.031 K from earlier EPR work.
The magnetization M of (CH3NH3)2MnxCd1-xCl4 , with x from 0.025 up to 0.265, was measured at 0.6 ... more The magnetization M of (CH3NH3)2MnxCd1-xCl4 , with x from 0.025 up to 0.265, was measured at 0.6 K in a slowly varying magnetic field B up to 17 T. The exchange interaction in these strongly diluted planar magnetic materials is antiferromagnetic. The in-plane cation structure is well approximated by a square lattice. The observed qualitative features, listed in the order
The magnetization of Pb \V Ce V Se single crystals (x"0.75% and 3.5%) was measured at 20 mK. For ... more The magnetization of Pb \V Ce V Se single crystals (x"0.75% and 3.5%) was measured at 20 mK. For H "" 11 1 12 two magnetization steps were observed at H "5.7$0.2 and H "9.5$0.2 kOe, which are attributed to two kinds of antiferromagnetic Ce>-pairs. For H along 10 0 12 and 11 0 12, the "rst step does not change, indicating that the associated exchange interaction is isotropic (J"!0.26$0.01 K). The second step, on the other hand, is split, possibly due to exchange anisotropy (with an average constant JM "!0.43$0.02 K). These two J's correspond, probably, to nearest-and next-nearest neighbor pairs. The analyses of the sizes of the steps, however, indicate that the distribution of Ce> in the samples studied may be non-random.
Magnetization measurements performed at very low temperatures on three samples of Sn 1Àx Gd x Te;... more Magnetization measurements performed at very low temperatures on three samples of Sn 1Àx Gd x Te; showed that Gdpairs with an exchange constant J ¼ À0:38 K were present in all three samples. In one of the samples, however, another kind of Gd-pairs, with J 0 ¼ À1:3 K was also present. The coexistence of these two ''exchange constants'' in a sample seems to contradict a recent interpretation for the exchange mechanisms in this material.
ramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetr... more ramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN) crystallize as solid solutions (alloys) across a wide range of binary compositions. (F4BImNN) x (BImNN) (1−x) with x < 0.8 gives orthorhombic unit cells, while x ≥ 0.9 gives monoclinic unit cells. In all crystalline samples, the dominant intermolecular packing is controlled by one-dimensional (1D) hydrogen-bonded chains that lead to quasi-1D ferromagnetic behavior. Magnetic analysis over 0.4−300 K indicates ordering with strong 1D ferromagnetic exchange along the chains (J/k = 12−22 K). Interchain exchange is estimated to be 33-to 150-fold weaker, based on antiferromagnetic ordered phase formation below Neél temperatures in the 0.4−1.2 K range for the various compositions. The ordering temperatures of the orthorhombic samples increase linearly as (1 − x) increases from 0.25 to 1.00. The variation is attributed to increased interchain distance corresponding to decreased interchain exchange, when more F4BImNN is added into the orthorhombic lattice. The monoclinic samples are not part of the same trend, due to the different interchain arrangement associated with the phase change.
The magnetization of Sn1-x Eux Te, with x = 0.011 and 0.042, was measured at 20 mK in magnetic fi... more The magnetization of Sn1-x Eux Te, with x = 0.011 and 0.042, was measured at 20 mK in magnetic fields up to 90 kOe. Magnetization steps (MSTs) from pairs and triplets were observed. The MSTs give J /kB = -0.311+/-0.006 K for the dominant Eu-Eu exchange constant. Comparisons of the magnetization curves with numerical simulations indicate that, instead of being
The magnetization of Pb \V Ce V S single crystals was measured at 20 mK and magnetic "eld upto 90... more The magnetization of Pb \V Ce V S single crystals was measured at 20 mK and magnetic "eld upto 90 kOe. Magnetization steps from two types of pairs were observed. The "rst has an isotropic exchange interaction with J"!0.32 K. The second type of pairs gives a structured step which can be explained by an anisotropic exchange interaction. Cluster statistics suggests that both types are nearest-neighbor pairs.
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