Magnetic and structural studies of the alloy system REIn0.5Ag0.5

The structural and magnetic properties of the alloy system REIn_0.5Ag_0.5 [RE = Gd, Tb, Dy, Ho, Er, Tm and Yb] are reported. All these alloys (except that of Yb) crystallize in a cubic CsCl type structure at room temperature. Low temperature X-ray diffraction data does not reveal any structural phase transformation down to 8 K. On the basis of magnetic susceptibility data at a different temperature (3–300 K) and applied magnetic field (2 × 10⁵ to 8 × 10⁶ A m^-1, it has been concluded that GdIn_0.5Ag_0.5 is ferromagnetic (T_c = 118 K), TbIn_0.5Ag_0.5 and DyIn_0.5Ag_0.5 are meta magnetic (T_N = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (T_N) equal to 24, 22, 21 and 20 K, respectively. The evaluated effective magneton number (p) is found to be slightly larger compared to theoretical values for tripositive ions of Gd, Tb and Dy and a bit smaller for Ho, Er, Tm and Yb. The results have been qualitatively explained using appropriate theories.     

Spin reorientation in Tm2Fe14B

The magnetic structures of Tm₂Fe₁₄B above and below its spin reorientation temperature (approx. 316 K) have been determined from high resolution neutron powder diffraction measurements.Within experimental accuracy all magnetic moments lie in the basal plane at 294 K and along the c-axis at 340 K. The Tm and Fe moments are antiparallel.     

The magnetic structures of HoTiO3 and ErTiO3

The magnetic structures of rare-earth titanium perovskites, ErTiO₃ and HoTiO₃, have been determined at 4.2 K by neutron diffraction. The Er³⁺ moment of (8.5 ± 0.5) μ_B lies along [001] and is colinear with the titanium moment of (-0.7 ± 0.3) μ_B. The Ho³⁺ moment of (8.1 ± 0.5) μ_B is inclined at an angle of 24° to the bc plane and 32° to the ab pla so as to produce an antiferromagnetic ordering of the x component and a ferromagnetic ordering of the y and the z components. The titanium moment of (-0.55 ± 0.3) μ_B lies in the bc plane but its precise direction has not been determined.     

Magnetic properties of TmxDy1−xFeO3 single crystals

The magnetic behaviour of Tm_xDy_1?xFeO₃ (x = 0.3; 0.5; 0.7; 1.0) single crystals in the temperature range 90-4.2° K were investigated. The transition from the weak ferromagnetic to antiferromagnetic state was observed at about 9° K for Tm_0.3Dy_0.7FeO₃ single crystal. The reorientation of weak ferromagnetic moment from c- to a-axis was observed for Tm_0.7Dy_0.3FeO₃ single crystal at 35–65° K. The magnetic structure change of iron and rare-earth ions took place when external magnetic field was applied. The thulium and disprosium ion interaction does not essentially influence on the single crystal magnetic properties of the substituted compounds in a low temperature range.     

Glassy-ferromagnetic behavior in Eu0.5Sr0.5CoO3

Polycrystalline perovskite cobalt oxide Eu_0.5Sr_0.5CoO₃ was prepared by the conventional solid-state reaction method. X-ray powder patterns indicated the prepared samples are pure, cubic perovskite structure (Pm3?m), and with no evidence of any secondary phases. The dc magnetization and ac susceptibility measurements were carried out to investigate the magnetic properties of the sample, and which indicated that cluster-glasses properties are suppressed with the increasing of the coercive field. We denied the possibility of spin-glasses and the existence of the Hopkinson effect in Eu_0.5Sr_0.5CoO₃ through the temperature-dependent ac susceptibility measurements, and explained the magnetic behavior of Eu_0.5Sr_0.5CoO₃ with the competition between magnetic anisotropy and the external magnetic field.     

169Tm Mössbauer effect and magnetic study of Tm6Mn23 and its ternary hydride

The magnetic properties and the lattice constants of Tm₆Mn₂₃ were determined before and after hydrogen absorption. The compound Tm₆Mn₂₃ is ferrimagnetic with an ordering temperature T_c = 404 K. After hydrogen absorption the magnetization is strongly reduced and does not point to the occurrence of magnetic ordering. The strongly increasing hyperfine splitting observed by means of ¹⁶⁹Tm Mössbauer spectroscopy in the hydride for temperature below 60 K, however, shows that the Tm sublattice becomes magnetically ordered after H₂ absorption as well. In uncharged and charged Tm₆Mn₂₃ the values of the Tm moments are close to the free ion values.     

The magnetic structure of U2N2Te

The magnetic structure of tetragonal U₂N₂Te has been studied by means of neutron diffraction on polycrystalline sample. A ferromagnetic alignment of the magnetic moments below 68 K has been confirmed. The best agreement between the calculated and observed intensities of the magnetic reflections has been obtained for the moment direction forming an angle 70 ± 5° to the tetragonal axis. The magnitude of the uranium ordered moment was found to be 2.50 ± 0.05 μ_B.     

相分离Eu0.5Sr0.5MnO3体系中的场诱导磁相变及输运特性研究

研究了半掺杂相分离锰氧化物Eu_0.5Sr_0.5MnO₃样品的结构和电磁输运特性.在半掺杂情况下,该样品呈O′型正交结构,表明样品存在典型的Jahn-Teller畸变;在75 K附近样品的顺磁/反铁磁背景中开始出现铁磁相,在更低的温度42 K,4000 A/m磁场下M-T的场冷曲线和零场冷曲线出现明显分岔,样品的交流磁化率实部随温度的变化曲线中也在42 K观察到尖峰的出现,表现出团簇玻璃行为.在无外加磁场下该样品在 关键词： 多相竞争 半掺杂 铁磁团簇     

Magnetic structures of dysprosium oxysulfide and dysprosium oxyselenide

The magnetic structures of Dy₂O₂S and Dy₂O₂Se have been determined by neutron diffraction experiments at 1.5 K. For these two antiferromagnetic compounds the magnetic unit cell is orthohexagonal and doubled along the c-axis. The antiferromagnetic direction is parallel to the c-axis; the values of the Dy³⁺ magnetic moment in Dy₂O₂S and Dy₂O₂Se are 7.2±0.5 μ_B and 9.0±0.5 μ_B, respectively.     

The antiferromagnetic structure of TbB4

The magnetic structure of the rare earth tetraboride TbB₄ (crystallographic space group P4/mbm) has been determined by neutron diffraction on a polycrystalline sample. Below the experimentally determined Néel temperature of T_N = (43±1) K TbB₄ is ordered antiferromagnetically. The data refinement yielded a magnetic moment value of (7.7 ± 0.2) μ_B/Tb ion at 4.2 K which we interpret as Tb⁴⁺. The magnetic structure is antiferromagnetic collinear with the moments perpendicular to the tetragonal axis.     

Phonon mode softening at the ferroelectric transition in Eu0.5Ba0.5TiO3

We have observed the effects of phonon mode softening at the ferroelectric transition in Eu_0.5Ba_0.5TiO₃ by ¹⁵¹Eu Mössbauer spectroscopy. Both Eu²⁺ and Eu³⁺ spectral components are observed in the relative area ratio of 90% : 10% and both show a decrease in subspectral area at the transition, centred at 175 K, due to phonon mode softening. Surprisingly, the temperature dependence of the f-factor shows a much stronger response in the Eu³⁺ component than in the Eu²⁺ one. Preliminary analysis of neutron powder diffraction data rules out the possibility that some of the europium might be located on titanium sites.     

Magnetic structure of the cubic U2Te3 with a non-stoichiometric Th3P4 type of structure

The neutron diffraction patterns of the cubic U₂Te₃ have been obtained at 15 and 150 K. There are no extrapeaks of magnetic origin below the Curie point T_c = 70 ± 5 K. Thus the ordering corresponds to a collinear ferromagnetic structure. The value of the magnetic moment is 1.78 μ_B which is close to those values determined for a few cubic uranium pnictides and chalcogenides.     

Neutronenbeugungsuntersuchungen der magnetischen Struktur von TmCo3

The magnetic structure of the intermetallic TmCo₃ compound, determined by neutron diffraction measurements at 4.2 K on a powder sample, is colinear to the hexagonal c-axis, with the magnetic moments of Tm- and Co-ions being antiparallel coupled. The saturation moments have been found to beµ(Tm)=6.5µ _B andµ(Co)=0.8µ _B . The calculated magnetic moment of the Tm-ion by crystal field theory, based on a point charge model, is that of the free Tm³⁺ ion.     

Influence of Ni-concentration on the magnetic structure in Tb(Cu,Ni)2 system

A powder sample of orthorhombic Tb(Cu_0.7Ni_0.3)₂ has been studied by neutron diffraction at T = 4.2 K and above the Curie temperature. It is found that this compound is ferromagnetically ordered at 4.2 K. The magnetic moment of Tb in this compound is (9.2 ± 0.2)μ_B, with components (2.2 ± 0.2, 0, 8.9 ± 0.1)μ_B. The influence of the Ni-concentration on the magnetic structure is discussed in the whole Tb(Cu, Ni)₂ system.     

The spin wave dispersion relation of disordered Pd0.5Fe0.5

The spin wave spectrum of chemically disordered Pd_0.5Fe_0.5 has been determined by neutron inelastic scattering. At small wavevectors, the dispersion curve is quadratic and isotropic with a spin wave stiffness constant of 47.9 ± 3.3 THz Ų, at room temperature. There is little sign of the anisotropic behaviour observed in the ordered alloy Pd₃Fe.     

Thermoluminescence of rare earth activated CdSO4, SrSO4 and BaSO4

The thermoluminescence (TL) of rare earth (RE) activated sulfates of Cd, Sr and Ba was studied above room temperature. Many of the phosphors prepared exhibit an extremely bright TL following X-irradiation (most notably with Sm, Eu, Tb, Dy and Tm dopants), having an efficiency comparable to that of the highest sensitivity phosphors available for TL dosimetry, and exhibiting activator-induced glow peaks between 405 and 480°K. In a given lattice, the RE³⁺ ions produce a characteristic glow peak at the same temperature (independent of the particular RE ion), whereas Eu²⁺ produces a single glow peak at a different temperature. A decrease in glow peak temperature with increasing interatomic spacing was observed in the homologous SrSO₄-BaSO₄ system - this shift being most pronounced in the Eu²⁺ -doped materials. TL emission spectra were obtained for trivalent Sm, Tb, Dy and Tm and for divalent Eu in these sulfates (and also in CaSO₄).     

Magnetic structures of the rare earth orthotitanites RTiO3; R = Tb,Dy, Tm and Yb

The magnetic structures of the rare earth orthotitanites, RTiO₃, R = Tb, Dy, Tm and Yb, have been solved using neutron powder diffraction techniques.Two different types of magnetic structure have been found. One has the titanium and rare earth moments antiparallel along the c axis. The other structure has the rare earth moments in the ab plane with both ferromagnetic and antiferromagnetic components. In TbTiO₃, the terbium moment of (8.1 ± 0.4)μ_β has ferromagnetic and antiferromagnetic components along the [100] and [010] directions, respectively, with the moments lying at an angle of (36 ± 3)° to the [100] direction. In DyTiO₃, the dysprosium moment of (9.7 ± 0.7)μ_β has ferromagnetic and antiferromagnetic components along the [010] and [100] directions, respectively, with the moments making an angle of (31 ± 5)° to the [010] direction. TmTiO₃ has a thulium moment of (6.0 ± 0.4)μ_β in a ferromagnetic array along the [001] direction. The average titanium moment in the orthotitanites is (0.7 ± 0.3)μ_β in a direction antiparallel to the ferromagnetic component of the rare earth moment. The ytterbium moment in YbTiO₃ is quenched. It is found to be (1.7 ± 0.2)μ_β assuming a moment direction along [001]. The rare earth moment directions are found to be remarkably consistent in the series RMO₃, M = Ti, Cr, Fe and Al.     

Magnetic structures and magnetic susceptibilities of terbium oxysulfide and oxyselenide

For the two isomorphous compounds Tb₂O₂S and Tb₂O₂Se, the magnetic susceptibility measurements on powder samples show an antiferromagnetic ordering with Néel temperatures of about 7.7 and 7K respectively. Differing in this respect from the other rare earth oxyselenides, the magnetic anisotropy of Tb₂O₂Se at low temperature is weaker than that of Tb₂O₂S.We also determine the magnetic structures of these two compounds by neutron diffraction experiments at 1.5K. The magnetic cell is orthohexagonal and doubled along the c-axis; the magnetic moments make an angle, with the c-axis, of 47 ± 10° for Tb₂O₂S and 30 ± 10° for Tb₂O₂Se and the moment values at 1.5K are 8.14 ± 0.2μ_B and 6.5 ± 0.2μ_B, respectively.It is rather exceptional that in a rare earth uniaxial compound the magnetic moment makes an angle with the c-axis. However we interpret this situation by the fact that several levels exist very near to the ground state. The crystal field calculations are in good agreement with the experimental results.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

NMR hyperfine spectrum of 143Nd in ferromagnetic cubic intermetallic NdAl2

The hyperfine spectrum of ¹⁴³Nd in NdAl₂ measured at T = 1.4 K provides values of ∣a_t∣ = 786 ± 0.5 MHz and ∣P_t∣ = 3.25 ± 0.03 MHz. The latter value is in agreement with the expected calculated value obtained from the 4f ground state wave function in a crystal field plus molecular field model, which may be deduced from inelastic neutron scattering experiments combined with susceptibility measurements, or from polarized neutron diffraction experiments. It is shown that the 4f electronic moment can be directly obtained from zero field NMR with good accuracy.