Phase Diagram Of Spin-1 Research Articles

Mössbauer and Magnetometric Studies of Spin Reorientations in Er2-xThxFe14B

The Er2ixThxFe14B (x = 0:5, 1.0, 1.5) polycrystalline compounds have been investigated with 57 Fe Mossbauer spectroscopy in the 50{330 K tem- perature range and magnetometry in the temperature range of 4.2{340 K. Initial magnetization vs. temperature measurements allowed us to establish the temperature regions of reorientations and also the Curie temperatures of the compounds. The spin reorientation phenomena (changes from pla- nar to axial spin arrangements) have been studied extensively by a narrow step temperature Mossbauer scanning in the vicinity of the spin reorienta- tion temperatures. From the analysis of the obtained Mossbauer spectra it was deduced that in the region of transition each subspectrum was split into two Zeeman sextets, which were characterised by difierent hyperflne mag- netic flelds and quadrupole splittings. A consistent way of describing the Mossbauer spectra in the wide range of temperatures was proposed. The composition and temperature dependences of hyperflne interaction param- eters and subspectra contributions were derived from experimental spectra. The transition temperatures were determined for all the compounds studied and the spin phase diagram was constructed.

Spin glass-like state, charge ordering, phase diagram and positive entropy change in Nd 0.5−xPr xSr 0.5MnO 3 perovskites

The mixed rare earth manganites Nd 0.5− x Pr x Sr 0.5MnO 3 ( x=0.1–0.5) have been prepared using solid state reaction technique. All samples are of single phase with orthorhombic structure. The microstructure of the samples was determined by SEM. The field-cooled (FC) and zero-field-cooled (ZFC) curves showed that samples with x⩾0.25 exhibit the spin glass-like state at low field and low temperatures, whereas, in the samples with x<0.25, there is the charge ordering (coexisting with FM–AFM transition) established at low temperatures. The Curie temperature of the samples increases with increasing Pr content due to increase of < r A>. Interesting feature is that at the FM–AFM transition region, the magnetic entropy change has positive value, in contrary to that at FM–PM transition region. The electrical property of the samples from 10 K to room temperature is examined in detail.

Structure and magnetic properties of (Nd1－xGdx)3 Fe27.31Ti1.69 compounds

The structure and magnetic properties of (Nd1-xGdx)3Fe27.31Ti1.69 compounds have been investigated by means of X-ray diffraction and magnetic measurements. All compounds with x in the range of x≤0.6 crystallize in Nd3(Fe, Ti)29-type structure. Substitution of Gd for Nd leads to a contraction of unit-cell volume. The Curie temperature TC and anisotropy field Ba of the (Nd1-xGdx)3Fe27.31Ti1.69 compounds increases monotonically with increasing Gd content. Saturation magnetization Ms of the (Nd1-xGdx)3Fe27.31Ti1.69 compounds decreases with increasing x. As temperature lowers from room temperature to 5K, a spin reorientation from the easy plane to the easy cone occurs for (Nd1-xGdx)3Fe27.31Ti1.69 compounds. Spin phase diagrams have been constructed for (Nd1-xGdx)3Fe27.31Ti1.69 compounds.

Experimental studies of spin reorientations inEr2−xThxFe14B

Er2−xThxFe14B (x = 0.0, 0.5, 1.0, 1.5, 2.0) polycrystalline compounds have been studied with57Fe Mössbauer spectroscopy, differential scanning calorimetry (DSC), magnetic measurements andx-ray diffraction. Special emphasis was put on the spin reorientation phenomena (change ofspin orientation from planar to axial arrangement) occurring in this series when increasingtemperature. The spin reorientation in each compound has been investigated mainly bynarrow step temperature scanning in the vicinity of the spin reorientation temperature,TSR.Initial magnetization versus temperature measurements allowed us to establish thetemperature regions of reorientations and the Curie temperatures of the compounds. Thetwo-stage character of transitions was evidenced.Mössbauer temperature scanning was performed with a step of 2 K in the vicinity ofTSR. The obtained spectra were analysed by using a procedure of simultaneousfitting and the transmission integral approach. Consistent fits were obtained;TSR and the composition dependences of hyperfine interaction parameters were derived from fitsfor all studied compounds.DSC studies proved that the spin reorientations were accompanied by thermal effects for compositionx = 0.5. Transformationenthalpy and TSR were determined from these studies and the two-stage character of the transition wasconfirmed.The TSR obtained with different methods were compared and the spin phase diagram for the serieswas constructed.

Spin reorientation studies in Er 2− xGd xFe 14B

57Fe Mössbauer spectroscopy, differential scanning calorimetry (DSC), magnetic measurements and X-ray diffraction have been used to study the polycrystalline Er 2− x Gd x Fe 14B ( x = 0.0, 0.5, 1.0, 1.5) compounds. Special emphasis was put on the spin reorientation phenomena (change of spin orientation from planar to axial arrangement) occurring in this series. The spin reorientation in each compound has been investigated mainly by narrow step temperature scanning in the neighborhood of the spin reorientation temperature, T SR. Initial magnetization versus temperature measurements allowed to establish the temperature regions of reorientations and also the Curie temperatures of the compounds. Mössbauer temperature scanning was performed with a step of 1 K in the vicinity of T SR. The obtained spectra were analyzed by using a procedure of simultaneous fitting, and the transmission integral approach. Consistent fits were obtained, T SR and the composition dependencies of hyperfine interaction parameters were derived from fits for all studied compounds. DSC studies proved that the spin reorientations were accompanied by thermal effects. Transformation enthalpy and T SR were determined from these studies. The T SR obtained with different methods were compared and the spin phase diagram for the series was constructed.

Effective interactions, Fermi–Bose duality, and ground states of ultracold atomic vapors in tight de Broglie waveguides

Derivation of effective zero-range one-dimensional (1D) interactions between atoms in tight waveguides is reviewed, as is the Fermi–Bose mapping method for determination of exact and strongly-correlated many-body ground states of ultracold bosonic and fermionic atomic vapors in such waveguides, including spin degrees of freedom. Odd-wave 1D interactions derived from 3D p-wave scattering are included as well as the usual even-wave interactions derived from 3D s-wave scattering, with emphasis on the role of 3D Feshbach resonances for selectively enhancing s-wave or p-wave scattering so as to reach 1D confinement-induced resonances of the even and odd-wave interactions. A duality between 1D fermions and bosons with zero-range interactions suggested by Cheon and Shigehara is shown to hold for the effective 1D dynamics of a spinor Fermi gas with both even and odd-wave interactions and that of a spinor Bose gas with even and odd-wave interactions, with even(odd)-wave Bose coupling constants inversely related to odd(even)-wave Fermi coupling constants. Some recent applications of Fermi–Bose mapping to determination of many-body ground states of Bose gases and of both magnetically trapped, spin-aligned and optically trapped, spin-free Fermi gases are described, and a new generalized Fermi–Bose mapping is used to determine the phase diagram of ground-state total spin of the spinor Fermi gas as a function of its even and odd-wave coupling constants.

Spin patterns and phase diagrams of few (1 1 1)-monolayer EuTe including shape anisotropy

EuTe is a typical representative of the Heisenberg model, showing type-II antiferromagnetic ordering. In few monolayer samples grown by molecular-beam epitaxy, shape anisotropy plays a key role for magnetic ordering, especially in odd-layered systems which show drastically different phase diagrams for in-plane and perpendicular fields due to the remaining net magnetic moment in zero external field. Using a variational mean-field method based on the Bogoliubov-inequality, we show that the spin–flop like phases for either field directions are of completely different nature, treating a three-layer system as an example. The perpendicular spin–flop phase turns out to be a mixture between the conventional (isotropic) spin–flop and a novel tilted antiferromagnetic phase appearing only for low anisotropy.

Quantum spin- [formula omitted] two-dimensional XXZ model: an alternative quantum renormalization-group approach

We study the phase diagram of the two-dimensional quantum spin- 1 2 anisotropic Heisenberg model. We adapt a renormalization-group approach to treat this quantum model, and an analysis on low temperatures is presented and compared with the exact results in the isotropic limit, obtained from the Mermin–Wagner theorem. We comment on extensions of the procedure to treat antiferromagnetic models, for S= 1 2 and S> 1 2 .

Structural and Magnetic Properties of (Nd1‐xHox) 3Fe27.31Ti1.69 Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Crystal structure and spin-reorientation transition in TbFe 10− xNi xSi 2 compounds

The crystal structure and magnetic properties of TbFe 10− x Ni x Si 2 compounds have been investigated by means of X-ray diffraction and magnetic measurements. It is revealed that Ni substitution for Fe results in a slight variation of the Curie temperature, but a salient decrease of the spin-reorientation temperature of the compounds. A spin-phase diagram of TbFe 10− x Ni x Si 2 is constructed. At room temperature the compounds show planar magnetocrystalline anisotropy for x⩽1.5, but easy-axis anisotropy for x>1.5. Temperature dependent X-ray diffraction indicates a noticeable magnetostriction around the spin-reorientation temperature.

Structural and magnetic properties of (Nd1-xErx)3Fe273Ti17 compounds

Structural and magnetic properties of (Nd1-xErx)3Fe273Ti17 compounds have been investigated by means of x-ray diffraction and magnetic measurements. All the compounds with x in the range of 00—05 crystallize in a Nd3(Fe,Ti)29-type structure. Substitution of Er for Nd leads to a contraction of unit-cell volume. Curie temperature TC of the (Nd1-xErx)3Fe273Ti17 compounds decreases monotonically with increasing Er content. Saturation magnetization Ms of the (Nd1-xErx)3Fe273Ti17 compounds decreases with increasing x. As temperature decreases from room temperature to 5K, a spin reorientation from easy plane to easy cone occurs for (Nd1-xErx)3Fe273Ti17 compounds. The anisotropy field Ba for(Nd1-xErx)3Fe273Ti17 compounds decreases with increasing Er content. Spin-phase diagrams have been constructed for (Nd1-xErx)3Fe273Ti17 compounds.

Structure and anisotropy evolution in the (Nd 1− xEr x) 2Co 15.5V 1.5 system

The structure and magnetocrystalline anisotropy of (Nd 1− x Er x ) 2Co 15.5V 1.5 compounds have been investigated by means of X-ray diffraction and magnetic measurements. It is found that the (Nd 1− x Er x ) 2Co 15.5V 1.5 compounds crystallize in the Th 2Zn 17-type for x⩽0.3 and in the Th 2Ni 17-type structure for x⩾0.6. Both structures coexist for x=0.4 and 0.5. The Curie temperature shows a slightly decreasing tendency in both structures. The saturation magnetization M s at 5 K of the (Nd 1− x Er x ) 2Co 15.5V 1.5 compounds decreases monotonically with increasing Er content at a rate of 10.0 μ B / Er . A spin orientation was observed in the compounds with x=0–0.5 and the spin-reorientation temperature decreases with increasing Er content from 448 K for x=0 to 286 K for x=0.5. It is worth noting that the room-temperature magnetocrystalline anisotropy of the (Nd 1− x Er x ) 2Co 15.5V 1.5 compounds changes from easy-cone type for x<0.6 to the easy-axis type for x⩾0.6. A tentative spin phase diagram for the (Nd 1− x Er x ) 2Co 15.5V 1.5 compounds is presented.

Structural and magnetic properties of (Nd 1− xHo x) 3Fe 27.31Ti 1.69 compounds

Structural and magnetic properties of the (Nd 1− x Ho x ) 3Fe 27.31Ti 1.69 compounds have been investigated by means of X-ray diffraction and magnetic measurements. All the compounds with x≤0.6 crystallize in the Nd 3(Fe,Ti) 29-type structure. Substitution of Ho for Nd leads to a contraction of the unit-cell volume and a monotonic decrease of the saturation moments M s at 5 K. As the temperature decreases from room temperature to 5 K, a spin reorientation from easy plane to the easy cone occurs for all (Nd 1− x Ho x ) 3Fe 27.31Ti 1.69 compounds investigated. It has been found that the Curie temperature T C of the (Nd 1− x Ho x ) 3Fe 27.31Ti 1.69 compound almost has a constant value, whereas the spin reorientation temperature, T sr, decreases with increasing x. The anisotropy fields, B a, at room temperature for the (Nd 1− x Ho x ) 3Fe 27.31Ti 1.69 compounds have been determined by the singular point detection method and are found to be almost independent of the Ho content. A tentative spin phase diagram has been constructed for the (Nd 1− x Ho x ) 3Fe 27.31Ti 1.69 compounds.

Surface magnetism: phase transitions in quantum and classical models

We study the phase diagram and multicritical behavior of the semi-infinite quantum spin 1/2 anisotropic Heisenberg and classical O( n) models. We use correlated effective field theory. The multicritical point Δ c and the crossover exponent φ are obtained as a function of the value n and anisotropy parameter. We have compared the results of systems with ferromagnetic and antiferromagnetic interactions.

Phase Diagram of Spin-1/2 Ising Semi-Infinite and Film Ferromagnets with Spin-3/2 Overlayers

Within the framework of the effective field theory, we examine the phase diagrams of a spin-1/2 Ising film, with a spin-3/2 atoms on the top and bottom surfaces, and the corresponding semi-infinite system. In particular, the effects of surface single-ion anisotropy on the phase diagram and critical value for surface ordering are clarified. The system shows the existence of a critical value of the ratio of the surface interaction to the bulk one above which the surface magnetism appears. This critical value moves to lower values when D s increases. The critical surface temperature exhibits a characteristic behavior namely when large negative D s are selected.

Two-electron quantum dot molecule: composite particles and the spin phase diagram.

We study a two-electron quantum dot molecule in a magnetic field by the direct diagonalization of the Hamiltonian matrix. The ground states of the molecule with the total spin S = 0 and S = 1 provide a possible realization for a qubit of a quantum computer. Switching between the states is best achieved by changing the magnetic field. Based on an analysis of the wave function, we show that the system consists of composite particles formed by an electron and flux quanta attached to it. This picture can also be used to explain the spin phase diagram.

Spin Reorientation Studies in Nd2Fe14-xSixB (0&lt;x≤2)

Nd 2 Fe 1 4 - x Si x B (z = 0.25, 0.5, 0.75, 1.0, 1.5, 2.0) intermetallic compounds were investigated by magnetometry, 5 7 Fe Mossbauer effect, electric resistivity, and differential scanning calorimetry mainly in the vicinity of the spin reorientation temperature, T S R . The Curie temperature, T C , and T S R were determined for different compositions and the spin phase diagram was constructed. 5 7 Fe Mossbauer spectra showed noticeable changes in the reorientation region. For temperatures above the transition, the spectra were analysed using 6 Zeeman patterns associated with 6 inequivalent crystal sites in Nd 2 Fe 1 4 B according to site occupations (16k 1 :16k 2 :8j 1 :8j 2 :4c:4e)). In the transition region, 12 subspectra had to be incorporated in the analysis. Electric resistivity measurements showed a typical metallic behaviour with no anomalies in the magnetic transition region. Differential scanning calorimetry measurements revealed broad endothermic two stage peaks around T S R .

Structural and magnetic properties of (Nd1-xRx)3Fe27.31Ti1.69 compounds with R = Dy and Er

Structural and magnetic properties of (Nd1-xRx)3Fe27.31Ti1.69 compounds with R = Dy or Er have been investigated by means of x-ray diffraction andmagnetic measurements. All compounds with x⩽0.5 for R = Er or with x⩽0.6 for R = Dy crystallize in Nd3(Fe, Ti)29-type structure. Substitution of Er orDy for Nd leads to a contraction of unit-cell volume. The Curietemperature TC of (Nd1-xDyx)3Fe27.31Ti1.69 compounds increases almost linearly withincreasing Dy content, whereas TC of the (Nd1-xErx)3Fe27.31Ti1.69 compounds decreasesmonotonically with increasing Er content. Saturation moments Ms of the(Nd1-xRx)3Fe27.31Ti1.69compounds decrease with increasing x for both R = Er andDy. As temperature lowers from room temperature to 5 K, a spinreorientation from the easy plane to the easy cone occurs for (Nd1-xErx)3Fe27.31Ti1.69 and two spinreorientations from the easy plane to two different easy cones occur forthe (Nd1-xDyx)3Fe27.31Ti1.69compounds. The anisotropy field Ba at room temperature for(Nd1-xDyx)3Fe27.31Ti1.69compounds increases with increasing Dy content, whereas Ba for(Nd1-xErx)3Fe27.31Ti1.69compounds decreases with increasing Er content. Spin phase diagrams havebeen constructed for both (Nd1-xDyx)3Fe27.31Ti1.69 and (Nd1-xErx)3Fe27.31Ti1.69 compounds.

Study of the crossover from 2 to 3 dimensions in the quantum spin- [formula omitted] anisotropic Heisenberg model

The phase diagram of the quantum spin- 1 2 anisotropic Heisenberg antiferromagnet is studied, within a mean-field renormalization-group approach in larger clusters. The model consists of an anisotropic cubic lattice, with in-plane J and inter-plane J′= λJ interactions. The dependence of the Néel temperature T N on the interlayer coupling λ and on the anisotropy parameter Δ ( Δ=0 and 1 correspond to the isotropic Heisenberg and Ising models, respectively) is obtained explicitly. We have shown that T N ( Δ, λ) is different from the Curie temperature T c ( Δ, λ), such that, at Δ c ( λ) [or λ c ( Δ)], T c = T N . The set of points Δ c ( λ) determine a characteristic frontier in the ( λ, Δ) plane, which separate three regimes. These are defined as: Curie, when T c > T N , Néel, when T c < T N , and mixed, where the two previous regimes coexist.

Magnetic properties of the ErFe/sub 10-x/Ga/sub x/Si/sub 2/ compounds

The ErFe/sub 10-x/Ga/sub x/Si/sub 2/ compounds with the ThMn/sub 12/-type structure were synthesized for x=0.0, 0.5, 1.0, 1.5 and 2.0. With increasing Ga content, the lattice constant c and the unit-cell volume V increase monotonically. The lattice constant, a, and the Curie temperature increase first, go through a maximum and then decrease with increasing x. Spin re-orientation from the easy-cone to the uniaxial type is detected for all the compounds as the temperature increases from 5 to 300 K. A tentative spin phase diagram is constructed for ErFe/sub 10-x/Ga/sub x/Si/sub 2/. The saturation magnetization decreases monotonically which can be understood in terms of a simple dilution model.