Phase Diagram Of Spin-1 Research Articles

Theoretical study of the random mixed bond spin [formula omitted] Ising model

The phase diagrams of a random mixed bond spin 3 2 Ising model is studied using a new technique in effective field theory that employs a probability distribution within the framework of single-site cluster theory based on the use of ecaxt Ising spin identities. A model is adopted in which the nearest neighbour exchange coupling are independent random variables distributed according to the law P( J ij ) = pδ( J ij − J) + (1 − p) δ( J ij − αJ). General formulate applicabe to structures with arbitrary coordination number N are given. In a certain range of negative values of α, we found re-entrant phase diagrams and the threshold p ∗ at which the critical temperature goes to zero depends on α.

Spin excitations, phonons and phase diagram in high-T c cuprates

The implications of the slave-boson mean-field theory for the extended t-J model are summarised and compared with various experiments on spin fluctuations and certain phonon modes in high-Tc cuprates, placing special emphasis on the spin-gap phenomenon.

High-field magnetization process of Sm2(Fe1−xGax)17 compounds

The high-field magnetization process of Sm2(Fe1−xGax)17 compounds (x = 0 – 0.5) has been investigated. Substitution of Ga for Fe leads to an increase of the spin reorientation temperature. A tentative spin phase diagram is proposed. The magnetization of magnetically aligned samples was measured at 4.2 K in quasi-static fields up to 21 T.

Magnetic and electrical properties of(Er/sub 1-x/Pr/sub x/)/sub 2/Fe/sub 17/N/sub y/

A nitrogenation facility working in the pressure range 0-100 bar and temperature range 30-600/spl deg/C was fabricated and the nitrides were prepared. There is an increase in the unit cell volume by about 8% for a nitrogen concentration of 2.7. Similarly there is an increase in the magnetization as well as the Curie temperature after nitrogenation for all the compounds. The increase in the magnetization is due to the increase in the average Fe moment as a result of lattice expansion following nitrogenation. The increase in the Curie temperature is explained on the basis of spin fluctuation theory. A tentative spin phase diagram is proposed based on the magnetization and AC magnetic susceptibility measurements. Upon nitrogenation, the resistivity of the samples increases by one order of magnitude still retaining the metallic behaviour.

Spin excitations and phase diagram of the extended t-J model

The results of theoretical studies of spin excitations in the extended t-J model treated by the slave-boson mean-field theory are briefly summarized and compared with experimental results of neutron scattering and nuclear magnetic resonance, for both LSCO and YBCO.

Magnetic properties of Er2Fe17−xAlxNy compounds

Structural and magnetic properties of the Er2Fe17−xAlxNy compounds (0≤x≤3) have been investigated. All nitrides and parent compounds crystallize in the Th2Ni17 structure. Al substituted for Fe leads to an increase in lattice constants a and c. Introduction of nitrogen results in a further increase of lattice constants, but the magnitude of this increase is smaller for increasing x. As Al content increases, the Curie temperature of the parent compound increases, whereas the Curie temperature of the nitride decreases. The substitution of Al for Fe results in a decrease of Fe moment in both nitrides and parent compounds. Introduction of nitrogen leads to an increase in the uniaxial anisotropy of the Er sublattice and a spin reorientation. A tentative spin phase diagram has been constructed.

Magnetic properties of (Er,R)2Fe17Ny compounds (R=Y,Gd)

Structural and magnetic properties of the interstitial (Er1−xRx)2Fe17Ny compounds with R=Y and Gd, x=0, 0.1, 0.25, 0.4, 0.5, 0.6, 0.75, and 1.0, 2<y<3, have been investigated. All the parent compounds crystallize in the Th2Ni17-type structure, except for Gd2Fe17 which crystallizes in the Th2Zn17-structure. All nitrides preserve the same structure as the parents. Introduction of nitrogen results in an increase in lattice constants a and c, and the expansion of unit-cell volume is about 6%. The Curie temperature was found to increase distinctly after nitrogenation. Nitrogen absorption leads to an increase in saturation magnetization, the values of the saturation magnetization increase monotonically with increasing Y or Gd concentration. Nitrogenation increases the uniaxial anisotropy of the Er sublattice, and causes a spin reorientation. The Y and Gd concentration dependencies of the spin reorientation temperature Tsr exhibit maxima. The tentative spin phase diagrams are presented.

The random mixed bond spin 1 Ising model

The ferromagnetic phase diagram of a random mixed bond spin 1 Ising model is investigated within the framework of an effective field theory that correctly amounts for the single site spin kinematic relations. A model is adopted in which the nearest neighbour exchange coupling are described by the probability distribution P( J ij ) = pδ( J ij − J) + (1 − p) δ( J ij − αJ). General formulae applicable to structures with arbitrary coordination number are given. The case when α is negative is examined in detail, particular attention being paid to the critical ferromagnetic bond concentration at which the ferromagnetic phase breaks down. Results for the ferromagnetic critical frontier are presented for the honeycomb, square and cubic lattices.

Tricritical behavior of a mixed spin- and spin-2 Ising system

Abstract The phase diagram of a mixed spin- 1 2 and spin-2 Ising system is investigated by the use of the effective-field theory. The general expression for evaluating the transition temperature and the tricritical point is obtained. We find that the tricritical point exists in the system when the coordination number z is larger than z = 3.

Structure and magnetic properties of Er/sub 2/Fe/sub 17/C/sub x/ compounds

The interstitial carbides of Er/sub 2/Fe/sub 17/C/sub x/ with x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 have been synthesized by arc melting and by the Gas-Phase Interaction (GPI) method. The unit-cell volume of the compounds is found to increase with increasing carbon concentration. The dependence of Curie temperatures, spin-reorientation temperatures and the magnetic coupling on the carbon content has been investigated. The spin phase diagram of the series is given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

FUSED POTTS MODELS

Generalizing the mapping between the Potts model with nearest neighbor interaction and the six-vertex model, we build a family of “fused Potts models” related to the spin k/2 U q su (2) invariant vertex model and quantum spin chain. These Potts models still have variables taking values 1, …,Q[Formula: see text] but they have a set of complicated multispin interactions. The general technique to compute these interactions, the resulting lattice geometry, symmetries, and the detailed examples of k=2, 3 are given. For Q&gt;4, spontaneous magnetizations are computed on the integrable first order phase transition line, generalizing Baxter’s results for k=1. For Q≤4, we discuss the full phase diagram of the spin 1 (k=2) anisotropic and U q su (2) invariant quantum spin chain [it reduces in the limit Q=4 (q=1) to the much studied phase diagram of the isotropic spin 1 quantum spin chain], Several critical lines and massless phases are exhibited. The appropriate generalization of the valence bond state method of Affleck et al. is worked out.

Analysis of spin-phase diagrams for RxY1-xCo5 (R identical to Pr, Tb, Dy and Ho) and RxPr1-xCo5 (R identical to Sm, Gd, Tb, Dy, Ho and Er)

The spin-phase diagrams for the pseudo-binary compounds of RxY1-xCo5 (R identical to Pr, Tb, Dy and Ho) and RxPr1-xCo5 (R identical to Sm, Gd, Tb, Dy, Ho and Er) are reproduced well by the calculations which use the fitted R-Co exchange field and CEF parameters evaluated previously by some of the authors of this paper and co-workers by comparing the calculations with other experimental data.

Magnetic properties of RFe 12- xV x (R = Y, Nd) compounds

The magnetic properties of RFe 12- x V x (R = Y, Nd; x = 1.5, 1.75, 2.0, 2.25, 2.5) compounds have been studied. All compounds crystallize in the ThMn 12 structure with α-Fe as impurity phase. In both Y(Fe, V) 12 and Nd(Fe, V) 12, the Curie temperatures and magnetic moments decrease monotonically with increasing V content. The spin reorientation temperatures in the Nd(Fe, V) 12 compounds also decrease with increasing V content. A tentative spin phase diagram for the NdFe 12- x V x series is presented.

Phase diagram and paramagnetic susceptibility of spin [formula omitted] Blume-Capel model in the correlated effective-field treatment

The phase diagram and paramagnetic susceptibility of the spin 3 2 Blume-Capel model are investigated within the statistical accuracy of the Bethe-Peierls approximation (or the correlated effective field treatment). In particular, the inverse paramagnetic susceptibility may show an outstanding feature in the special region of a negative crystal-field constant.

Surface phase diagrams of the semi-infinite Ising model with a surface amorphization

Surface phase diagrams of the semi-infinite spin- 1 2 Ising ferromagnet with a surface amorphization are investigated by the use of the finite-cluster renormalization method. In this method we take into account a relation like 〈σ 2 i 〉 = 1 into the exact correlati on function identity for finite clusters of spins and results are combined with renormalization-group ideas. We find a number of characteristic behaviours for the surface magnetic proporties such as the possibility of the surface re-entrant phenomenon.

Nuclear magnetic resonance study of (Y 1− xR x) 2Co 14B compounds (R  Gd, Tb)

Influence of the Gd spin on the Co hyperfine field has been studied by 59Co nuclear magnetic resonance (NMR) in (Y 1− x Gd x ) 2Co 14B compounds. It is shown that the hyperfine coupling constants from the Gd spin for 8j 1 and 8j 2 sites are negative while those for 16k 1 and 16k 2 sites are positive. The dependence of the spin orientation temperature on the non-magnetic Y concentration in (Y 1− x Tb x ) 2Co 14B is also investigated by magnetization and 59Co NMR measurements. A spin phase diagram for this compound is proposed.

Magnetic properties of (Sm/sub 1-x/R/sub x/)/sub 2/ Fe/sub 17/N/sub y/ (R=Dy, Er) compounds

The effects of the substitutions of Dy and Er for Sm on the crystal structure and magnetic properties of Sm/sub 2/Fe/sub 17/ and Sm/sub 2/Fe/sub 17/N/sub y/ compounds have been investigated. The structures of (Sm/sub 1-x/R/sub x/)/sub 2/ Fe/sub 17/N/sub y/ compounds with R=Dy and Er and the hosts change from Th/sub 2/Zn/sub 17/-type to Th/sub 2/Ni/sub 17/-type with increasing Dy and Er contents. The replacement of Sm by Dy or Er results in a decrease in Curie temperature, saturation magnetization, and magnetic anisotropy field in the (Sm/sub 1-x/R/sub x/)/sub 2/Fe/sub 17/N/sub y/ compounds. A tentative spin phase diagram of the (Sm/sub 1-x/Dy/sub x/)/sub 2/Fe/sub 17/N/sub y/ compounds is suggested.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High field magnetization process of (Sm, Nd) 2Fe 17N y compounds

The crystal structure and high-field magnetization process of (Sm 1− x Nd x ) 2Fe 17N y compounds ( x=0.0, 0.1,…, 1.0, 2< y<3) have been investigated. X-ray diffraction patterns of random and magnetically aligned powder samples were obtained. The magnetizations were measured in steady fields up to 7 T at temperatures ranging from 1.5 K to room temperature and in quasi-static fields up to 35 T at 4.2 K and 77 K. All (Sm 1− x Nd x ) 2Fe 17N y compounds were found to crystallize in the rhombohedral Th 2Zn 17 structure. As x increases, the Curie temperature decreases. The anisotropy fields and easy magnetization direction were investigated from 1.5 K to room temperature by means of high-field magnetization measurements and AC-susceptibility measurements, combined with X-ray diffraction on random and magnetically aligned powder samples. The anisotropy field decreases with increasing x and approaches a minimum value at about x=0.6, then increases again. A tentative spin phase diagram for the (Sm 1− x Nd x ) 2Fe 17N y series is presented. At room temperature, the easy magnetization direction remains along the c-axis up to x=0.6.

Magnetic anisotropy of (Sm, Y) 2Fe 17N y compounds

A study of the crystal structure and the magnetic properties, especially the magnetocrystalline anisotropy of (Sm 1− x Y x ) 2Fe 17N y compounds ( x=0, 0.2, 0.4, 0.6, 0.8, and 1.0, 2< y<3) has been performed. All the interstitially nitrided compounds preserve the same Th 2Zn 17- or Th 2Ni 17-type structure as the original compounds. The Curie temperatures decrease from 750 to 700 K as x increases from 0 to 1. The anisotropy field decreases linearly with increasing yttrium content. The spin reorientation has been investigated by means of high field magnetization measurements, AC-susceptibility measurements and thermomagnetic analysis, combined with X-ray diffraction. The anisotropy constants K 1, K 2 and K 3 were derived by a phenomenological analysis, using magnetization curves measured in high fields, applied perpendicular to the alignment direction of the powder samples. A tentative spin phase diagram of the series is presented.

Spin reorientations in (Nd 1− xR x) 2Co 14B compounds

Magnetization measurements and 59Co NMR have been performed for (Nd 1− x R x ) 2Co 14B(R=Y, Pr, Sm, Gd and Tb) compounds. Three types of the spin phase diagrams, depending on the sign of the Stevens factor of the R ion, have been established based on these measurements. The results are discussed with the crystalline electric field (CEF) approximation.