Three-dimensional Heisenberg Antiferromagnet Research Articles

Nonmagnetic impurities in two- and three-dimensional Heisenberg antiferromagnets.

In this paper we study in a large-S expansion effects of substituting spins by non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets in a weak magnetic field. In particular, we demonstrate a novel mechanism where magnetic moments are induced around non-magnetic impurities when magnetic field is present. As a result, Curie-type behaviour in magnetic susceptibility can be observed well below the Neel temperature, in agreement with what is being observed in $La_2Cu_{1-x}Zn_{x}O_4$ and $Sr(Cu_{1-x}Zn_x)_2O_3$ compounds.

Spin correlations in percolating networks with fractal geometry

Using neutron-scattering techniques, we have investigated the magnetic correlations in dilute antiferromagnets close to the percolation threshold, in which the magnetic connectivity takes a fractal form. Recent experimental results concerning the self-similarity of the magnetic order, and magnetic excitations in two-dimensional Ising and threedimensional Heisenberg antiferromagnets are presented.

Magnetic structures of the three-dimensional Heisenberg antiferromagnets K2FeCl5.D2O and Rb2FeCl5.D2O

The crystal and magnetic structures of K2FeCl5.D2O and Rb2FeCl5/D2O have been determined by neutron powder diffraction. The crystal structure of K2FeCl5.D2O has been redetermined using single-crystal diffraction. All compounds crystallize with the orthorhombic space group Pnma. The magnetic structure of both deuterated compounds can be described by ferromagnetic planes perpendicular to the b axis coupled antiferromagnetically to each other. The critical behaviour of the staggered magnetization below TN=14.2 K and 10.0 K for K2FeCl5.D2O and Rb2FeCl5.D2O, respectively, can be described by a power law for reduced temperature 0.03<t<0.2 by a critical exponent beta =0.35+or-0.02.

Magnetochemistry of the tetrahaloferrate(III) ions. 6. Crystal structure and magnetic ordering in [(pyH) 3Cl][FeCl 4] 2

The crystal structure, magnetic susceptibilities and specific heat of the title compound were determined by X-ray diffraction, susceptometry between 1.2 and 20 K, and adiabatic calorimetry between 1.5 and 39 K, respectively. The material is found to be a canted antiferromagnet with a critical temperature of 2.212 K. A λ-feature in the heat capacity at that temperature and an apparent break in the susceptibility curves are indicative of the manifestation of long-range order. A large degree of short-range order is observed to persist above the critical temperature, however. The compound crystallizes in the orthorhombic space group Pbca ( Z=8, a=13.040(2), b=15.929(2), c=27.014(5) Å and V=5611.2 Å 3). Bond lengths average 2.184(5) and 2.185(2) Å for Fe(1)Cl and Fe(2)Cl, respectively, within the slightly distorted tetrahedra. Single crystal magnetic susceptibility measurements of the sample show behavior consistent with that of a three-dimensional Heisenberg antiferromagnet with a small ferromagnetic peak whose maximum is identified at 2.00(1) K. This behavior is indicative of sublattice canting. A fit of the data from high temperature series expansions for a Heisenberg S=5/2 simple cubic lattice gives | J|/ k B=0.084(1) K with g=2.00.

Magnetochemistry of the tetrahaloferrate (III) ions: Crystal structure and magnetic ordering in [(4-chloropyridinium)FeCl4]2⋅4-chloropyridinium chloride and related salts (abstract)

The yellow compound of stoichiometry (4-chloropyridinium)3Fe2Cl9 belongs to the space group P21/n with four formula units in the unit cell. Structural analysis shows that the iron is present as the FeX4− ion. Magnetic measurements on single crystals show that the material orders as a canted antiferromagnet at 2.725 K. Replacement of the 4-chloro cation by the 4-bromo analog yields an isomorphous material and shifts the transition temperature to 2.34 K. The phase diagrams of both salts have also been determined. For [(4-chloropyridinium)FeCl4]2⋅4-chloropyridinium chloride, the bicritical point is at 2.40 K and 7 kOe, and HSF(0)=5.5 kOe. With Hc(0)=56 kOe, α=HA/HE=1.9×10−2. In the case of [(4-bromopyridinium)FeCl4]2⋅4-bromopyridinium chloride, HSF(0)=3 kOe, Hc(0)=42 kOe, α=1.0×10−2, and the bicritical point is at 2.24 K and 4.2 kOe. Crystallographic investigations at 25 K are reported on the isomorphous (4-chloropyridinium)3Fe2Br9 and on (4-bromopyridinium)3Fe2Cl1.3Br7.7. Magnetic measurements on single crystals show that (4-bromopyridinium)3Fe2Cl1.3Br7.7 orders as a canted antiferromagnet at 5.67 K, while (4-chloropyridinium)3Fe2Br9 orders similarly at 7.96 K. These compounds behave approximately as S=5/2, three-dimensional Heisenberg antiferromagnets.

Renormalization-Group Approach to the Frustrated Heisenberg Antiferromagnet on the Layered-Triangular Lattice

Renormalization-group e expansion is carried out for the n -component classical Heisenberg antiferromagnet on the d -dimensional layered-triangular lattice where the frustrated triangular nets are stacked along the remaining d -2 directions making a cubic structure. The associated Landau-Ginzburg-Wilson Hamiltonian is derived, which has essentially the same form as the one derived by Jones et al. for the superfluidity phase transition of helium 3. To O(e), four fixed points are found. Frustration is relevant only in one of these fixed points which is stable for larger values of n , i.e., n >21.8. In the Heisenberg case n =3, no stable fixed point is found. To O(e 2 ), however, the stability region of the fixed point where the frustration is relevant is considerably widend at finite e. Some discussions are given on the nature of phase transition of the three-dimensional triangular-lattice Heisenberg antiferromagnet.

Phase Transition of the Three-Dimensional Heisenberg Antiferromagnet on the Layered-Triangular Lattice

Phase transition of the frustrated X Y (plane rotator) antiferromagnet on the three-dimensional layered-triangular lattice is studied with use of a symmetry argument and a Monte Carlo simulation. A second-order transition of a new universality class is found with the exponents α≃0.44, β≃0.22, γ≃1.1 and ν≃0.52. Certain types of canted or helical magnets are predicted to belong to the same universality class.

Magnetic susceptibilities below 1 K: antiferromagnetic ordering in [Cu en 3]SO 4

The susceptibilities parallel and perpendicular to the room-temperature c axis of [Cu en 3]SO 4 have been measured over the temperature interval 40 mK − 4.2 K. Antiferromagnetic ordering is found to occur at 109 mK, with the easy axis essentially parallel to the c axis. The compound orders as a three-dimensional Heisenberg antiferromagnet, with J/k B ≈ −0.03 K.

Crossover behavior of the magnetic phase boundary of the low-anisotropy antiferromagnet KNiF3

The ordering temperature ${T}_{c}$ of the low-anisotropy cubic antiferromagnet KNi${\mathrm{F}}_{3}$ was measured as a function of magnetic field $H$, up to 180 kOe. At any fixed $H$, ${T}_{c}$ was determined from the $\ensuremath{\lambda}$ anomaly in the thermal-expansion coefficient. The transition temperature ${T}_{c}$ increased monotonically with increasing $H$. At the maximum field of 180 kOe, ${T}_{c}$ was 0.18 K higher than the N\'eel temperature ${T}_{N}=246.4$ K. The observed phase boundary ${T}_{c}(H)$ is in qualitative agreement with that predicted by Fisher, Nelson, and Kosterlitz for the fully isotropic three-dimensional Heisenberg antiferromagnet. The increase of ${T}_{c}$ with increasing $H$ is attributed to a crossover from a Heisenberg-like transition at $H=0$ to an $\mathrm{XY}$-like transition at finite $H$. Magnetostriction data, taken below ${T}_{N}$, suggest a tetragonal lattice distortion of order ${10}^{\ensuremath{-}4}$ at $T\ensuremath{\ll}{T}_{N}$.

Magnetic linear birefringence of one- and three-dimensional Heisenberg antiferromagnets: CsMnCl 3·2H 2O and Mn 1− cZn cF 2

The linear magnetic birefringence (LMB) has been studied on quasi-Heisenberg systems of different lattice dimensionality. In the linear-chain antiferromagnet CsMnCl 3·2H 2O ( T N = 4.9 K), the short-range order is still demonstrable at 130 K. The temperature derivative of the LMB has been compared with the theoretical magnetic specific heat and the intrachain exchange has been determined to have the value | J|/ k = 3.13 ± 0.15 K. In the mixed system Mn 1- c Zn c F 2 the proportionality between LMB and magnetic energy is given for all c. In crystals with a high Zn concentration only short-range order effects are present.