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Register a new userTemperature dependence of uniform static magnetic susceptibility in a two-dimensional quantum Heisenberg antiferromagnetic model
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A perturbation spin-wave theory for the quantum Heisenberg antiferromagnets on a square lattice is proposed to calculate the uniform static magnetic susceptibility at finite temperatures, where a divergence in the previous theories due to an artificial phase transition has been removed. To the zeroth order, the main features of the uniform static susceptibility are produced: a linear temperature dependence at low temperatures and a smooth crossover in the intermediate range and the Curie law at high temperatures. When the leading corrections from the spin-wave interactions are included, the resulting spin susceptibility in the full temperature range is in agreement with the numerical quantum Monte Carlo simulations and high-temperature series expansions.
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A universal linear-temperature dependence of the uniform magnetic susceptibility has been observed in the nonmagnetic normal state of iron-pnictides. This non-Pauli and non-Curie-Weiss-like paramagnetic behavior cannot be understood within a pure itinerant picture. We argue that it results from the existence of a wide antiferromagnetic fluctuation window in which the local spin-density-wave correlations exist but the global directional order has not been established yet.
We show that antiferromagnetic susceptibility in ferritin increases with temperature between 4.2 K and 180 K (i. e. below the N{e}el temperature) when taken as the derivative of the magnetization at high fields ($30times10^4$ Oe). This behavior contrasts with the decrease in temperature previously found, where the susceptibility was determined at lower fields ($5times10^4$ Oe). At high fields (up to $50 times10^4$ Oe) the temperature dependence of the antiferromagnetic susceptibility in ferritin nanoparticles approaches the normal behavior of bulk antiferromagnets and nanoparticles considering superantiferromagnetism, this latter leading to a better agreement at high field and low temperature. The contrast with the previous results is due to the insufficient field range used ($< 5 times10^4$ Oe), not enough to saturate the ferritin uncompensated moment.
The correlated spin dynamics and the temperature dependence of the correlation length $xi(T)$ in two-dimensional quantum ($S=1/2$) Heisenberg antiferromagnets (2DQHAF) on square lattice are discussed in the light of experimental results of proton spin lattice relaxation in copper formiate tetradeuterate (CFTD). In this compound the exchange constant is much smaller than the one in recently studied 2DQHAF, such as La$_2$CuO$_4$ and Sr$_2$CuO$_2$Cl$_2$. Thus the spin dynamics can be probed in detail over a wider temperature range. The NMR relaxation rates turn out in excellent agreement with a theoretical mode-coupling calculation. The deduced temperature behavior of $xi(T)$ is in agreement with high-temperature expansions, quantum Monte Carlo simulations and the pure quantum self-consistent harmonic approximation. Contrary to the predictions of the theories based on the Non-Linear $sigma$ Model, no evidence of crossover between different quantum regimes is observed.
We consider the non-analytic terms in the spin susceptibility arising as a result of rescaterring of pairs of quasiparticles. We emphasize the importance of rescattering in the Cooper channel for the analysis of the temperature dependences in the two-dimensional electron systems in the ballistic regime. In the calculation of the linear in $T$ term we use angular harmonics in the Cooper channel, because for each harmonic the interaction amplitude is renormalized independently. We observe, that as a consequence of strong renormalizations in the Cooper ladder, the temperature derivative of the spin susceptibility may change its sign at low temperatures.
We investigated effects of magnetic field H on antiferromagnetic (AF) structures in CeRh_{1-x}Co_xIn_5 by performing the elastic neutron scattering measurements. By applying H along the [1,-1,0] direction, the incommensurate AF state with the propagation vector of q_{h1}=(1/2,1/2,0.297) observed at H=0 is replaced by the commensurate AF state with the q_{c2} = (1/2, 1/2, 1/4) modulation above 2 T for x=0.23, while the AF states with the q_{c1}=(1/2,1/2,1/2) and q_{h2}=(1/2,1/2,0.42) modulations seen at H=0 change into a single q_{c1}-AF state above ~1.6 T for x=0.7. These results suggest the different types of AF correlation for Co concentrations of 0.23 and 0.7 in an applied magnetic field H.
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