Magnetic properties of the ferrimagnetic spinels systems CoFe2–2xCr2xO4

The magnetic properties of a diluted ferrimagnetic spinels system CoFe2–2xCr2xO4 are studied using the high-temperature series expansions method in the range 0 ≤ x ≤ 1. The inter-sublattice exchange interactions (JCo Cr or JCo–Fe) are calculated using the probability law. The high-temperature series expansions, together with the Padé-approximants method, are applied to the spinels systems CoFe2–2xCr2xO4 to determine the magnetic phase diagram, i.e., TC versus dilution x. The critical exponent associated with the magnetic susceptibility (γ) is deduced. PACS Nos.: 75.30.Et; 75.40.Cx; 74.25.Ha, 75.30.Cr

Topological phase transitions in frustrated magnets

The role of topological excitations in frustrated Heisenberg antiferromagnets between two and three spatial dimensions is considered. In particular, the antiferromagnetic Heisenberg model on a stacked triangular geometry with a finite number of layers is studied using Monte Carlo methods. A phase transition that is purely topological in nature occurs at a finite temperature for all film thicknesses. The results indicate that topological excitations are important for a complete understanding of the critical properties of the model between two and three dimensions. PACS Nos.: 75.10.Hk, 75.40.Cx, 75.40.Mg

Investigation of the elastic properties of UNI2Si2 as a function of temperature, magnetic field, and pressure

It is now well-established that the strong anisotropy in the magnetic properties of the intermetallic compounds UT2Si2, where T stands for a transition metal, is responsible for their rich magnetic phase diagram. However, within that series of compounds, UNi2Si2 is one that shows an unusual sequence of magnetically ordered states. Thus, to better understand its unusual properties, we have investigated the elastic properties of UNi2Si2 as a function of temperature, magnetic field, and pressure. In all three magnetic phases, our measurements indicate that the sound-velocity temperature dependence is dominated by the magnetoelastic coupling. Moreover, the analysis of the temperature dependence for the incommensurate longitudinal spin-density wave phase is consistent with a critical exponent β = 0.38 ± 0.01. We also present the magnetic phase diagram for UNi2Si2 obtained at 0 and 8 kbar. Our investigation reveals that the triple-point coordinates (Tp, Hp) decrease with pressure at a rate of dTp/dP = –0.1 K/kbar and dHp/dP = –0.1 T/kbar, respectively. PACS Nos.: 75.30.kz, 62.20.Dc, 62.50.+p, 75.40.Cx