Anomalous temperature and field behaviors of magnetization in cubic lattice frustrated ferromagnets

摘要

Thermodynamic properties of cubic Heisenberg ferromagnets with competingexchange interactions are considered near the frustration point where thecoefficient $D$ in the spin-wave spectrum $E_{\mathbf{k}}\sim D k^{2}$vanishes. Within the Dyson-Maleev formalism it is found that at lowtemperatures thermal fluctuations stabilize ferromagnetism by increasing thevalue of $D$. For not too strong frustration this leads to an unusual "concave"shape of the temperature dependence of magnetization, which is in agreementwith experimental data on the europium chalcogenides. Anomalous temperaturebehavior of magnetization is confirmed by Monte Carlo simulation. Strong fielddependence of magnetization (paraprocess) at finite temperature is found nearthe frustration point.