The impact of magnetoelasticity on structural phase transitions in cubic ferromagnets
Influence of the magnetoelastic interaction on the structural phase transitions in cubic ferromagnets is investigated on the basis of a Ginzburg-Landau theory. It is shown that for the case of a positive magnetic anisotropy constant the structural phase transitions are not accompanied by a spin-reorientation. In the magnetic state the high-temperature phase has small deformations caused by the magnetostriction. For the case of a strong magnetoelastic coupling these deformations lead to vanishing of the first order structural transitions. Corresponding critical points are determined. Due to the magnetoelastic interaction a first order magnetic phase transition can occur simultaneously with a structural first order transformation. The constrained theory allows to calculate a realistic (T,x)-phase diagram for Ni2+xMn1−xGa alloys. 64.10.+h, 64.70.Kb, 75.30.Gw, 75.80.+q Typeset using REVTEX 1
The Landau theory of phase transitions: A mechanical analog
The Landau theory of phase transitions occupies a centerpiece position in physics. We illustrate the theory by a pedagogical example at the pre-university level. In the example a bead of mass is threaded on a ring which is set rotating about a vertical diameter. The dynamics of the bead mimics key features of the Landau theory.
Thermally Induced Dynamics of Satellite Solar Panels
Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.