A possible mechanism for large magnetostriction in manganite system

Autor: S.K. Ghatak, I. Chaudhuri
Rok vydání: 2003
Předmět:
Zdroj: Journal of Magnetism and Magnetic Materials. 261:442-448
ISSN: 0304-8853
DOI: 10.1016/s0304-8853(02)01495-6
Popis: Large magnetostriction has been observed in Ca-doped manganites within a range of doping. A large strain that appears at higher temperature markedly decreases as ferromagnetic phase sets in at low temperature. The strain vanishes below Tc at a critical magnetic field which is a decreasing function of temperature. For T>Tc the strain is slowly released in presence of magnetic field. A model is considered where the eg electron is coupled to lattice through Jahn–Teller mechanism and its itinerancy is governed by double exchange. A possible mechanism for the magnetostriction is proposed considering two competing aspects such as the Jahn–Teller coupling and enhanced itinerancy governed by double exchange of eg electron of Mn-ion. The Hamiltonian for eg electron consists of the Jahn–Teller interaction, intra-atomic coulomb and exchange interactions and hopping term. Assuming the hopping integral tij ∝ 〈Si·Sj〉1/2, nearest-neighbour spin–spin correlation which is calculated in pair approximation and using mean field approximation for Coulomb and exchange interaction, the thermal and field dependence of the strain is calculated. The strain appears spontaneously when gain in electronic energy due to the removal of degeneracy outweighs the cost of elastic energy. However, increase in kinetic energy resulting from correlated hopping in ferromagnetic state or in presence of magnetic field tends to suppress the strain. The abrupt decrease of magnetostriction induced by an external magnetic field below Tc is revealed from this model. Above Tc'slower decrease with quadratic field dependence is found. These results are qualitatively in tune with the experimental observation of (Nd1−y Smy)1/2Sr1/2MnO3 (y=0.938).
Databáze: OpenAIRE
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