- Mona Jani: “Superdiamagnetism” in materials with coexisting ferromagnetic and antiferromagnetic interactions
- 15. 11. 2017, 14:30
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
Apparent diamagnetic response has been reported for various materials that possess both antiferromagnetic (AFM) and ferromagnetic (FM) components of spin ordering e.g. [1, 2]. However, the origin of anomalously large diamagnetic moment is not yet clarified. In the presentation, I will report on the "super-diamagnetic" response measured for single- and poly- crystals of FeS2 and NiS2 below the transition temperatures Tc ~ TN ~ 60 K and 30 K, where AFM and FM orders coexist. The field-cooled (fc) magnetization Mfc(T) revealed a characteristic for FM materials behavior for T < Tc. The FM ordering has been confirmed by means of M(H) hysteresis loop measurements. Samples do not exhibit superconductivity as resistivity measurement revealed semiconducting behavior in the entire temperature range investigated. For FeS2 and NiS2 we observe irreversible magnetoresistance behavior. The resistance R(T) of compressed FeS2 powders follows R ~ exp(const/T1/2), up to the room temperature, expected for the Efros-Shklovskii variable range hopping regime in the presence of a Coulomb gap. NiS2 is one of the best examples of a Mott insulator where spontaneous circular electric currents are expected [3], and our electric transport measurements strongly suggest the importance of Coulomb interactions in the anomalous diamagnetic state. We provide an experimental evidence for competing diamagnetic and ferromagnetic responses and discuss the results within available theoretical models [3, 4].
References:
[1] A. V. Mahajan et al., Phys. Rev. B 46, 10966 (1992).
[2] Y. Ren et al., Nature 396, 441 (1998).
[3] L. N. Bulaevskii et al., Phys. Rev. B 78, 024402 (2008).
[4] H. Koizumi, Physica C 470, S118 (2010).
R. R. da Silva and Y. Kopelevich
Work done at: Instituto de Física "Gleb Wataghin", Universidade Estadual de Campinas (UNICAMP), Campinas- 13083859, S?o Paulo, Brasil - advisor (Prof. Y. Kopelevich), collaborator Dr. R. R. da Silva