| Popis: |
Spin-glass is a disordered magnetic state, where the spins of the component atoms are not aligned in a regular pattern. Their randomness basically comes from the competition between different magnetic interactions. Mathematical complexity of spin-glass structures is the main reason why complete microscopic theory of such systems still doesn't exist, while there are many phenomena related to it, observable if proper material system is found. [1] Chromium niobate (CrNbO 4 ) of the rutile-type structure was synthesized by pyrolysis of the oxalate-based heterobimetallic complex molecular precursor [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H2O (bpy = 2, 2'-bipyridine). [2] Compared to the conventional solid state reactions, this represents a simple one-step route to synthesize pure material and at lower temperatures. Magnetic behaviour of this oxide was investigated by SQUID magnetometer. Magnetization indicates occurrence of the spin-glass state at 9.3 K. Spins of Cr 3+ ions dominantly interact antiferromagnetically, while hysteresis curves suggest some additional interactions consistent with spin-glass structure, which is confirmed with other magnetic parameters, too. The most interesting is the non-ergodic behaviour observed through the specific relaxation of magnetization and peculiar memory effect. Ability to see all these phenomena might be found in the way of synthesis on the molecular level. Similar behaviour was observed in CrTaO 4 , but below 3.5 K, and even more interesting in some multiferroic material [3]. As CrNbO 4 and CrTaO 4 have specific electric and catalytic properties, new opportunities arise if spin-glass phase is combined with other spin-dependent processes in such multi-functional materials. [1] J. A. Mydosh, Spin glasses: an experimental introduction, Taylor-Francis, London, 1993. [2] L. Androš Dubraja et. al., Single-step preparation of rutile-type CrNbO 4 and CrTaO 4 oxides from oxalate precursors–characterization and properties, Accepted in J. Am. Ceram Soc. 2019. [3] Z. Jagličić et. al., Appl. Phys. Lett. 102 (2013) 242410. |
