Size mismatch: A crucial factor for generating a spin-glass insulator in manganites

Abstract

The structural, electronic, and magnetic properties of the highly mismatched perovskite oxides, Th 0.35 A 0.65 MnO 3 , where A is for the alkaline earth divalent cations ͑Ca, Ba, Sr͒, which are all characterized by the same large tolerance factor (tϭ0.934), have been investigated by using electron microscopy, electrical resistivity, magnetic susceptibility, and magnetization. It is clearly established that a transition from ferromagnetic metallic towards spin-glass insulator samples is induced as the A-site cationic size mismatch is increased. Moreover, the magnetoresistance ͑MR͒ properties of these manganites are strongly reduced for the spin-glass insulators, demonstrating that the A-site cationic disorder is detrimental for the colossal MR properties. Based on these results, a new electronic and magnetic diagram is established that shows that the A-site disorder, rather than the A-site average cationic size ͑or t͒ is the relevant factor for generating spin-glass insulating manganites. ͓S0163-1829͑99͒01746-4͔

Magnetic and magnetotransport properties of the orthorhombic perovskites(Lu,Ca)MnO3

“…The magnitude of 2 is believed to correlate with the appearance of the SG insulator state such that the larger the 2 value is the more favored the SG insulator state is. 32,33 Our finding of a SG insulator state for ͑Lu 0.7 Ca 0.3 ͒MnO 3 is in agreement with its large 2 value of 4.29ϫ 10 −3 Å 2 , which is much larger than that of ͑Dy 0.7 Ca 0.3 ͒MnO 3 ͑1.82ϫ 10 −3 Å 2 ͒ without a cusp in its Ј-T curve. 33 We thus conclude that the local structural changes induced by the large size mismatch between the cations, Lu III and Ca II , and the strongly distorted crystal structure most likely cause the magnetic competition in ͑Lu, Ca͒MnO 3 .…”

Magnetic relaxation inLa0.250Pr0.375Ca0.375Deac1, Diaz2, Kim3 et al. 2002Phys. Rev. B676380View full textAdd to dashboardCite

“…Indeed logarithmic time dependence has been observed in the relaxation of both resistivity and magnetization after sudden changes in magnetic field [7,8,9,10,11,12,13,14,15,16,17], and there have been numerous reports of spinglass-like behavior in these materials [18,19,20,21,22] (although the qualitative details of the behavior are not necessarily consistent with the conventional behavior of spin glasses [23]). While this sort of glassy behavior and the slow relaxation can be attributed to domains in ferromagnets, to superparamagnetism or to conventional spin glass phases associated with local disorder, another possibility in the phase separated materials is that the relative fractions of the different phases slowly adjust to changes in the external environment.…”

Magnetic and electronic ground states of B-site-substituted LaMnO3: from antiferromagnetism to ferromagnetism

“…Figure 3 also shows the influence of the frequency of the AC magnetic field on the magnetic susceptibility. This is often parameterised by the quantity K = ∆T p /(T p ∆(log f)), where T p is the peak temperature and f the frequency of the AC magnetic field [34]. In the case of LaMnO 3 , the variation is not significant.…”