MAGNETISM OF RANDOMLY CANTED Li-Ti FERRITE

Abstract

FC-ZFC magnetisation, hysteresis, thermoremanence and neutron diffraction measurements were performed on Li1.125Feo.625Ti1.2504. The results are interpreted from domain and wall properties resulting of local canted state where the spin transverse component relaxes between preferential directions.

Magnetic structures in substituted ferrites

“…These irreversibilities are strongly field dependent in the whole temperature range below TN and disappear at medium fields. Moreover the coercive field is small below T N , as in ferrimagnets, but increases strongly at low temperatures where both S, freezing and hysteresis loop time dependence are observed [32,33]. In figure 6, we have represented firstly the field dependence of the branching point T ( K l temperature of ZFC and FC magnetisation curves and secondly the temperature dependence of the field at which the hysteresis loop closes, in the case of an A15 compound with x = 1.25 [32,33].…”

“…ForthesystemsA21 [41],A31withx = 0.8and1[14,43], A32 [45] and A51 withx s 0.85 [49], the absence of long-range order magnetic lines and the existence of a developed short-range order hump peaking indicate spin-glass or spinglass-like properties. In the case of systems A13 with x = 0.66 [27], A15 with x = 1.1 and 1.32 [32], B21 with x = 0.5 and 0.75 [57] and B31 with x = 0.4 and 0.8 [60], the existence of a magnetic contribution in the neutron lines indicates long-range ferrimagnetic ordering. The absence of a sharp (200) magnetic reflection and the fact that the deduced magnetic moment (at least for one site) is clearly lower than the expected values from a collinear structure are in favour of the LCS structure.…”

“…There are also some properties which, at first sight, appear characteristic of spin-glass-like or cluster glass phases but which are not in reality a proof. Only two systems have been the object of detailed studies: the A15 [32,33] and A51 [49] systems. Only the first is representative of a two-sublattice system.…”

“…Only in the A31 system has a stretched exponential law been observed [43]. In the A15 system with x = 1.25 [32,33], the remanent magnetisation and thermoremanence exhibit two regimes: one for temperatures above 15 K and the other for temperatures below 15 K. The activation energy is the sum of two terms of which one is inversely proportional to the relaxation time of the transverse spin component. In our opinion these properties can be explained in terms of the complex structure of domains and domain walls due to LCSS.…”

“…The energy required to move the walls is important as the energy barrier between energy minima is high. In fact, after spin rotation, S, is not in a direction which minimises the energy and therefore the system relaxes [32,33]. At high temperatures, the energy barrier is low and S, relaxation is rapid.…”