Frustrated states of the spin-glass type in diluted ferrimagnetic oxides

Abstract

The results of comprehensive experimental research on two model frustrated systems of dilute ferrimagnetic oxides—the slightly anisotropic cubic spinels Li0.5Fe2.5−xGaxO4 and the highly anisotropic hexagonal BaFe12−xGaxO19—are reviewed and summarized. The concentration x-T phase diagrams constructed for this class of magnets for the first time are discussed, the mechanisms of formation of disordered states of the spin-glass type (with the role of the exchange interaction and anisotropy taken into account) are examined, and the structure of the states and the influence of spatial inhomogeneity of the cluster type are considered. It is shown for the example of the Li–Ga spinels that in this class of anisotropic Heisenberg magnets with short-range exchange the form of the x-T diagram differs from the canonical form for spin-glass systems: in the reentrant region (0.9⩽x⩽1.5) one observes a new cooperative frustrated state and a line of first-order phase transitions T1(x) terminating in a critical point at x=0.8.

Intrinsic exchange bias inZnxMn3−xO4Shoemaker1, Rodriguez2, Seshadri3 et al. 2009Phys. Rev. B323250View full textAdd to dashboardCite

“…The T f versus H 2/3 dependence plotted in Fig. 11 indicates excellent agreement with de Almeida-Thouless (AT) behavior, 47 which is typical not only for bulk frustrated and dilute spin glasses, 48 but also for a wide variety of systems with disordered spins at surfaces and interfaces. 7,8,49 No such behavior is seen in the x = 0.25 sample, since the Mn spins now occupy 75 % of the A-sites and the ferrimagnetic phase has effectively percolated the entire structure.…”

Reentrant spin-glass behaviour in highly frustrated Mn-rich spinel zinc manganate

“…Conversely, rise in zinc content would destroy spin glass ordering as evident in Zn 0.75 Mn 2.5 O 4 [8] and pristine ZnMn 2 O 4 [6]. It is worth noting that T f < T C , which means that glassy transition occurs after traversing ferrimagnetic long-range ordering from which we suggest that Zn 0.67 Mn 2.33 O 4 reveals re-entrant spin-glass like behaviour [16]. Such a low-temperature re-entrant spin-glass transition must be the result of competing exchange interaction between antiferromagnetic and ferrimagnetic regions among Mn 2+ and Zn 2+ ions in the (Zn x Mn 1−x )Mn 2 O 4 matrix.…”

“…In general, the magnetic properties are highly influenced by the compositional changes of the geometrically frustrated systems [10][11][12][13][14][15]. Especially, a phenomenon like spin-glass state often emerges owing to the magnetic dilution as the result of the participation of diamagnetic ions or competing exchange interactions (in case of magnetic ions) depending on their percolation threshold [8,13,16]. According to Villain [17], percolation threshold (p c ) plays a vital role to decide the contribution of long-range magnetic ordering and short-range interactions.…”

“…Even though it has been reported on many spinel based systems including CoCr [13,15,16,20,21], very few reports are available for the manganate based spinel oxides [8,11]. As explained previously, Shoemaker et al [8] and Nadherny et al [9] observed that the exchange bias was prominent (x = 0.3) at lower concentrations of Zn (0 < x < 0.5) and the emergence of spin-glass state at higher concentration of Zn (0.5 ≤ x < 1) in their Zn x Mn 1−x Mn 2 O 4 system.…”