Reentrant superspin glass state and magnetization steps in the oxyborate Co2AlBO5

Abstract

An oxyborate Co2AlBO5 belonging to the ludwigite family is investigated using structural, thermodynamic, dielectric and magnetic measurements. Magnetic measurements indicate that this system is seen to exhibit long range magnetic ordering at T N = 42 K, signatures of which are also seen in the specific heat, dielectric susceptibility, and the lattice parameters. The absence of a structural phase transition down to the lowest measured temperatures, distinguishes it from the more extensively investigated Fe-based ludwigites. At low temperatures, the system is seen to stabilize in a reentrant superspin glass phase at T G = 10.6 K from within the magnetically ordered state. This ground state is also characterized by magnetic field induced metamagnetic transitions, which at the lowest measured temperatures exhibit a number of sharp magnetization steps, reminiscent of that observed in the mixed valent manganites.

Unconventional superparamagnetic behavior in the modified cubic spinel compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$

“…( 29) resulting E a /k B 61.7 K and τ 0 3.7 × 10 −6 s. Such an Arrhenius behaviour is often considered to be the characteristic feature of superparamagnetism. [69] The value of τ 0 is also seems to be within range expected for superparamagnets (10 −6 to 10 −9 s) [70].…”

Investigations of the heterometallic ludwigite Ni2AlBO5

“…In contrast, the M H isotherms as measured in Ni 2 AlBO 5 is in line with that expected for a normal antiferromagnetic specimen, as is seen in Figure 3c. Though a meta-magnetic transition is seen at about 2 Tesla, this transition appears to be associated with a routine (spin flop like) rotation of the antiferromagnetic sublattice magnetization as a function of the applied field [16]. Incidentally, the homometallic Fe 3 BO 5 ludwigite was reported to exhibit a structural transition around room temperature due to the charge ordering of Fe 2+ ions [2].…”

Antiferromagnetism of the cation-ordered warwickite system Mn2-Mg BO4 (x = 0.5, 0.6 and 0.7)

“…The fact that the octahedral site cation ordering is influenced by the ordering of the local distortions is confirmed by the similar analysis performed for the homometallic compounds (they are also shown in Figs. 16). For V2BO4, only the room-temperature crystal structure data are available in the literature [23].…”

“…Recently, a significant attention has been devoted to complex oxyborates that are isostructural to ludwigite and warwickite minerals [14][15][16]. The general formula of these compounds is M 2+ nM 3+ OnBO3, where n = 1 for the warwickites and n = 2 for the ludwigites.…”