Magnetism and charge order in the ladder compound Co3O2BO3

Abstract

There are two known ludwigites containing a single transition metal element, Fe 3 O 2 BO 3 and Co 3 O 2 BO 3 . The structure of these materials has low-dimensional units in the form of three-legged ladders (3LL) that confer to each of them unique magnetic and electronic properties. Fe 3 O 2 BO 3 presents a staggered charge density wave (CDW) transition in the ladders near room temperature and two magnetic transitions. It has remained a mystery why the other compound Co 3 O 2 BO 3 behaves so conventionally, with a single magnetic transition and no CDW in spite of similar structural and electronic configurations. Neutron diffraction results presented here in this system finally unravel these differences. Far from a trivial explanation, we uncover a coexistence of low and high spin Co ions in well-defined octahedral sites. Our results allow one to solve the contrasting behavior of the Fe and Co ludwigites in terms of a subtle and unique charge ordering mechanism occurring at the microscopic level of the rungs of the 3LL.

Chemical disorder reinforces magnetic order in ludwigite (Ni,Mn)3BO5 with Mn4+ inclusion

“…The exchange interaction 4-3 and 4h-2a are responsible for the interaction between the 4-2-4 and 3-1-3 three-legged ladders. The magnetic structure studies of the Fe [2,3], Co [7], Cu-Mn ludwigite showed that the magnetic structure is divided into two subsystems formed by 3LLs. In the Fe ludwigite, the magnetic moments in the subsystems are mutually orthogonal, in the Cu-Mn ludwigite, the angle between the magnetic moments of the subsystems is 60°.…”

“…Such an orientation of the magnetic moments is apparently necessary for reducing the frustrations that arise due to the geometric features of the structure. In the Co 3 BO 5 , there is one magnetic phase transition, the magnetic moments of the ions are oriented collinearly, but the trivalent cobalt passes into a low spin state with zero spin, which is also possibly required to reduce frustrations in the system [3,7].…”

Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co$_3$O$_2$BO$_3$ ludwigite

“…Particularly, the M =Fe ludwigite shows a combined chargeordering and structural phase transition at 283 K in-volving a zigzag distortion of the 424 ladders below this temperature [6][7][8][9][10]. The M =Co ludwigite, on the other hand, does not show a similar structural phase transition, and all Co 3+ ions appear to occupy only the M 4 site [11][12][13]. Additionally, there is a possible spin-state crossover of the Co 3+ ions, which are presumably in a low-spin configuration in the magnetically ordered phase (T ≤ 43 K) and in a high-spin configuration at higher temperatures (T 200 K) where the Curie-Weiss paramagnetic behavior is established [12,14,15].…”

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

“…Moreover, these materials are also of interest with regards to fundamental physics. The strong relationship between the spin, orbital and lattice degrees of freedom allows for observations of a variety of cooperative phenomena, including charge and orbital ordering, cascades of magnetic phase transitions, structural transformations accompanied by conductivity anomalies and charge density waves formation [3][4][5][6][7][8][9][10]. A number of recent studies have demonstrated the potential of borates as high capacity cathode materials for Li and Na batteries [11][12][13].…”

“…For example, M 2+ 2Fe 3+ BO5 (M 2+ = Fe or Co) shows cascade magnetic transitions associated with the magnetic ordering of two spin ladders (3-1-3 and 4-2-4) at Neel temperatures TN1 = 112 K (PM-AFM) and TN2 = 74 K (AFM-Ferri), respectively [4,5]. In Co3BO5, the Co 3+ ions exclusively filling the M4 site are in the low-spin state (d 6 , S = 0) that makes this oxyborate a ferrimagnet with TN = 42 K [5,6].…”