Dimensional crossover in magnetic warwickites

Abstract

We present an investigation of the magnetic properties of a series of warwickites with different transition metals. These materials are characterized by one-dimensional structures called ribbons where the transition metals are randomly located. The present results allow for a systematic investigation of the hierarchy of magnetic interactions in these systems. While the intraribbon interactions are mainly direct d-d interactions between the transition-metal ions, the interribbon interaction is due to superexchange between metals in different octahedra mediated by the oxygen in the common corner. ͓S0163-1829͑97͒00625-5͔

Spin-glass behavior in single crystals of hetero-metallic magnetic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4

“…Quantum entanglement appears at temperatures in between T SG and about T E ¼ 130 K, confirming the existence of random magnetic chains, as in other heterometallic warwickite compounds [9][10][11][12][13][14]. At high temperatures (T 4T E ), these systems follow a Curie-Weiss law with AF interactions.…”

“…The exponent is similar for the pure compounds, α¼0.62 and 0.63 for Mg-Fe and Co-Fe respectively, and lower for the mixed warwickite, 0.45. In a previous work [12] they obtain α¼ 0.54 for MgFe warwickite, although this value depends on the fitted temperature range. Similar values of α have been found in the S¼ 1/2 MgTiOBO 3 warwickite, where a further analysis allows to quantify quantum entanglement in this low-dimensional spin system [11].…”

“…At present there are reports on only two homo-metallic (M ¼M′) warwickites: Fe 2 BO 4 [2][3][4][5][6] and Mn 2 BO 4 [4,[6][7][8], exhibiting both long-range magnetic order. Several studies have been done on different magnetic properties of heterometallic (M≠M′) warwickites with only one magnetic ion, MgTiBO 4 [9][10][11], MgCrBO 4 [12], MgFeBO 4 [12,13], NiScBO 4 [12], MnScBO 4 [12], MgVBO 4 [12,14].…”

Magnetic interactions in the monoclinic ludwigite Cu FeO BO

“…As for the warwickite MgFeOBO 3 [2] the distribution centered at about 100 KOe is attributed to decoupled iron. This contribution is present even at low temperatures such as 4.2 K (Fig.…”

“…One of the main intriguing problems related to the oxyborates is to understand how the low dimensionality they present, determines their magnetic and electric behavior. For the purpose of understanding such inter-relation we carried out a detailed study on several magnetic warwickites which constitute another well known structure of the oxyborate family [1][2][3]. The structure of these systems can be viewed as an assembling of sub-units, in the form of ribbons, where the magnetic ions are randomly located.…”