Size and Crystallinity Dependence of Magnetism in Nanoscale Iron Boride, α-FeB

Abstract

A nanoscale boride, α-FeB, with grains of variable size and crystallinity was synthesized by precipitation from solution followed by heat treatment (450 °C, 550 °C, 750 °C, 1050 °C). Analysis of transmission electron micrographs, electron diffraction, and magnetic measurements suggests superparamagnetism at room temperature for the smaller, more disordered particles of FeB, while the larger, more crystalline particles of α-FeB, with a particle size of approximately 20 nm, display open magnetic hysteresis loops and blocking. In contrast to the soft ferromagnetism of bulk β-FeB, which was synthesized by conventional solid state reaction at 1500 °C, the sample of α-FeB annealed at 1050 °C is a harder ferromagnet, possibly due to stacking faults that pin the magnetic domains; these stacking faults are apparent in the high resolution transmission electron micrographs. The changes in magnetic behavior are visible from the varying blocking temperatures (63 K, 94 K, 150 K, and >320 K from the smallest to the largest particles) and correlate with the transformations from amorphous to α-FeB and from α-FeB to β-FeB.

Efficient water oxidation with amorphous transition metal boride catalysts synthesized by chemical reduction of metal nitrate salts at room temperature

“…The texture of the amorphous samples with higher Fe content looks more like iron boride nanoparticles sponge morphologies that have been reported. 31 The quaternary metal borides catalysts (Fig. 2e and f) were also precipitated as nanoparticle aggregates with similar morphologies to the Co:Fe and Ni:Fe amorphous metal borides; these morphologies are very different to the non-porous morphologies of the corresponding crystalline perovskites Ba 5 (Fig.…”

Synthesis of a Highly Efficient Oxygen‐Evolution Electrocatalyst by Incorporation of Iron into Nanoscale Cobalt Borides

“…[7] The Fe ions were described to be the active centers, with aC oOOH matrix stabilizingt he catalysti na lkalinee lectrolytes. [51][52][53] However,t oo ur knowledge,t his is the first report on the production of crystalline (compare to Ref. Herein, mixed-metal boridesa re shown to be competitivew ith established electrocatalysts like noble metal oxides and other transition-metal(oxide)-based catalysts.…”

“…The principle of precipitation of boridesi ns olvents using reducing agents has been described as early as 1953, [47][48][49][50] and the method has recently been extended to produce new nanoscale materials with specific structuresa nd properties. [51][52][53] However,t oo ur knowledge,t his is the first report on the production of crystalline (compare to Ref. [54] for amorphous alloys) mixed-metal borides by bottom-up synthesis in solvents at low temperatures followed by annealing at moderate temperatures.C ontrary to conventional (hightemperature) routes for boride synthesis, the low-temperature solution yields powders that are highly reactive.…”

A Simple, General Synthetic Route toward Nanoscale Transition Metal Borides

“…Metal borides constitute a class of materials that are still exotic to most chemists and material scientists, despite some excellent properties that have led to some key industrial applications such as hard magnets (Nd 2 Fe 14 B), superconductors (MgB 2 ), bulk refractory and conductive ceramics (ZrB 2 , HfB 2 ), and hard materials (TiB 2 ) . Also, several other properties of bulk metal borides have been the focus of many recent investigations, these include super hardness, thermoelectric and magnetic properties, materials for batteries, and catalysts . Transition metal boride materials have attracted considerable attention in recent years.…”

“…Therefore, the search for new synthetic strategies toward single‐phase crystalline transition metal boride remains a hot topic. Other synthetic methods have been also recently attempted for micro‐ and nanoscale metal borides, such as metal flux synthesis (Al and Sn), wet‐chemical synthesis, borohydride reduction, and inorganic molten salt approach, but none of them has been successful in terms of generalization of transition metal synthesis . Hence, the development of a general route for the synthesis of crystalline transition metal boride nanomaterials with well‐defined morphology and small particle sizes is highly desirable but very challenging.…”