Decomposition of crystalline ferromagnetic particles precipitated in amorphous paramagnetic Ni-P

Abstract

According to small-angle x-ray scattering, amorphous Ni-P contains some volume per cent of metal-rich precipitations. During annealing, their diameters grow from about 2 nm in the as-prepared state to about 6 nm. It is shown by magnetic measurements that the inclusions are ferromagnetic single-domain particles embedded in a paramagnetic matrix. At sufficiently high temperatures such systems behave like superparamagnets. At 4.2 K, thermal agitation is too weak to flip the elementary magnetic moments. In this case, magnetisation curves can allow us to determine the coercivities and average saturation magnetisations. Annealing induces the two quantities measured at 4.2 K to change proportional to each other. This experimental fact justifies the application of a theory developed for fine non-interacting ferromagnetic particles having a magnetic shape anisotropy. The increase in the spontaneous magnetisation is attributed to the decomposition of the inclusions. With the aid of an approximation procedure the starting value of the phosphorus content and its decrease during annealing are estimated. These results and the values derived for the shape anisotropy agree well with those obtained through small-angle x-ray scattering. The starting phosphorus concentration of the precipitations proved to be independent of their volume fraction and the average composition of the samples. The observed kinetics fit in with the assumption of an activation energy spectrum. The lower limit starts at about 1.4 e V and is shifted on annealing to higher values.

Nanocrystalline Ni–3.6 at.% P and its transformation sequence studied by atom-probe field-ion microscopy

“…In this concentration range, the average grain size decreases from about 10±15 nm to 2±4 nm [11,13,14,23]. Within an intermediate concentration range, between about 10 and 15 at.% P, nanometersized crystallites are embedded in an amorphous matrix [4,10]. Layers with about 12±13 to 20 at.% P were found to be amorphous [8,9], and may contain a small volume fraction of crystallites [10].…”

“…Within an intermediate concentration range, between about 10 and 15 at.% P, nanometersized crystallites are embedded in an amorphous matrix [4,10]. Layers with about 12±13 to 20 at.% P were found to be amorphous [8,9], and may contain a small volume fraction of crystallites [10]. Hence, there is no indication of a sharply de®ned critical P content separating nanocrystalline and amorphous alloys.…”

Effects of phosphorus content on the reaction of electroless Ni-P with Sn and crystallization of Ni-P

“…The microstructure of Ni-P is expected to vary depending on the P content: nanocrystalline for 4.6wt.%P, amorphous with some crystallites for 9wt.%P, and completely amorphous for 13 wt.%. [6][7][8][9][10] Differential scanning calorimetry (DSC) was used to study the interfacial reaction between Ni-P and Sn and the crystallization of Ni-P at a heating rate of 5°C/min in an N 2 atmosphere. Samples heated to 300°C and 450°C in the DSC were cooled down in air to room temperature, and the remaining Sn after the reaction was etched with 10vol.%HCl solution.…”

“…5-8.5wt.%P are known to be a mixture of small crystallites and an amorphous phase. 8 A transition point to an amorphous structure is not clear because Ni-P with 10.1wt.%P was reported to have 4-5-nm grains even though its electron diffraction pattern showed amorphous characteristics. 9 The crystallization temperature of a Ni-P film is also known to vary widely depending on P content: 300-450°C for 1.9-13.6wt.%P.…”

Kinetics of primary crystallization of hypoeutectic amorphous Ni–P alloy studied by in situ ASAXS and DSC

“…Magnetic and small-angle X-ray scattering (SAXS) studies suggested that the precipitating particles may contain phosphorus [26,27]. Anomalous small-angle scattering (ASAXS) and small-angle neutron scattering confirmed that the precipitating Ni particles with radius less than 2 nm contain considerable amount of P while larger particles contain less then 2 at% P [28,29].…”