Intrinsic and hysteresis properties of FePt nanoparticles

Abstract

This comprehensive study examines the effect of particle size and atomic ordering on the intrinsic and hysteresis properties of FePt nanoparticles embedded in a carbon matrix formed by annealing sputtered FePt/C multilayer precursors. Structural studies show a transformation from the magnetically soft to the tetragonal FePt phase dependent on the annealing conditions. The magnetic properties scale as a function of particle size. The coercivity depends, in part, on the vol % of carbon and develops with annealing as a result of increased atomic ordering. Under the right conditions a high coercivity of 34 kOe has been achieved. Remanence curves show a variation of interparticles interactions from exchange to magnetostatic with increasing vol % carbon. Time dependent measurements indicate a decrease of the activation volume converging to the actual particle size ͑determined by TEM͒ as the carbon content is increased. The potential for future magnetic recording media is discussed.

On the phenomena occurring at the interface between iron and iron–platinum thin films

“…It shows a main peak at 276 kOe and a shoulder at 304 kOe. However, the best fitting of the spectra is obtained by superimposing to a main contribution (sextet ϕ, H hf = 275 kOe, E Q = 0.04 mm/s) the following two sextets: -sextet ψ (H hf = 305 kOe, E Q = 0.00 mm/s) which can be attributed to the cubic FePt phase [6] and -sextet τ (H hf = 269 kOe, E Q = 0.29 mm/s) which can be interpreted as due to the tetragonal FePt phase [6,7]. Accordingly, a careful inspection of the corresponding XRD spectrum (Fig.…”

“…In particular, it is reasonable to assume that evaporated 57 Fe diffuses into surface regions of the FePt hard film giving raise to superparamagnetic iron (singlet α 1 ) due to its coalescence in low density regions, and 57 Fe-containing FePt particles characterized by a large grain size distribution (τ (1,2) and δ contributions). The doublet δ can be due to FePt small particles showing a superparamagnetic behaviour and the τ 1 , τ 2 components can be ascribed to FePt larger particles showing a collapsing H hf which decreases from the value typical of the tetragonal phase [7,9].…”

Composition dependence of the coercivity in magnetic nanoparticles suitable for magnetic hyperthermia

“…They attract much attention as a promising material for hyperthermia [27][28][29]. With decreasing particle size in FePt nanoparticles C T [30,31] and c H [30] decrease. The Curie temperature of 4 nm FePt nanoparticles is about 200-300 K lower than that of bulk FePt (750 K) [31].…”

Magnetic properties and L1 phase formation of FePt films prepared by high current-density ion-beam irradiation and rapid thermal annealing methods

“…In order to achieve these requirements, several studies were reported. [6][7][8][9][10][11][12][13] For example, a small grain and a high perpendicular magnetic anisotropy L1 0 phase has been observed on FePt films using multilayer deposition techniques and a rapid thermal annealing ͑RTA͒ method. In general, an annealing temperature of about 350-550°C is required.…”

“…In general, an annealing temperature of about 350-550°C is required. [10][11][12][13][14] Ion-irradiation has been applied widely to modify the magnetic properties in magnetic thin films or superlattices. He-ion irradiation was used to control the degree of chemical ordering of FePd, Co/ Pt, and FePt films.…”