Magnetic properties of nanoclusters formed by implantation of Fe into Ge using a metal-vapor vacuum arc ion source

Abstract

The magnetic properties of Fe ions implanted into a germanium crystal by metal-vapor vacuum arc ion source were investigated using a Quantum Design SQUID magnetometer. The presence of Fe nanoclusters in Ge was verified by magnetization measurements. A Langevin fit was used to obtain the size distribution of the clusters. The results demonstrated that the clusters are magnetic. The magnetic behavior of the clusters was characterized by zero-field-cooled and field-cooled measurements for temperatures 4.2 to 300 K. The implanted layer with magnetic clusters shows negative magnetoresistance with a positive magnetoresistance background due to the Ge substrate for parallel magnetic-field geometry at temperatures 180 to 300 K. The negative magnetoresistance is found to become dominant with decrease of temperature. The negative magnetoresistance is attributed to the existence of magnetic clusters in the implanted layer.

Synthesis of Highly Crystalline and Monodisperse Cobalt Ferrite Nanocrystals

“…(1) ZFC magnetization (M ZFC ) increased as the temperature increased from 5 K and reached a maximum at the blocking temperature (T B ) and then decreased; (2) FC magnetization (M FC ) steadily decreased as temperature increased from 5 K; (3) M ZFC and M FC overlapped at temperatures over the corresponding T B . 3a, [8][9][10] The difference between M ZFC and M FC below T B mainly resulted from the existence of energy barriers of magnetic anisotropy. The total magnetic anisotropy constant (K) of magnetic nanocrystals can be determined using the equation K ) 25k b T B /〈V〉, where k b is the Boltzman constant and 〈V〉 is the median volume of a single nanocrystal.…”

“…A total of 0.2 g of (η 5 -C 5 H 5 )CoFe 2 (CO) 9 (1.23 mmol; total metal atoms) was added to a mixture containing 5 mL of dioctyl ether, 0.35 g of oleic acid (1.23 mmol) and 0.49 g of lauric acid (2.46 mmol) at room temperature under an argon atmosphere. The rest of the synthetic procedure is very similar to the one applied for the synthesis of 6 nm cobalt ferrite nanocrystals.…”

“…7 A typical synthesis of cobalt ferrite nanocrystals with a particle diameter of 6 nm is as follows. A total of 0.2 g of (η 5 -C 5 H 5 )-CoFe 2 (CO) 9 (1.23 mmol; total metal atoms) was added to a mixture containing 5 mL of dioctyl ether and 1.04 g of oleic acid (3.69 mmol) at room temperature under an argon atmosphere. The mixture was heated to reflux (∼300°C) and kept at that temperature for 1 h. The color of the reaction mixture changed to clear blue at 230°C and to black at the reflux temperature.…”

“…When the starting reaction mixtures containing the stabilizing agents and the precursor at the molar ratios of 1:1 and 1:5 were applied in the synthesis, cobalt ferrite nanocrystals with particle sizes of 4 and 8 nm were obtained, respectively (Supporting Information). To synthesize 4 nm nanocrystals, 0.2 g of (η 5 -C 5 H 5 )CoFe 2 (CO) 9 (1.23 mmol; total metal atoms) was used with 0.17 g of oleic acid (0.615 mmol) and 0.15 g of hexadecylamine (0.615 mmol). The mixture was refluxed in dioctyl ether and oxidized.…”

“…The precursor, (η 5 -C 5 H 5 )CoFe 2 (CO) 9 , was prepared using the previously reported synthetic procedure. 7 A typical synthesis of cobalt ferrite nanocrystals with a particle diameter of 6 nm is as follows.…”