Arrangement of FePt Nanocubes Utilizing Chemical Binding Selectivity

Abstract

This study on future ultrahigh density magnetic recording devices aims to develop a technique for arranging FePt nanocubes on a substrate by using organosilane as an interlayer. An array of FePt nanocubes was formed by chemical synthesis, utilizing the Pt-S binding between the SH functional group in ͑3-mercaptopropyl͒trimethoxysilane and Pt in the FePt nanocubes. The morphology of the FePt nanocube array on the substrate was characterized using atomic force microscopy and plan-view scanning electron microscopy, which revealed that the array was a monolayer. After SiO 2 was coated by chemical vapor deposition as a protective layer for sintering prevention, annealing was carried out at 900°C for 3 h in a reducing atmosphere to transform the crystal structure of the FePt nanocubes to the L1 0 phase. X-ray diffraction results revealed that the annealed FePt nanocube array had a FePt͑110͒ orientation and L1 0 phases such as ͑001͒ and ͑110͒. The Pt-S binding did not obstruct the L1 0 ordering of FePt. Consequently, a method for arranging nanoparticles by using the organic molecules with functional groups that can interact with nanoparticle selectivity as an interlayer can be applied as a formation technique for arranging a wide range of nanoparticles. L1 0 -FePt alloys have a very high uniaxial magnetic crystalline anisotropy energy ͑K u = 7 ϫ 10 7 erg/cm 3 ͒. Because the superparamagnetic fluctuation of room-temperature magnetization can be suppressed even for grains with a diameter of 3.0 nm, the appropriate arrangement of FePt nanoparticles composed of one recording bit ϫ one particle is a promising candidate for next-generation-type ultrahigh density magnetic recording media with capacities of Ͼ10 Tbit in. −2 . Since the preparation of monodisperse FePt nanoparticles by chemical synthesis was reported by Sun et al., 1-4 many researchers have paid attention to such nanoparticles for a wide range of applications including magnetic recording media, 5-8 ferrofluids, 9-11 magnetic hyperthermia, 12 magnetic resonance imaging contrast agents, 13 magnetic cell separation, 14 and environmental remediation. 15 Techniques for arranging nanoparticles and controlling the magnetic easy axis in two dimensions ͑2D͒ are very important for the development of ultrahigh density magnetic recording media. Some methods of 2D arrangement such as self-organization and Langmuir-Blodgett ͑LB͒ 16-19 have been reported. It is difficult to use the self-assembly and LB techniques for controlling better organized monolayers on a substrate. This study aims to develop a technique for arranging FePt nanoparticles on a substrate by using organosilane as an interlayer. Previously, we succeeded in fabricating cubic FePt nanoparticles ͑FePt nanocubes͒ with partial L1 0 phases by controlling the growth temperature during chemical synthesis. 20 Self-assembled FePt nanocubes have a ͑100͒ texture on a Cu grid with a carbon-supporting film. This shape-controlled synthesis and self-assembly offers a promising approach to fabricate magnetically aligned FePt na...

(Invited) Development on Self-Assembly Technique for Arrangement of Chemically Synthesized FePt Nanoparticles

“…For application as-synthesized FePt nanoparticles to BPM, we attempted to develop a simple process to control the distortion of the FePt array using chemical synthesis and geometrical grid prepared by ultraviolet nanoimprint lithography (UV-NIL). Previously, we succeeded in the fabrication of cubic FePt nanoparticles by controlling the reaction temperature in chemical synthesis; the FePt nanoparticles were immobilized by using chemical bonding on a thermal oxide Si substrate with modified (3-mercaptopropyl)trimethoxysilane, MPTMS as an interlayer between the FePt nanoparticles and the Si(100) substrate (14,15). The model image is shown in Fig.…”

“…However, the arrangement of the FePt nanoparticles formed irregularities, laminate structures, and aggregates (shown in Fig. 5) (15). In this section, the hole patterns of 200 nm width, 40 nm depth and 500 nm pitch were used as the geometrical grid on Si(100), and FePt-distributed solution was coated on the geometrical grid using a picoliter pipette (PicoPipet, Altair), which provides droplets down to 50-500 nl.…”

“…We used extreme high resolution scanning electron microscopic (XHR-SEM) imaging to show that the FePt nanoparticles were successfully arranged as a single layer with the with the average pitch of 10.0 nm by chemical bonding between Pt in the FePt particle and SH in MPTMS on the geometrical grid of Si(100) (shown in Fig. 6) (16)(17)(18). Based on our results, the selfassembly array of the FePt nanoparticles are considered to be formed by the following process; 1.…”

Influence of Cu on the Improvement of Magnetic Properties and Structure of L10 FePt Nanoparticles

“…Since the pioneering work of Sun et al, the size and morphology control of FePt NPs have been extensively studied. FePt nanorods [ 15 , 16 ], nanowires [ 17 , 18 ], nano-cubes [ 19 ], and coral-shaped [ 20 , 21 ] NPs of the fcc phase have been successfully prepared. However, FePt NPs with fcc phase show low magneto-crystal anisotropy and soft magnetic or superparamagnetic at room temperature which greatly limits their applications.…”

Fe50Pt50/Fe2Pt98Magnetic Multilayers Electrodeposited from Ionic Liquids

“…[13][14][15] However, hydrogen evolution during electrodeposition in the aqueous electroplating solutions can influence the structure and properties of FePt thin films. 2,16 To avoid the above disadvantages, ionic liquid are considered ideal solvents and chelate complex because of wide electrochemical window, undetectable vapor pressure, and good organic and inorganic compound solubility. Additionally, hydrogen evolution can be significantly suppressed when dry aprotic ionic liquid are employed.…”