Magnetoresistance of Drop-Cast Film of Cobalt-Substituted Magnetite Nanocrystals

Abstract

An oleic acid-coated Fe2.7Co0.3O4 nanocrystal (NC) self-assembled film was fabricated via drop casting of colloidal particles onto a three-terminal electrode/MgO substrate. The film exhibited a large coercivity (1620 Oe) and bifurcation of the zero-field-cooled and field-cooled magnetizations at 300 K. At 10 K, the film exhibited both a Coulomb blockade due to single electron charging as well as a magnetoresistance of ∼-80% due to spin-dependent electron tunneling. At 300 K, the film also showed a magnetoresistance of ∼-80% due to hopping of spin-polarized electrons. Enhanced magnetic coupling between adjacent NCs and the large coercivity resulted in a large spin-polarized current flow even at 300 K.

Field Effect of a Chemically Assembled Fe3O4 Nanocrystal Film Single‐Electron Transistor

“…While we synthesized magnetite NCs at 573 K in our previous works, [6][7][8] in this work we lowered the synthesis temperature by 35 K to improve NC size-controllability. [18] By refluxing at 538 K for 30 min, Fe 3 O 4 NCs were synthesized from a solution of tris(2,4-pentanedionato)iron(III), phenyl ether, oleic acid, oleylamine, and 1,2-hexadecanediol in a 2:127:6:6:10 molar ratio.…”

“…Single‐electron transistors composed of Fe 3 O 4 NCs are of great interest, as novel transport properties are expected due to the field effect on spin‐dependent, single‐electron transport. We previously reported a large negative magnetoresistance (MR) for NC arrays of Fe 3 O 4 and its analogs, which encouraged us to develop two‐terminal, spin‐polarized current switching devices . The source‐drain current ( I ) of a single‐electron transistor constructed of isolated Fe 3 O 4 NCs depends not only on the bias voltage ( V ) but also on the gate voltage ( V G ).…”

“…In multiple‐junction systems of isolated Fe 3 O 4 NCs, parallel magnetic configurations enlarge, and antiparallel magnetic configurations suppress, the probability of spin‐polarized electron transport between adjacent NCs. Differential resistance is low in a non‐zero field ( H ≠ 0) and high in a zero field ( H = 0), resulting in a large, negative MR for assemblies of oleic acid‐coated NCs of Fe 3 O 4 and its analogs . Single‐electron tunneling (the Coulomb staircase) at room‐temperature has been reported for carboxylic acid, monolayer‐coated nanoparticles of Fe 3 O 4 with an outer layer of Fe 2 O 3…”

“…We previously reported a large negative magnetoresistance (MR) for NC arrays of Fe 3 O 4 and its analogs, which encouraged us to develop two-terminal, spin-polarized current switching devices. [6][7][8] The source-drain current (I) of a single-electron transistor constructed of isolated Fe 3 O 4 NCs depends not only on the bias voltage (V) but also on the gate voltage (V G ). In such a device, the ferromagnetic coupling between adjacent NCs due to an applied magnetic field (H) enlarges I at any V, and simple tuning of the energy level splitting in each NC by V G further multiplies the I value.…”

“…Differential resistance is low in a nonzero field (H 6 ¼ 0) and high in a zero field (H ¼ 0), resulting in a large, negative MR for assemblies of oleic acid-coated NCs of Fe 3 O 4 and its analogs. [6][7][8] Single-electron tunneling (the Coulomb staircase) at room-temperature has been reported for carboxylic acid, monolayer-coated nanoparticles of Fe 3 O 4 with an outer layer of Fe 2 O 3 . [12] Suppression of I flow via isolation of the NCs between sourcedrain electrodes is known as a Coulomb blockade, which originates from the charging energy (E c ) of the NCs due to their small capacitance:…”