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Engineering Magnetic and Tunneling Magnetoresistance Properties of Co x Fe 3−x O 4 Nanorods
Author(s) -
Mitra Arijit,
Mohapatra Jeotikanta,
Sharma Himanshu,
Aslam Mohammed
Publication year - 2017
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201700505
Subject(s) - nanorod , coercivity , materials science , magnetoresistance , curie temperature , paramagnetism , remanence , magnetocrystalline anisotropy , oleylamine , magnetization , condensed matter physics , ferromagnetism , magnetic anisotropy , analytical chemistry (journal) , nanotechnology , magnetic field , chemistry , nanoparticle , chromatography , physics , quantum mechanics
A simple cation exchange reaction has been adapted to produce the Co x Fe 3−x O 4 nanorods with different concentration of Co. The substitution of Fe 2+ with Co 2+ ions increase the magnetocrystalline anisotropy and coercivity of pristine superparamagnetic Fe 3 O 4 nanorods. Atomic concentration of 5–11% of Co 2+ in Fe 3 O 4 nanorods renders coercivity of 300–460 Oe at room temperature and 2200–4050 Oe at 10 K. Hydrocarbon long‐chain amine (oleylamine) functionalized nanorod assemblies form a multiple tunnel junction, where organic amine monolayers act as insulating tunnel barriers. Co x Fe 3−x O 4 nanorods show a magnetoresistance switching behavior at room temperature and the switching field is consistent with the magnetic coercivity. A 14–15% TMR is recorded at room temperature in Co x Fe 3−x O 4 nanorod assemblies, which increases to 23–26% at 150 K at a magnetic field of ±2 T. The calculated spin polarization for Co 0.33 Fe 2.67 O 4 nanorods at room temperature is 52%. A similar spin polarization and TMR as Fe 3 O 4 in Co‐doped Fe 3 O 4 nanorod assemblies is obtained. Thus, controlled doping of Co ions engineers the coercivity and remanence of the “super‐paramagnetic” Fe 3 O 4 without hindering their TMR performances, which could be very useful for memory devices.