TY - JOUR
T1 - High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect
AU - De Toro, José A.
AU - Marques, Daniel P.
AU - Muñiz, Pablo
AU - Skumryev, Vassil
AU - Sort, Jordi
AU - Givord, Dominique
AU - Nogués, Josep
PY - 2015/7/28
Y1 - 2015/7/28
N2 - © 2015 American Physical Society. Thermal activation tends to destroy the magnetic stability of small magnetic nanoparticles, with crucial implications for ultrahigh density recording among other applications. Here we demonstrate that low-blocking-temperature ferromagnetic (FM) Co nanoparticles (TB<70K) become magnetically stable above 400 K when embedded in a high-Néel-temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable TB enhancement is due to a magnetic proximity effect between a thin CoO shell (with low Néel temperature, TN, and high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix (with high TN but low KAFM). This proximity effect yields an effective antiferromagnet with an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations via core-shell exchange-bias coupling, leading to the observed TB increase. Mean-field calculations provide a semiquantitative understanding of this magnetic-proximity stabilization mechanism.
AB - © 2015 American Physical Society. Thermal activation tends to destroy the magnetic stability of small magnetic nanoparticles, with crucial implications for ultrahigh density recording among other applications. Here we demonstrate that low-blocking-temperature ferromagnetic (FM) Co nanoparticles (TB<70K) become magnetically stable above 400 K when embedded in a high-Néel-temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable TB enhancement is due to a magnetic proximity effect between a thin CoO shell (with low Néel temperature, TN, and high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix (with high TN but low KAFM). This proximity effect yields an effective antiferromagnet with an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations via core-shell exchange-bias coupling, leading to the observed TB increase. Mean-field calculations provide a semiquantitative understanding of this magnetic-proximity stabilization mechanism.
U2 - 10.1103/PhysRevLett.115.057201
DO - 10.1103/PhysRevLett.115.057201
M3 - Article
SN - 0031-9007
VL - 115
JO - Physical Review Letters
JF - Physical Review Letters
M1 - 057201
ER -