High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect.
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 (T(B)<70  K) become magnetically stable above 400 K when embedded in a high-Néel-temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable T(B) enhancement is due to a magnetic proximity effect between a thin CoO shell (with low Néel temperature, T(N), and high anisotropy, K(AFM)) surrounding the Co nanoparticles and the NiO matrix (with high T(N) but low K(AFM)). This proximity effect yields an effective antiferromagnet with an apparent T(N) 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 T(B) increase. Mean-field calculations provide a semiquantitative understanding of this magnetic-proximity stabilization mechanism.
Instituto Regional de Investigación Científica Aplicada (IRICA) and Departamento de Física Aplicada, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain.
José A
JA
De Toro
Instituto Regional de Investigación Científica Aplicada (IRICA) and Departamento de Física Aplicada, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain.
Daniel P
DP
Marques
Instituto Regional de Investigación Científica Aplicada (IRICA) and Departamento de Física Aplicada, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain.
Pablo
P
Muñiz
Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain.|Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.
Vassil
V
Skumryev
Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain.|Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.
Jordi
J
Sort
Université Grenoble Alpes, Institut NEEL, F-38042 Grenoble, France.|CNRS, Institut NEEL, F-38042 Grenoble, France.|Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, 21941-972, Brasil.
Dominique
D
Givord
Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.|ICN2-Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, E-08193 Bellaterra, Barcelona, Spain.
Josep
J
Nogués