Low Temperature Physics: 36, 682 (2010); https://doi.org/10.1063/1.3490833 (11 pages)
Fizika Nizkikh Temperatur: Volume 36, Number 8-9 (August 2010), p. 861-874    ( to contents , go back )

Manifestation of intergranular interactions in nanogranular films of (CoFeB)x-(SiO2)1-x in temperature and angular dependences of coercivity

S.M. Ryabchenko, A.A. Timopheev, V.M. Kalita, A.F. Lozenko, P.A. Trotsenko

Institute of Physics of the National Academy of Sciences of Ukraine, 46 Nauki Ave., Kyiv 03028, Ukraine
E-mail: timopheev@iop.kiev.ua

V.A. Stephanovich

Институт математики и информатики, Опольский университет, Олеска 48, 45-052 Ополе, Польша

M. Munakata

Лаборатория энергетической электроники, университет Сойо, 860-0082, Япония
pos Анотація:

Received December 14, 2009, revised January 8, 2010

Abstract

The physically nonpercolated nanogranular films of (CoFeB)x–(SiO2)1–x with the oriented intraplane anisotropy of granules display unusual properties of temperature (4.5–550 K) and angular (in the film plane) dependences of coercive fields as compared to those caused by blocking thermoactivated reorientation of the granule magnetic moments. At temperatures above the blocking temperature Tb ≈ 350–370 K a noticeable coercivity weakly dependent on measurement duration is observed as opposed to a similar dependence at temperatures below Tb. Its angular (in the film plane) dependence differs qualitatively from that expected for the blocked superparamagnetic particles. These features are explained by the superferromagnetic ordering of the magnetic moments of granules occurred due to the interaction between them at T > Tb. With dicreasing temperature below 100 K, the coercive field Hc for magnetization in the easy direction grows substantially more, than expected for the blocked superparamagnetic ensemble. Simultaneously, there occures Hc ≠ 0 for magnetization along the hard direction in the plane. The angular (in the plane) dependence of Hc acquires two maxima, along easy and hard (in the plane) directions. The above phenomenon is explained by the manifestation of superspinglass correlations in mutual orientations of the magnetic moments of granules in the ensemble.

PACS: 61.46.–w Structure of nanoscale materials;
PACS: 75.30.Gw Magnetic anisotropy;
PACS: 75.50.Tt Fine-particle systems; nanocrystalline materials;
PACS: 75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects;
PACS: 75.60.Jk Magnetization reversal mechanisms;
PACS: 75.75.–с Magnetic properties of nanostructures.

Key words: nanogranular ferromagnetic film, superparamagnetism, superferromagnetism, superspinglass state, coercivity.

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