Untersuchungen über das Remanenzverhalten magnetischer Einbereichs‐Kollektive

In this contribution we focus on a novel way to perform and evaluate magnetization experiments on frozen ferrofluids or magnetic nanoparticles fixed in space. The basic idea is to project the behaviour of a real particle system onto a Stoner-Wohlfarth (SW) particle ensemble behaviour. Therefore first an ideal SW particle system acting as a reference system with unique particle sizes and orientation of easy axis was studied numerically by introducing a particle-particle interaction via a demagnetizing field. We have shown that for non-interacting SW particles a universal mean value rule holds that the magnetization measured after ZFC (zero field cooling) can be expressed as a mean value of the magnetization measured after PHFC and NHFC (positive and negative high field cooling) processes. Any deviation from this mean value rule is therefore due to non-SW behaviour (multidirectional anisotropy and interaction) only and can be derived from the magnetization measurements and be compared with simulations.By this new method it is possible to determine the mean value of the particle's anisotropy and the mean interaction which is expressed here as a magnetic field.We will report on experiments performed on frozen ferrofluids because these systems offer the possibility of complete thermal demagnetization after melting. In this contribution we describe experiments performed on two different frozen Co-based ferrofluids by SQUID magnetometry.

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“…Henkel [27] used this relation extensively and created the widely used Henkel plot. In subsequent papers [29] the following relation was applied:…”

Section: Summary and Discussionmentioning

confidence: 99%

“…This kind of calculation was performed by [25][26][27] using these relations. Deviations from the SW relation can be seen in the so-called Henkel plot, which neglects any thermal activation.…”

Section: Basic Considerationsmentioning

confidence: 99%

Magnetization measurements on frozen ferrofluids: an attempt to separate interaction and anisotropy influences

Michele

Hesse

Bremers

2006

J. Phys.: Condens. Matter

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“…͑2͒ is limited to noninteracting fine-particle ensembles. In the case of interactions, it is suitable to use the Henkel plot, 2,3 where M D is plotted as a function of M R and Eq. ͑2͒ yields a straight line.…”

Section: Remanence Analysismentioning

confidence: 99%

“…In a sense, important approaches such as the Preisach model, 1 Wohlfarth's remanence relation, and Henkel plots 2,3 rely on the existence of well-defined magnetic particles or grains embedded in a magnetic environment. From a practical point of view, it is necessary to distinguish between intra-granular cooperative phenomena inside a grain or particle and inter-granular cooperativity caused by interactions between particles or crystallites ͑Fig.…”

Section: Introductionmentioning

confidence: 99%

Cooperative magnetism and the Preisach model

Skomski

Sellmyer

2001

Journal of Applied Physics

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Cooperative and noncooperative magnetization processes in magnetic nanostructures are investigated. Using model calculations it is shown that the Preisach model and related approaches, such as Henkel, ⌬M , and ⌬H plots, describe magnetism on a mean-field level and cannot account for intra-and inter-granular cooperative effects. For example, the ⌬M plot of a nucleation-controlled two-domain particle gives the false impression of a positive intergranular interaction. A simple but nontrivial cooperative model, consisting of two interacting but nonequivalent particles, is used to show that cooperative effects are most pronounced for narrow switching-field distributions, i.e., for nearly rectangular loops. This is unfavorable from the point of magnetic recording, where one aims at combining narrow loops with a noncooperative local switching behavior. A general rule is that the neglect of cooperative effects leads to an overestimation of the coercivity.

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“…In fact a fitting procedure can become more refined as discribed in [9][10][11]. 2 (2002) then the whole hysteresis loop and summarize the result in a Henkel plot [13]. 7.…”

Section: Particles With Anisotropy Energymentioning

confidence: 99%

Probing Magnetism of Nanosized Single Domain Particle Systems

Hesse

Pütter

Michele

et al. 2002

phys. stat. sol. (a)

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Magnetization measurements are the "classic" experimental method to characterize systems of single domain magnetic particles. We consider such particles fixed in space so that the orientation of the magnetization vector of each particle can be influenced by an external magnetic field with respect to characteristic particle directions, i.e. easy directions in the case of anisotropy energy. The aim of this contribution is directed towards experimentalists. We will enhance the well-known idea of the "preparation" of different low temperature magnetic states (LTMS), introduce the quasi-paramagnetic state which can be reached by the PHFC (positive high field cooling) process, briefly discuss the NHFC (negative high field cooling) and other ways to reach the LTMS. Additionally, our aim is to persuade researchers to consider the susceptibility rather than the magnetization. The most interesting topic is here the pronounced susceptibility maximum which appears in a system of small single domain particles prepared in a LTMS by a PHFC process when measuring in a constant external field versus temperature. We use the susceptibility for an ideal super-paramagnet as a limiting case and consider step by step what are the influences on the susceptibility if the real particle systems exhibit magnetic anisotropy energy, particle-particle interactions and last but not least a particle size distribution.

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Untersuchungen über das Remanenzverhalten magnetischer Einbereichs‐Kollektive

Cited by 14 publications

References 6 publications

Magnetization measurements on frozen ferrofluids: an attempt to separate interaction and anisotropy influences

Magnetization measurements on frozen ferrofluids: an attempt to separate interaction and anisotropy influences

Cooperative magnetism and the Preisach model

Probing Magnetism of Nanosized Single Domain Particle Systems

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