Structure and Magnetic Properties of L10-Ordered Fe–Pt Alloys and Nanoparticles

Lyubina, Julia; Rellinghaus, Bernd; Gutfleisch, Oliver; Albrecht, Manfred

doi:10.1016/b978-0-444-53780-5.00005-3

Cited by 49 publications

(41 citation statements)

References 334 publications

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“…As such, the L1 0 phase of iron-platinum alloys has been identified as a promising candidate as it exhibits ferromagnetism down to very small particle sizes. [236] Several techniques to prepare such arrays have been demonstrated and were introduced in chapter 3.4. They can roughly be divided into processes that use nanoscale patterning methods to create masks that are subsequently used to pattern the desired material and processes that take advantage of precursor materials that are transformed into the respective metal or metal alloy.…”

Section: Introductionmentioning

confidence: 99%

Surface Patterning with Colloidal Monolayers

Vogel

2012

Springer Theses

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This thesis focuses on the controlled assembly of monodisperse polymer colloids into ordered two-dimensional arrangements. These assemblies, commonly referred to as colloidal monolayers, are subsequently used as masks for the generation of arrays of complex metal nanostructures on solid substrates.The motivation of the research presented here is twofold. First, monolayer crystallization methods were developed to simplify the assembly of colloids and to produce more complex arrangements of colloids in a precise way. Second, various approaches to colloidal lithography are designed with the aim to include novel features or functions to arrays of metal nanostructures.The air/water interface was exploited for the crystallization of colloidal monolayer architectures as it combines a two-dimensional confinement with a high lateral mobility of the colloids that is beneficial for the creation of high long range order. A direct assembly of colloids is presented that provides a cheap, fast and conceptually simple methodology for the preparation of ordered colloidal monolayers. The produced two-dimensional crystals can be transformed into nonclose-packed architectures by a plasma-induced size reduction step, thus providing valuable masks for more sophisticated lithographic processes. Finally, the controlled co-assembly of binary colloidal crystals with defined stoichiometries on a Langmuir trough is introduced and characterized with respect to accessible configurations and size ratios.Several approaches to lithography are presented that aim at introducing different features to colloidal lithography. First, using metal-complex containing latex particles, the synthesis of which is described as well, symmetric arrays of metal nanoparticles can be created by controlled combustion of the organic material of the colloids. The process does not feature an inherent limit in nanoparticle size and is able to produce complex materials as will be demonstrated for FePt alloy particles. Precise control over both size and spacing of the particle array is presented.Second, two lithographic processes are introduced to create sophisticated nanoparticle dimer units consisting of two crescent shaped nanostructures in close proximity; essentially by using a single colloid as mask to generate two structures simultaneously. Strong coupling processes of the parental plasmon resonances of the two objects are observed that are accompanied by high near-field enhancements. A plasmon hybridization model is elaborated to explain all polarization dependent shifts of the resonance positions. Last, a technique to produce laterally patterned, ultra-flat substrates without surface topographies by embedding gold nanoparticles in a silicon dioxide matrix is applied to construct robust and re-usable sensing architectures and to introduce an approach for the nanoscale patterning of solid supported lipid bilayer membranes.

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Section: Introductionmentioning

confidence: 99%

Surface Patterning with Colloidal Monolayers

Vogel

2012

Springer Theses

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“…In particular, it is known that the magnetic properties of nanoparticles depend on the size, shape and the way of synthesizing. 11 Gas-phase particles can in fact exhibit lower MCA than perfectly-ordered bulk L1 0 alloys, because (i) their internal structure may not be perfect L1 0 , and individual particles can become multiply-intertwined, (ii) the Pt atoms may tend to migrate towards the surface, 43,44 or (iii) an inhomogeneous alloying may be present from the beginning, as indicated by the EXAFS measurements by Antoniak. 55 The enhancement of surface-to-volume ratio (and hence the size) of a nanoparticle plays a significant role in its MCA.…”

Section: Magnetic Anisotropy Of L1 0 Fept Nanoclustersmentioning

confidence: 99%

“…We can write the effective field equation for each of the site in the cluster, and the thermal averaged magnitude at any site now can be found by using the expression, (11) where, in this case can be written as (12) One then has a set of n coupled equations involving the variables <S 1 > to <S n >. We solve this iteratively by picking a site n at random, calculating the effective field at that site and the resulting new value of <S n >.…”

Section: Thermal Effectsmentioning

confidence: 99%

“…15,16 At high temperature an fcc solid solution of Fe-Pt is observed in the A1 phase; below 1573K (and down to 973K) alloys with a nearly equal number of Fe and Pt atoms (35-55% Pt) show order-disorder transition and the L1 0 ordered phase begins to form. 11 Though the L1 0 phase is typically obtained by heat treatment of A1 phase, it can also be produced by chemical synthesis of nanoparticles. 12 Deposition of alternate Fe and Pt monolayers can reduce the onset temperature of L1 0 phase.…”

Section: Introductionmentioning

confidence: 99%

“…17 Another way to obtain L1 0 phase experimentally is by annealing alternating multi-layers of Fe and Pt. 11 Stable FePt L1 0 nanoparticles have been prepared experimentally 18 both without any covering and with Al encapsulation.…”

Section: Introductionmentioning

confidence: 99%

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Effect of structure on the magnetic anisotropy ofL10FePt nanoparticles

Kabir

Turkowski

et al. 2015

Phys. Rev. B

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ABSTRACT. We carry out a systematic theoretical investigation of Magneto Crystalline Anisotropy (MCA) of L1 0 FePt clusters with alternating Fe and Pt planes along the (001) direction. The clusters studied contain 30 -484 atoms. We calculate the structural relaxation and magnetic moment of each cluster by using ab initio spin-polarized density functional theory (DFT), and the MCA with both the self-consistent direct method and the torque method. We find the two methods give equivalent results for all the structures examined. We find that bipyramidal clusters whose central layer is Pt have higher MCA than their same-sized counterparts whose central layer is Fe. This results from the fact that the Pt atoms in such configurations are coordinated with more Fe atoms than in the latter. By thus participating in more instances of hybridization, they contribute higher orbital moments to the overall MCA of the unit. Our findings suggest that by properly tailoring the structure, one can avoid encapsulating the FePt L1 0 nanoparticles, as has been proposed earlier to protect a high and stable magnetic anisotropy. Additionally, using a simple model to capture the thermal behavior, we predict that a five-layered nanoparticle with approximately 700 atoms can be expected to be useful in magnetic recording applications at room temperature.

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Quantifying magnetism on the nanometer scale: EMCD on individual FePt nanoparticles

Schneider

Pohl

Löffler

et al. 2016

European Microscopy Congress 2016: Proceedings

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Electron energy‐loss magnetic chiral dichroism (EMCD), which is the electron wave analogue of X‐ray magnetic circular dichroism (XMCD), offers the possibility to study magnetic properties at the nanoscale in a TEM. The relatively young method of EMCD [1] was already refined to such an extent that it is possible to probe magnetic moments of thin films of a variety of ferromagnets [2, 3, 4]. By now, these measurements already surpass the resolution of XMCD experiments. However, quantitative EMCD measurements are so far only reported on thin films rather than on nanoparticles, which are expected to reveal distinct magnetic properties due to their reduced dimensions and enhanced surface to volume ratio. We report on EMCD measurements on a single FePt nanoparticle (cf. Figure 1) and compare our experimental findings with simulations. L1 0 ordered FePt is a particularly interesting material since it offers the highest magneto‐crystalline anisotropy among the oxidation‐resistant hard magnets [5]. It is therefore a promising material for future high density magnetic data storage media. The L1 0 ordered FePt nanoparticles on a STO substrate were prepared by sputtering. Prior to the spectroscopic measurements, samples in plan view geometry were subjected to mechanical thinning and grazing incidence Ar + ion milling in order to obtain 10 nm thick substrate‐free nanoparticles. The experiments were performed on a FEI Titan 3 80‐300 microscope equipped with an image C S corrector. The sample was oriented in three beam condition with the [001] easy axis of L1 0 FePt oriented (close to) parallel to the electron beam. Binned‐gain acquisition of the EEL spectra was used to optimize the S/N ratio [6]. Particular attention was paid to the analysis of the EEL spectra. A measurement route is presented that allows for the extraction of a dichroic signal from spectra that still suffer from non‐optimal S/N ratio. Our experiments are supported by simulations of EEL spectra utilizing the WIEN2k program package [7] in combination with Bloch‐wave (BW) methods. These simulations are used to (pre‐)determine optimal experimental parameters, that provide for the highest EMCD signals [8, 9]. The experiments reveal a small but reproducible dichroic signal (cf. Figure 2) that agrees well with the results of the theoretical calculations. From these experimental spectra, a ratio of angular to spin magnetic moment m l /m s = 0.08 ± 0.08 is for the first time quantitatively derived for individual FePt nanoparticles [10], which agrees well with the XMCD result m l /m s = 0.09 for a large ensemble of L1 0 ordered FePt nanoparticles [11].

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Structure and Magnetic Properties of L10-Ordered Fe–Pt Alloys and Nanoparticles

Cited by 49 publications

References 334 publications

Surface Patterning with Colloidal Monolayers

Surface Patterning with Colloidal Monolayers

Effect of structure on the magnetic anisotropy ofL10FePt nanoparticles

Quantifying magnetism on the nanometer scale: EMCD on individual FePt nanoparticles

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