Christian Menk’s research while affiliated with Hamburg University and other places

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Publications (9)


Magnetic anisotropy and spin reorientation in Co/Pt multilayers: Influence of preparation
  • Article

May 2010

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48 Reads

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26 Citations

Journal of Magnetism and Magnetic Materials

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Christian Menk

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Robert Frömter

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The magnetic properties of Co/Pt multilayers grown by ion beam and DC magnetron sputtering techniques are compared. For Pt/Co/Pt films the spin reorientation as a function of Co thickness is investigated in second-order uniaxial anisotropy approximation. The influence of the growth technique on the interface and volume contribution to the first-order anisotropy is investigated. The correlations between structure and magnetic properties are discussed.


Overcoming the field-of-view restrictions in soft x-ray holographic imaging
  • Article
  • Full-text available

February 2010

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45 Reads

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11 Citations

Journal of Physics Conference Series

C Tieg

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R Frömter

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[...]

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We present a new concept for imaging by soft x-ray holography. Microscopylike imaging capabilities were achieved by the separation of mask and sample. The use of two independent silicon nitride membranes, one for the field-of-view-defining mask and the reference beam, and the other for the sample, allows to image different areas on the sample. The movement of the field-of-view across the sample is realized by a piezomotor-driven sample stage that permits relative and stable positioning with nm-precision. We demonstrate the capabilities of the x-ray holographic microscopy (XHM) technique by showing images with 60 nm spatial resolution of an artificially structured 100 nm thick gold film with a lateral size of 19 × 4 μm2.

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FIG. 1. ͑ Color ͒ Schematic of the x-ray holographic microscopy setup. It consists of a holography mask support, a movable sample support, and a CCD detector. The membrane with the optical elements ͑ mask ͒ , i.e., the object and reference holes, is fixed in the center of the x-ray beam from the synchrotron ͑ left side of the drawing ͒ . A second membrane, which is the support for the sample, can be moved freely in a plane perpendicular to the beam. 
FIG. 2. ͑ Color ͒ Sample geometry and reconstruction of a single magnetic domain image. A cut through the scattering plane is shown in ͑ a ͒ . The sample is illuminated through the optics membrane ͓ SEM micrograph ͑ b ͔͒ . Image ͑ c ͒ is a cutout of the real part of the FFT reconstruction of the difference of two holograms acquired with opposite helicities at the cobalt L 3 absorption edge. The autocorrelation of the object hole is located at the lower right corner. The correlation of the object hole ͑ center, marked red ͒ and the two larger reference holes ͑ yellow and green, magnified in the insets ͒ with the small reference hole yield the magnetic domain patterns at the respective positions. 
FIG. 3. ͑ Color online ͒ Domain size evolution of a Co/Pt multilayer film covered by an iron wedge. Plot ͑ a ͒ gives the absorption profile ͑ normalized photodiode current ͒ at the Fe L 3 absorption edge when scanning over the Fe 
Soft X-ray holographic microscopy

January 2010

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303 Reads

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47 Citations

We present a new x-ray microscopy technique based on Fourier transform holography (FTH), where the sample is separate from the optics part of the setup. The sample can be shifted with respect to the holography optics, thus large-scale or randomly distributed objects become accessible. As this extends FTH into a true microscopy technique, we call it x-ray holographic microscopy (XHM). FTH allows nanoscale imaging without the need for nanometer-size beams. Simple Fourier transform yields an unambiguous image reconstruction. We demonstrate XHM by studying the magnetic domain evolution of a Co/Pt multilayer film as function of locally varied iron overlayer thickness.


Magnetic soft X-ray holography study of focused ion beam-patterned Co/Pt multilayer

November 2009

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34 Reads

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43 Citations

We report on Fourier transform holography (FTH) experiments on nanostructured Co/Pt multilayer films with 40 nm spatial imaging resolution. The films have been nanostructured by means of focused ion beam (FIB) milling. Applying the ion beam through the supporting membrane with controlled and homogeneous dosing allows for higher resolution magnetic structuring of the ion-sensitive film compared to direct FIB patterning. Nanostructured samples with magnetic stripes exposed to different ion doses and magnetic arrays with 200 nm lattice constant were successfully prepared and imaged by FTH. We present image-processing routines for artifact-free image reconstruction. With this, we could investigate the FIB-induced anisotropy modulation and the perpendicular domain structure in the nanostructured samples, showing how to control the domain size and configuration by applying the appropriate ion dose either homogeneously or concentrated in single spots.


Magnetic anisotropy and the cone state in Co/Pt multilayer films

May 2009

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95 Reads

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70 Citations

The magnetic anisotropy of Co/Pt multilayers is investigated. The perpendicular uniaxial anisotropy is discussed in second order approximation under a variation in Co and Pt layer thicknesses. The evolution of anisotropy constants is shown in the phase diagram of first and second order anisotropy constants. A thickness driven spin reorientation via the canted phase is observed for a single Co layer as well as for Co/Pt multilayer films. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3070644]


Imaging the Cone State of the Spin Reorientation Transition

May 2008

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40 Reads

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57 Citations

Physical Review Letters

The magnetization behavior and the domain pattern in remanence are studied in Co/Pt multilayers. The reorientation of magnetization from perpendicular to in plane is found to happen via the state of canted magnetization. In the transition from an easy axis to an easy plane a stable domain pattern in the in-plane magnetization components is found for Co/Pt multilayers. The analysis of the domain pattern reveals that the magnetization canting is such that all in-plane orientations of magnetization are equally occupied. The found structure is appointed to the cone state.


Imaging the domain pattern of the canted magnetization state in Co/Pt multilayer films

December 2007

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24 Reads

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5 Citations

Vacuum

The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern.


Magnetic antidot arrays using SiO 2 filled diblock copolymer micelles as ion etching mask

September 2007

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13 Reads

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5 Citations

Journal of Magnetism and Magnetic Materials

We present a simple method for the production of magnetic antidot arrays utilizing polystyrene-poly-2-vinylpyridine micelles filled with amorphous SiO2. By dip coating, a micellar monolayer is deposited onto Co/Pt multilayers. A hexagonal pattern with periodicity of 80nm is obtained. By Ar+ ion etching the micelle layer is transformed into an antidot array due to preferred sputtering of the SiO2 core. Further ion bombardment transfers the pattern into the magnetic film and leads to a reorientation of the perpendicular to in-plane easy axis which is attributed to intermixing of the Co/Pt multilayers.


Citations (8)


... For example, magnetization states in Co/Pt multilayer films were characterized by SEMPA (shown in Fig. 9). 85 Till now few articles concerning nanochains have been characterized by this technique. SEMPA could help to know interactions between chains. ...

Reference:

MAGNETIC NANOCHAINS: A REVIEW
Imaging the domain pattern of the canted magnetization state in Co/Pt multilayer films
  • Citing Article
  • December 2007

Vacuum

... The multilayer alloys Co x P t 1−x /P t are characterized by important properties such as a good chemical stability [1], a high coercivity [2], an important Kerr rotation [3], and a strong perpendicular anisotropy [4][5][6] which are factors of choice in the field of magnetic storage and more generally in the spintronics devices [7-10]. The fundamental advantage of using magnetic elementary excitations (magnons) as information carriers [11][12][13] is that when a magnon propagates in a sample no Joule effect takes place because no charge transport is involved. ...

Magnetic anisotropy and spin reorientation in Co/Pt multilayers: Influence of preparation
  • Citing Article
  • May 2010

Journal of Magnetism and Magnetic Materials

... This type of materials allows for a flexible tuning of structural parameters such as size, shape or periodicity of their repeating units by manipulating their molecular components [85][86][87]. Typically, the polymer layer is deposited on the magnetic film and used as a mask for ion etching until the appropriate pattern is created [88]; nevertheless, the same method can be used to define topographic templates for use with other nanofabrication methods such as the shadow deposition technique described in Section IV.A. ...

Magnetic antidot arrays using SiO 2 filled diblock copolymer micelles as ion etching mask
  • Citing Article
  • September 2007

Journal of Magnetism and Magnetic Materials

... The fourth-generation synchrotron radiation source delivers x-ray beams with high spatial coherence, which greatly promotes the research of coherent x-ray science, including Fourier-transform holography [1], x-ray photon correlation spectroscopy [2], and particularly coherent diffraction imaging. Spatial coherence information is of vital importance for the execution and data analysis of these coherence-based experiments. ...

Soft X-ray holographic microscopy

... FTH with X-rays and extreme ultraviolet waves are discussed here in one section because of their somewhat overlapping wavelengths ranges: 0.1-10 nm for soft X-rays [20,[22][23][24][25][26][27][28][29][30][31][32][33][35][36][37][40][41][42]47,[49][50][51][54][55][56][57][58][59][61][62][63]68,69,72,73,79,80,[83][84][85][86]88,89,[91][92][93]97,98,[113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128], less than 0.1 nm for hard X-rays [21,44,46,54,129,130], and 10-124 nm for extreme ultraviolet (XUV) waves [34,43,60,[64][65][66][67]70,71,82,93,131]. As a lensless imaging technique, FTH is most often performed with X-rays where a lack of high quality optical elements prevents conventional focused imaging. ...

Overcoming the field-of-view restrictions in soft x-ray holographic imaging

Journal of Physics Conference Series

... Among such cases are the precise tuning of the magnetic characteristics of thin multilayer films [8], the patterning of 2D materials [9], or the direct introduction of dopants into a solid-state host through recoil implantation [10]. Examples that rely on ion milling include patterning of magnetic multilayers [11], fabrication of optical metamaterials [12], and modification of semiconductor heterostructures [13]. Metal and dielectric layers can be used as hard masks for achieving high resolution and throughput of the FIB nanofabrication process [14]. ...

Magnetic soft X-ray holography study of focused ion beam-patterned Co/Pt multilayer
  • Citing Article
  • November 2009

... Studies have shown that when Pt(111) [16,17] or Pd(111) [18,19], is used, the total K anisotropy becomes positive (axis of easy magnetization is out-of-plane) and its intensity is greatly increased. This effect is explained by the EMP (magnetic proximity effect) existing in Pt and Pd due to the hybridization of their 5d orbitals and the 3d orbitals of Tm [20]. This hybridization can lead to an increase in the iron atom's magnetic moment, while non-magnetic Pt atoms can also acquire a non-zero magnetic moment. ...

Magnetic anisotropy and the cone state in Co/Pt multilayer films
  • Citing Article
  • May 2009

... [44,49], as temperature increases, one may expect a change of spin state from up and down magnetic domains to in-plane magnetization only at a transition temperature T r when the remanence of the hysteresis loop recorded with the field applied parallel to the film plane exceeds a value of 50% [44]. The very small values of remanent magnetization with the field applied parallel to the film plane even at T = 300 K, on the other hand, show that when the parallel magnetic field decreases from saturation to zero, the magnetization is redirected from the in-plane to a spin up and down domain state with possible canting [42,50]. Therefore, the exact temperature where the SRT takes place depends on the model one adopts. ...

Imaging the Cone State of the Spin Reorientation Transition
  • Citing Article
  • May 2008

Physical Review Letters