Argonne National Laboratory is a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC.

1.  D. Haskel, et al. Eur. Phys. J. Special Topics 208, 141-155 (2012).

2.  S.H. Liou, et al., J. Appl. Phys. 85, 4334 (1999). 3.  J. M. Logan, R. Harder, L. Li, D. Haskel, P. Chen, R.

Winarski, P. Fuesz, D. Schlagel, D. Vine, C. Benson, and I. McNulty. J. Synchrotron Radiat., (accepted).

4.  M. Holt, et al., Annu. Rev. Mater. Res. 43, 3.1-3.29 (2013).

5.  Y. Choi, et al., arXiv:1405.4319 [cond-mat.mes-hall]. 6.  I. K. Robinson and R. Harder, Nature Materials 8, 291

(2009). 7.  G. Xiong, et al., Adv. Mater. 26, 7747-7763 (2014).

§  At beamline 26-ID-C we will perform a scanning nanodiffraction experiment on Gd nanocrystals with magnetic dichroism contrast to get a map of magnetization and strain.

§  We are incorporating a variable magnetic field

apparatus into our experiment at beamline 34-ID-C to have dynamic control over the magnetization in CoPt nanocrystals while collecting coherent diffraction patterns.

Bragg Coherent Diffractive Imaging (BCDI) §  BCDI enables the investigation of 3D

morphology, electron density, and strain inside compact, crystalline objects at length scales to the 10 nm scale. 3D images of morphology and internal strain are reconstructed from coherent diffraction patterns using iterative algorithms [6].

§  For dichroic-BCDI, we collect coherent diffraction patterns with left- (LCP) and right- (RCP) circularly polarized x-rays. The difference between LCP and RCP reconstructed objects isolates the magnetic component of a nanocrystal [3]. Work being done at APS beamline 34-ID-C

Scanning nanodiffraction: §  A nanofocused (25nm FWHM) x-ray

beam is rastered across sample while aligned to a structural Bragg peak. Local strain can be determined from diffracted intensity profile on CCD [4].

§  Use of nanofocused, circularly polarized x-rays provides magnetization information in addition to the strain information.

§  We have demonstrated the ability to focus circularly-polarized x-rays to a sub-50 nm spot size using a diamond XPR we installed at APS beamline 26-ID-C.

§  Diamond x-ray phase retarders (XPRs) enable the generation of circularly polarized x-rays in the hard x-ray (>3 keV) regime.

§  They achieve a high degree of circular polarization, are tunable over a wide energy range, and allow fast polarization switching.

X-RAY IMAGING OF STRAIN AND MAGNETIZATION AT THE NANOSCALE How defects and internal strains affect magnetic domain formation Jonathan M. Logan1, Ross Harder2, Luxi Li2, Daniel Haskel2, Daniel Rosenmann1 , Martin V. Holt1, Robert Winarski1, Peter Fuesz1, Tenzin Sangpo3, Ian McNulty1, 1 Center for Nanoscale Materials, Nanoscience and Technology Division, Argonne National Laboratory 2 Advanced Photon Source, Argonne National Laboratory 3 Reed College

§  Synchrotron-based hard x-ray sources have enabled revolutionary breakthroughs for probing magnetism and strain at the nanoscale.

§  Many of these advanced methods to study magnetism and strain are performed in the Bragg-diffraction geometry, offering the possibility of combining them into a single probe carrying dual information.

§  For a ferromagnet, charge and magnetic diffraction peaks overlap in reciprocal space. A differential measurement of scattered intensities for left and right circularly polarized x-rays removes the strong charge scattering and yields charge-magnetic interference scattering containing information on magnetic domain orientation [1].

§  We have installed diamond x-ray phase retarders (XPRs) at Sector 26-ID-C and Sector 34-ID-C of the Advanced Photon Source to produce circularly polarized x-rays and are actively developing techniques to simultaneously image strain and magnetization at the nanoscale.

CONCLUSIONS NEXT STEPS REFERENCES

2-D IMAGING 3-D IMAGING

ABSTRACT MOTIVATION METHODS §  Lattice strain and magnetization are

coupled by the magnetoelastic energy. Therefore, the magnetic domain configuration often depends on local strain fields.

§  We wish to explore this connection between strain and magnetization simultaneously with ~25 nm resolution.

Single- (S) and multi- (M) magnetic domain CoPt nanocrystals. MFM image from [2] Illustration of the diamond XPR setup installed at Sector 34-ID-B [3]

§  We have an upcoming measurement (Aug 16-20) to measure magnetic domains and strain in gadolinium (Gd) crystals using nano-diffraction with magnetic dichroism contrast.

Geometry for scanning nanodiffraction [5]

Geometry for BCDI [7]

Coherent Diffraction Patterns of a CoPt nanocrystal

§  Efforts are underway to reliably isolate magnetic dichroism contrast from reconstructions of these CoPt BCDI datasets.

SEM image of a CoPt crystal

§  We installed diamond XPRs at APS beamlines 26-ID-C and 34-ID-C for the generation of circularly polarized synchrotron x-rays.

§  We are currently combining the existing capabilities (e.g. scanning nanodiffraction; BCDI) with circularly polarized x-rays to gain magnetic contrast.

§  Magnetic nanocrystals such as epitaxial Gd nanocrystals and faceted CoPt nanocrystals have been developed for these studies.

Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.