# Presentation: 143331

## Karine CHESNEL

**ALS**

- New developments
- and investigations
-  with coherent magnetic
- scattering at ALS

***WORKSHOP***
***Magnetic Nanostructures,***
*** ******Interfaces, and New Materials: ***
***Theory, Experiment, and Applications***

## Collaborations

- Steve Kevan		*University of Oregon*
- Joshua Turner
- Jeffrey Kortright 	*Lawrence Berkeley Lab*
- Eric Fullerton		*Hitachi, San Jose*
- Olav Hellwig 		(BESSY, Germany)
- Larry Sorensen 	*University** of Washington*
- Michael Pierce
- Shouheng SUN	*IBM, New York*
- Kannan KRISHNAN	 *University of Washington*

- K.Chesnel

## Outline

- Introduction
- The coherent scattering endstation at ALS
- First investigations on nanoparticles
- Different way to use magnetic Speckle

- K.Chesnel

## How obtaining magnetic speckles?

**Light**
**(Soft X)**

**Temporal**
**Coherence**

- K.Chesnel

## Coherent Soft X-Ray Beamline (BL12.0.2)

- Rosfjord et al. (2004)

- Energy range 200-1000eV
- Coherent flux at 500eV:
- ~ 5 1010 ph/sec/0.1%BW

- K.Chesnel

## Coherent Soft X-ray Magnetic Scattering endstation

**Coherent Soft X-ray Magnetic Scattering endstation**

***Flangosaurus***

- K.Chesnel

## Flangosaurus

***Flangosaurus***

- K.Chesnel

## Flangosaurus

***Flangosaurus***

- Octopolar magnet

- Unit pole

**H**

**x**

**y**

**z**

- Produce Magnetic field in any direction
- Maximal amplitude 0.6 T

- Water
- Cooling
- system

- Current
- Input
- (100A)

- K.Chesnel

## Flangosaurus

***Flangosaurus***

**Scattering**
**chamber**

**Light**

**Optical**
**table**

**Cryogenic**
**Sample-**
**holder**

**Magnetic**
** ****manipulator**

**Load-lock**
**chamber**

**Bellow**

**Sample**
**location**

**Rotation**
**brackets**

***Pressure***
***10******-8****** mBar***

- K.Chesnel

## Flangosaurus:

***Flangosaurus:***
***Cryogenic Sample holder + pinhole mechanism***

- K.Chesnel

## Experimental possibilities

** ****High oversampling condition**
** ****In-situ 3D magnetic field**
** ****Sample cooling (cryostat)**
** ****Investigation of the full main scattering plane**
** ****2D detection with high resolution**
** ****Fast detection**

- K.Chesnel

## Different geometries specificities

- K.Chesnel

## Probing the magnetism in nanoparticles

- K.Chesnel

## Co particles 8-9nm (variable packing)
Fe3O4 particles variable size 4-16nm 

- Probing the magnetism in nanoparticles

- Different systems under study:

- Co particles 8-9nm (variable packing)
- Fe3O4 particles variable size 4-16nm

*Sources S. Sun, K Krishnan...*

- Kortright et al. (2004)

- K.Chesnel

## Characterization  with polarized light (BL4)

**Co nanocrystals**

- K.Chesnel

## Coherent 2D scattering on nanoparticles

- Co Nanoparticles assembly
- precipitated on TEM grid

- Energy optimized at
- Co L3 edge: =1.58 nm

- K.Chesnel

## General 2D scattering 

- TEM image (K.Krishnan)

- VERY
- HERTEROGENEOUS!!

**Localized**
** ****peaks => **
**Ordered**
**area**

**Isotropic**
**Pattern**

**Another Ordered area**

- General 2D scattering
- Patterns (no pinhole)

- ALL patterns distributed
-  along a RING
-  ordered area d~ 12nm
-  disordered d~ 13nm

- K.Chesnel

## Effect of magnetic field  in linear polarization

- Scattering peak (charge +magnetic)

- Full
- scattering

- Difference
- Remanence
- Saturation

- With PERPENDICULAR field:
-  I (saturation) > I (remanence)

- (Effect ~0.5%)

- With IN PLANE field:
-  I (saturation) < I (remanence)

- At saturation all particle moment are pointing
-  the same direction and contribute to the peak

- With linear polarisation
- X rays are not sensitive to the in plane component

- - Ordered area

- K.Chesnel

## Effect of magnetic field 

- – isotropic area

- With PERPENDICULAR field:
-  I (saturation) > I (remanence)

- Effect ~4%

- Difference
- Remanence - Saturation

- Full scattering

- Scattering signal
- (charge +magnetic)

- It seems isotropic areas show a stronger
- tendency to AF order at remanence,
-  while ordered area are more F...

- K.Chesnel

## Obtaining a Speckle pattern: degree of coherence/ pinhole size (Co edge)

- No pinhole 10sec

- 5 m pinhole 100s

- 3 m pinhole 300s

- C=1%

- C=12%

- ...Dainty law

- Transverse
- coherence
-  length
- c~1m

- K.Chesnel

## Static spatial cross correlation (metrology)
Slow dynamic on spatial correlation
Fast dynamic time correlation

- Slow dynamic on spatial correlation
- Fast dynamic time correlation

- What the Speckle pattern tell us?

- Speckle pattern

*Three Ways to use the speckle*

- K.Chesnel

## 1. Static Speckle metrology 

**1. Static Speckle metrology**

- Cross-correlation
- between two
- speckles patterns
- A and B

- A

- B

*Correlation coefficient*

**Magnetic **
**Memory**

-  Pierce et al. PRL **90**, 175502 (2003)

******= 0 no memory**
******= 1 total memory**
**(exact same pattern) **

- K.Chesnel

## Major Loop Return and Conjugate Point Memory

- major loop

**VERY HIGH MEMORY !**

- K.Chesnel

## 2. Slow dynamic 

- Diffuse ring
- (disordered area)
- Each frame: 10 sec

- K.Chesnel

## 3. Fast dynamic 

- Scattering
- Signal
- I (t)

- Principle

**3. Fast dynamic**

- K.Chesnel

## Map the dynamic (H,T)

- First results on Fe3O4 nanoparticles

- Fe L3 edge
- 25 m pinhole/sample
- 300 m hole/detector
- Intensity 15 000 cps/sec

-  Evolution with T
- (through  blocking transition)
-  Effect of magnetic field

- K.Chesnel

## Conclusion

- New endstation  for coherent magnetic scattering       now functional at ALS BL12
- First investigations on Co and Fe3O4 nanoparticles   with coupled measurements in **incoherent** light (XMCD, SAXS) and **coherent** light (speckle)
- Static speckle study: magnetic memory
- Slow dynamic: time scale > 1sec
- Fast dynamic: time scale 10 sec – 1sec

- K.Chesnel

## “Speckle” techniques 

** ****Speckle Metrology (spatial)**
** ****Slow and fast dynamic**
** ****Lensless magnetic imaging**

- General future directions

_*Candidates*_* *
- Metallic thin films
- Co/Pt, FePd, FePt...
-  Patterned media
-  Nanoparticles
-  Exchange bias
-  Manganites CMR
-  Cuprates
-   superconductivity

- K.Chesnel