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NEWS

December 2023 ESRFnews

Researchers in Germany have found

that a first-order magnetic transition

in alloys takes place in two steps.

The work opens a new pathway to

disentangle the interplay between

structural, magnetic, and electronic

degrees of freedom in such transitions.

Alloys with a first-order magnetic

transition play an important role

in the manufacturing of advanced

refrigeration systems, sensors and

other devices. The transition is unique

because it happens suddenly, and is

connected to how the magnetic part, the

electronic part, and the structural part of

a material all work together. In principle,

it can cross several metastable states

– at one point taking place within

the magnetic subsystem, while at

another taking place in the structural or

electronic subsystems.

With the aim to disentangle the

nature of the first-order magnetic

transition, researchers led by the

University of Darmstadt designed two

new experimental set-ups, allowing

the simultaneous measurement

of magnetisation, longitudinal and

transversal magnetostriction, and

temperature change of the sample.

They then carried out simultaneous

measurements of a lanthanum–iron–

silicon (LaFe

11.8

Si

1.2

) alloy in the lab,

before coming to the ESRF to perform

X-ray absorption spectroscopy

(XANES) and X-ray magnetic circular

dichroism (XMCD) experiments at the

ID12 beamline (below).

The researchers found that the

magnetic change does not happen at

once, but instead takes place in two

separate steps: the first defined purely

by magnetic contribution; the second

with participation by both the magnetic

and structural subsystems (Appl. Phys.

Rev. 10 031408).

Magnetic alloys take two

steps to transition

A team based in France has used ESRF

techniques to uncover an unusual and

unstable component in Leonardo Da

Vinci’s Mona Lisa. They believe the

addition was part of an effort by the

Italian Renaissance painter to create

a thick paint that would cover the

wooden panel behind his most famous

masterpiece.

Leonardo Da Vinci experimented

with innovative techniques in his oil

paintings. In each of his artistic works,

the materials used and the build-up of

layers are different. But while he wrote

numerous manuscripts about his other

interests in areas such as engineering

or architecture, he left very few clues

about his painting materials.

Now researchers from various

French institutions including

the CNRS Supramolecular and

Macromolecular Photophysics

and Photochemistry Laboratory

at the École normale supérieure

ParisSaclay the National Centre

for Research and Restoration in

French Museums C2RMF and

the Musée du Louvre have brought

a microsample of the preparation

layer of the Mona Lisa to the ESRF

ID22 ID13 and ID21 beamlines for

analysis by synchrotron radiation

highangular resolution Xray powder

diffraction, micro X-ray diffraction

and micro Fourier-transform infrared

spectroscopy. For comparison, they

also brought several fragments from

another of Leonardo’s masterpieces,

The Last Supper.

The team discovered a relatively

high amount of plumbonacrite,

an usual compound that they had

previously identified in a study of The

Night Watch by the Dutch Golden

Age painter Rembrandt van Rijn,

painted two centuries later. At first,

Leonardo’s manuscripts proved to

be of little use, especially given the

different terminologies he used, but

eventually the researchers found a

reference to the compound in the

context of a pharmaceutical practice.

They believe it was formed by a

specific mix of oil with lead oxide and

that Leonardo intentionally used it in

his paintings to create a thick opaque

ground layer J Am Chem Soc DOI

101021jacs3c07000

We faced the additional challenge

that there are very few scientific

analyses of the Mona Lisa and of

Leonardos paintings in general so

it was difficult for us to compare our

results with previous studies says

Marine Cotte scientist in charge of

the ID21 beamline

Behind the

enigmatic smile,

the chemical

compound

plumbonacrite,

possibly to help

cover up the

wooden paint

board.

I. F A Z L I C, M. C O T T E & V. G O N Z A L E Z

Mona Lisa hides unusual compound

E S R F/P.J A Y E T