Metallic magnetic Metallic magnetic calorimeters (MMC) for high calorimeters (MMC) for high resolution x-ray spectroscopyresolution x-ray spectroscopy

Loredana GASTALDO, Markus LINCK, Sönke SCHÄFER, Hannes ROTZINGER, Andreas BURCK, Sebastian KEMPF , Jan-Patrick PORST,

Andreas FLEISCHMANN, Christian ENSS, George M. SEIDEL

Inverse Temperature T1 [K 1]

Ma

gn

etiz

atio

n

M

[A/m

]

Au:Er 300 ppm

Temperature T [mK]

S

pe

cific

he

at

C

[1

04 J

mo

l1K

1]

Au:Er 300 ppm

Detector setupDetector setup

Thermodynamic properties of interacting spins (RKKY) can be calculated with confidence by mean field approximations or Monte Carlo simulations optimization by numerical methods is possible

totC

ET

totC

E

T

MT

T

M

11

IM2GR

+ + + +I V

50 mK 4.2 K 300 K

B

Very stable material suitable for long lasting measurements

Fluctuations of energy in a canonical ensemble

Magnetic Johnson noise(thermal currents in the metallic sensor )

Flux noise of the SQUID-magnetometer energy sensitivity close to quantum limit required,

1/f noise

sensorelectron

SQUID

(order of magnitude: 1eV for a 10 keV x-ray detector)

Cabs Cspins

100 .. 502/ LS

Noise & energy resolutionNoise & energy resolution

4/1

1

02 2436.2

TCkE absBFWHM

Aluminum thin window

Lead

Collimator

Brass holder Circuit board

Field coil

Superconducting shield (lead)

Detector set-upDetector set-up

Detector SQUID: KSUP-10-50 (IBM)

Amplifier SQUID: CCBlue (IPHT Jena)

Sensor Au:Er 600 ppm x (12.5)2 x 8 m3 Absorber Au 180 x 180 x 5 m3 stopping power above 98% @ 6 keV

Pulses acquired at different temperatures and at different magnetic fields

Detector SQUID

Magnetization and chip temperatureMagnetization and chip temperature

M

agne

tic F

lux

Tbath [K]T

chip

[K]

Dissipation on the SQUID chip leads to a decoupling of the chip temperature from the bath temperature

Pulse analysisPulse analysis

Rise time 100 s fast decay time 650 s Decay time slow decay time 8.1 ms

Time t [ms]

The amplitude of pulses saturates at low temperatures and high fields

Temperature T [mK]

5555Fe energy spectrum Fe energy spectrum

C

ount

s / 2

eV

C

ount

s / 1

5 eV

Energy E [keV] Energy E [keV]

Very low background A 3.695 keVB 3.775 keV

Energy [keV] Transition

Energy resolution and linearityEnergy resolution and linearity C

ou

nts

/ 0

.24

eV

C

ou

nts

/ 0

.12

eV

Energy Energy E [keV]

Energy E [keV]

Rela

tive

pu

lse a

mp

litu

de A

Measu

red

en

erg

y E

exp [

keV

]D

iffere

nce

[eV

]

Energy E [keV]

A -

Ai

TFN 0.38 eV+ SQUID 1.14 eV+ 1/f 1.6 eV ???? 1.85 eV still missing!

1/f2 due to temperature fluctuations of the chip

Conclusion and future plansConclusion and future plans

•2,7 eV energy resolution is a good result but it does not rapresent the limit of magnetic calorimeters

•Improvements of our detector will follow the good results we are obtaining with microstructuring techniques

-166Er enriched Au:Er sputter target-Sputtered Au:Er sensor-Overhanging absorber