LTD12, Paris

Microstructured magnetic calorimeter

with meander shaped pickup coil

A. Burck

S. Kempf, S. Schäfer,

H. Rotzinger, M. Rodrigues,

T. Wolf, A. Fleischmann,

L. Gastaldo, C. Enss

Kirchhoff-Institute for physicsUniversity Heidelberg

LTD12, Paris

weak thermal link

Metallic magnetic calorimeter

sensor: Au:Er (~100-1000 ppm)

x-ray

dc-SQUID magnetometer

Wärmebad

paramagnetic sensor

absorber

B

thermal bath

LTD12, Paris

cylindrical sensor

circular SQUID-loop

external magnetic field

planar sensor

meander shaped pickup loop

with transformer coupling

Sensor readout schemes

LTD12, Paris

Why meander shaped pickup coils ?

• natural 2d geometry with high filling factor

• no external field coil needed

• bias field is multipole field of high order:

• magnetic detektor response has multipole character

• reduced magn. cross talk between pixel

• reduced pickup of magnetic Johnson noise

• field decays exponentially with distance allows for superconducting absorbers

LTD12, Paris

Characterisation: Prototype-detector

setup:

• large area detector, Asensor= 1mm•1mm

• sputter deposited sensor, Au:Er 750 ppm,

natural isotope mixture ( 22.9 % 167Er)

• Csens 0.4 nJ/K

• expected ΔEFWHM ~ 25eV

• no absorber

3.5 mm

LTD12, Paris

Magnetization

magnetization of the sputter deposited Au:Er shows bulk-properties for temperatures in the range between 2 K-300 K promising result

LTD12, Paris

Magnetization

theory

Au:Er-sensor can reliably be microstructured

magnetization of the sputter deposited Au:Er shows bulk-properties for temperatures down to 45 mK

deviation below 45 mK is most likely caused by a general thermal decoupling of the detector from the heat bath

bath

Au:Er, 750 ppm

LTD12, Paris

Fluorescence spectrum of 55Mn

Baseline

• 17700 events (50 minutes)

• rate: ~ 15 events/s

• T = 30 mK, IF = 55 mA

Averaged Kα-pulse

IF = 40

mA

T = 39

mK

time

Kα-line

EFWHM=162 eV EFWHM=106 eV

LTD12, Paris

Signal size and Heat capacity

measured signalsize is 30% - 50% smaller than the expected behaviour

measured heat capacity is a factor of 1.3 – 2 larger than the expected behaviour

additional heat capacity and/or loss of phonons

LTD12, Paris

Summary & Outlook

meander: promising geometry

reduced cross talk

reduced magn. Johnson noise

no external field coil needed

better SNR

results: magnetisation of the sputter deposited Au:Er shows bulk properties down to 45

mK

sensor can reliably be microstructured

microstructured detektor shows promising results

future: continue with microstructering ...

arrays + multiplexing

theory

Au:Er, 750 ppm