LTD12, Paris Microstructured magnetic calorimeter with meander shaped pickup coil A. Burck S. Kempf, S. Schäfer, H. Rotzinger, M. Rodrigues, T. Wolf, A.

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

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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

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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