The GENERATION, MEASURING TECHNIQUE AND APPLICATION … · Thin coils are close to the sample positioned. Two coils in order to compensate the effect of H. Can be: Thin film coils

ƒ1

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik High Magnetic Fields

The GENERATION, MEASURING TECHNIQUE AND APPLICATION OF

PULSED FIELDS

R.Grössinger

Coworker: M. Küpferling, H.Sassik, R.Sato, E.Wagner, O.Mayerhofer, M.Taraba

ƒ2

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Content

CONTENT

Generation of static magnetic fieldsPulsed field systems

Quasistatic systemsShort pulse systems

High field magnetsMagnetisation measurements

Pick-up systemsMethods to increase the sensitivityVibrating sample techniqueSurface coils

Microtechnology for pulsed magnetic fieldsApplication of pulsed high magnetic fields

Magnetization measurementsAnisotropy

ƒ3

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Introduction

1) Introduction

High magnetic fields are important for:

Semiconductor physics (and structure, fermi surface)

Superconductivity (high Tc super- conductors)

Magnetism (magnetic phase diagrams)Material characterisationExchange couplingOnset of magnetism

ƒ4

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Static fields

Generation of static magnetic fields

Air gap of an electromagnet - fields limited by saturation magnetization – up to 2.5T

ƒ5


Hysteresograph with electromagnet from Magnet-Physik EP-2

Max. Field strength:Maximum pole diameter:Air gap:Load:Weight:

1600 kA/m (2 T, 20 kG)92 mm0-75 mm3 kW180 kg

ƒ6


Higher static fields: superconducting coil.

Fields up to 8T with Nb-TiFields up to 15T with Nb3SnFields up to 20T with hybrid.

Advantage: high fields, low power comsumptionDisadvantage: needs liquid helium, low dH/dt rate!

ƒ7


Superconducting 20T coil system from cryomagnetics (USA)

ƒ8


Superconducting coils:

ƒ9

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Hybrid magnet of NHMFL

ƒ10

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Hybrid magnet of NHMFL

ƒ11

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik NHMFL at Los Alamos

Pulsed field systems:

Quasistatic systems

1.4 GW Generator Los Alamos

ƒ12

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik NHMFL at Los Alamos

High field laboratory Los Alamos

ƒ13

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik AUSTROMAG

AUSTROMAG - T.U.Vienna:

10 MW-1s power supply.Regulated DC current over 1s. Maximum available power is limited. Primary power: 16 MVA - transformer 10 kV to 2×840V; Can be switched: series, parallel or antiparallel. ac-current - rectified - bridges 6 thyristors – I(t).Maximum dc-power: 10 MW/1 s or 5 MW/2 s or 1 MW/10sCurrent time profile – chosale - 20 free points.Delivers field plateau’s or linear dH/dt.

ƒ14


Switching of the thyristor bridges- three types of pulses:

i) Parallel switching: 2 x Imax = 13600A, Umax = 840V: highest current field pulse - one polarity.

ii) Serial switching: Imax = 6800A, 2 x Umax = 1680V: highest voltage field pulse - one polarity – 40T.

iii) Antiparallel switching: Imax = ± 6800A, Umax =± 840V. Bipolar pulse - real hysteresis measurements.

ƒ15


Electric circuit

ƒ16


10 kV2 x 1700 kVA

50 Hz

power transformer

16 MVA

thyristor rectifier12-pulses

2 antiparallelbridges

passive smoothing

LCcircuit

regulating electronicinput H(t)

! SECURITY !

measuring electronics

temp. controller

2 x 570V/6800Aparallel or seriel

2 x 600V, 8300A/1s

0 Hmax =

20 Tm0Hmax =

35 Tm 0 Hmax =

40 Tm

high-temperaturesystem

300K < T < 800K

low-temperaturesystem

1.5K < T < 300K

test systemmodulation

magnetostriction

Block diagram of the “Austromag”high field installation.Low temperaturesystem: max. 40 T in 25 mm bore; temperature between1.5 K and 300K

High Temperature system: maximum 35T in 40 mm;

300 K < T < 800K

ƒ17

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Short pulse systems

Short pulse systems

Typical pulse duration 1 - 50 ms.Energy source: condensator battery - kJ. Available power can be varied by the time constant of the system.

Consist of:

Energy source - C.U2/2charging unit - reproducibilityPulse magnet - diameter, homogeneitymeasuring device – pick-up coils + electronicData storage + PC

ƒ18

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Short pulse system

C=8mF/24mFU=2500V

PC

PULSED FIELD SYSTEM

CHARGING

CONDENSATORBATTERY

HIGH FIELD

TRANSIENTRECORDER

UNIT

MAGNET

Pick- UpSystem

PREAMPLIFIER

GAIN: 1-10

2/4 LAYERS

Block diagram of the condensatordriven pulse field facility

ƒ19

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Magnets

High field magnetsOptimized with respect to the available power, the heating of the magnet and the stresses.

Heating of the magnet:

j(t)...current density

D....density of the conductor,

c(T)....specific heat

ρ(T)...specific resistivity of the conductor.

j t dt D c TT

dTT

T2

1

2( ) . ( )

( )= ∫∫ ρ

ƒ20

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Magnet

Stresses in the magnetStress in a high field magnet scales with B2

ƒ21

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Leuven Magnet

ƒ22


AUSTROMAG 40T magnetField versus time profile of a magnet driven by a maximum power

of 5.5 Mw (I = 10kA); the temperature rises up to 150 K.

ƒ23


STRESS in the AUSTROMAG magnet

Axial, radial an tangential stresses at 38 T in the middle plane of the magnet.

ƒ24

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Magnetization measurements

Magnetisation measurementsPick-up systems

N Nr

N

N

rN/2 N/2

Nr

1

2

1r2

a)

b)

c)

Dipol: R12N1 = R2

2N2

Axial system: simple –vibrational sensitive

N/2-N-N/2 system: long

[ ]

[ ]

u t N K R dHdt

dMdt

u t N K R dHdt

1 0 1 1 12

2 0 2 2 22

( )

( )

= − +

= −

µ π

µ π

ƒ25

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Pick-up

Compensatable pick-up system used in pulsed fields up to 50T – IFW Dresden.a

b

c

56

2k73k3

4k2

ƒ26

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Pick-up

Problems:

Temperature dependent measurements - compensation depends sensitively on the position of the pick-up system. with respect to the high field magnet. With increasing field the noise increases due to vibrations. Metallic systems - the eddy currents also cause a measuring error.

maximum achievable sensitivity aout 0.01 emu.

Sensitivity depends directly coupling between sample and pick-up coil. Small samples - thin films - very difficult!

ƒ27

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Eddy currents

How eddy currents are created

ƒ28


Eddy Currents due to pulsed magnetic fieldsCu-sample – cylinder – with increasing diameter.

-6 -4 -2 0 2 4-800000

-700000

-600000

-500000

-400000

-300000

-200000

-100000

0

100000

200000

300000

400000

500000

600000

Cu, cylinder, h=8mm d=2mm d=6mm d=8mm d=9,8mm d=4mm

8mF, T=9.1ms

M (A

/m)

µ0H (T)

ƒ29


Cu-sample – cylinder – with increasing length.

-6 -4 -2 0 2 4

-100000

-50000

0

50000

100000

150000

Cu, cylinder, d=4mm h=2mm h=4mm h=6mm h=10mm h=8mm

8mF, T=9.1ms

M (A

/m)

µ0H (T)

ƒ30


EDDY CURRENTS ON MAGNETIC SAMPLES

-6 -4 -2 0 2 4-600000

-400000

-200000

0

200000

400000

600000

Ni, cylindre, d=4mm, h=8mm

ρ=8908kg/m3

m=0,89183gannealed, 4h, 500°C8mF, 2000V

M (A

/m)

B (T)

-6 -4 -2 0 2 4-600000

-400000

-200000

0

200000

400000

600000

Ni, cylinder, 8mFeddy-current-corrected withspecific resistance of 8µΩcm

M (A

/m)

B (T)

Ni

ƒ31

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Measurement methods

Methods to increase the sensitivity

Only so-called “DC-methods” used. Integrating “everything” which comes. High noise - limits achievable sensitivity.

Methods which enhance signal to noise ratio -lock-in technique + improve coupling between the sensor ( the pick-up coil) and sample.

ƒ32

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Measurement method

Vibrating sample technique

Static magnetometers - vibrating sample method.Lock-in technique - improves signal to noise

ratio. Pick up coils - ac-signal - proportional to M.

Pulsed field systems:i) Modulation method – eddy current problems. ii) Piezo electrique actuator Effects of induction voltages can be suppressed.

ƒ33

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Measurement method

Surface coils

Thin coils are close to the sample positioned. Two coils in order to compensate the effect of H. Can be: Thin film coils - bad L/R ratio – phase problemsWire wound coils

The ultra-thin pick-up coils are manufactured in thin-film technique as indicated in the figure.

ƒ34

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Surface coils

Thin film coils

Magnetization curve taken onBaFeO-film.

ƒ35

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Surface coils

Wire wound coils (Magnet Physik)Low impedance!

Type PKS 5 PKS 3

Turn area, approx. 5 cm2 3 cm2

Coil thickness 1 mm 0,5 mm

Coil width 5 mm Ø 5 mm Ø

ƒ36

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Toulouse - Cantilever

Microtechnology for pulsed magnetic fields

ƒ37

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Cantilever

TU-Vienna: U – shaped cantilever

Deflection of the cantilever is detected optically

ƒ38

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Cantilever

Characteristic of the combination cantilever-optical readout. The inset shows how the displacement of the cantilever is measured. The diagram is scaled to unity.

ƒ39

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Results

Application of pulsed high magnetic fields

0 6 12 18 24 300

20

40

60

80

100

120

YCo5-xCux perpendicular

280 K, x = 2 280 K, x = 1 280 K, x = 0 4.2 K, x = 0 4.2 K, x = 1 4.2 K, x = 2

M(A

m2 /k

g)

µ0Hint

ƒ40


Accurate hysteresis measurements on industrial magnets

-1500 -1000 -500 0 500 1000 1500

-0,4

-0,2

0,0

0,2

0,4

µ 0M [T

]

µ0H [kA/m]

PTB - Ferrite cylinder long pulse short pulse

dynamic: JHC = 213 kA/m; Br = 0.358 TPTB: JHC = 208 kA/m; Br = 0.362 T

ƒ41


Room temperature hysteresis loop of a two phase spherical and a cylindrical Nd-Fe-B sample. The curves were corrected for the

demagnetizing factor.

-6 -4 -2 0 2 4 6

-1,0

-0,5

0,0

0,5

1,0

cylindre sphere

corrected with demagnetizing factor

µ 0M

(T)

Hin (MA/m)

ƒ42


Anisotropy of nanocrystalline mechanical alloyed Pr-Fe-

180 200 220 240 260 280 3007

8

9

10

11

12

Pr18Fe76B6

Pr12Fe82B6

Pr9Fe85B6

µ 0H

a (T)

Temperature (K)

ƒ43


Magnetic viscosity

0.4 0.8 1.2 1.6

0

5

10

15

20 SmCo5-x

Cux

Cu1.5

annealed Cu

2.0 annealed

Cu2.5

annealed Cu

3.0 annealed

Cu2.0

as-cast Cu

2.5 as-cast

dH/d

t [(G

A/m

)/s)]

Hc [MA/m]

Coercive field as a function of the sweep rate dH/dt measured in as cast and annealed SmCo5-xCux

ƒ44


Magnetostriction

-5 -4 -3 -2 -1 0 1 2 3 4 5

-40

-20

0

20

40

60

80

100Bariumferrite HF 24/16 T=300K λpc

λcc

λpp

λcp

Mag

neto

strik

tion

[ppm

]

B [T]

Magnetostriction measurements at room temperature on an anisotropic barium ferrite magnet made by Schramberg (HF24/16).

ƒ45

LAW3M April 2003R.Grössinger Inst. f. Festköperphysik Summary

Summary of high magnetic fields

High magetic fields are necessary for many aspects of solid state physics

Pulsed fields allow also smaller laboratories access to medium up to high fields.

Measuring technique still has to be improved.

Many applications in the area of magnetism. Magnetization, anisotropy, magnetostriction.....

Documents

The GENERATION, MEASURING TECHNIQUE AND APPLICATION … · Thin coils are close to the sample positioned. Two coils in order to compensate the effect of H. Can be: Thin film coils