A New Measuring Technique for the Characterization of Magnetic Materials in Pulsed Magnetic Fields

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1 A New Measuring Technique for the Characterization of Magnetic Materials in Pulsed Magnetic Fields Authors: J. H. Espina Hernández Supervisors: Prof. Dr. R. Grössinger Prof. Dr. E. Estévez Rams

2 Antecedents Thin superconducting films were measured using an open-flat pick-up coil in very strong magnetic fields. [Lagutin et al, Rev. Sci. Instr. 66 (8) 1995; Weckhuysen et al, Rev. Sci. Instr. 70 (6) 1999] It had been demonstrated the use of a pulsed field magnetometer for the quality control in the production of permanent magnets. [Grössinger et al, IEEE Trans. Magn. 38 (5) 2002]

3 Hypothesis The local area measurements contribute to the experimental study of several physical phenomena. General Objetive To develop a new measuring technique in pulsed magnetic fields.

4 Objects of Study A thin-film pick-up coil (TFC) designed at the TU-Vienna [G. Handreich,.., J.H. Espina-Hernández, Sensors and Actuators A, 91:57-60, 2001] Features A eff = 4 cm 2 R 125 kω 1 mm L 25 µh [Mohan et al, IEEE of Solid-State Circuits 34 (10), 1999] C 55 pf [measured with the Kiethley 3322 LCZ meter]

5 Wire wound pick-up coil (WWC) produced by MAGNET-PHYSIK Dr. Steingroever GmbH, Germany [ Dr. Steingroever and Dr. Ross, Magnetic Measuring Techniques, 1997]. Features A eff 5 cm 2 R Ω 1 mm L 42 µh [measured with the Kiethley 3322 LCZ meter]

6 Specific objetives To analyze the electrical behavior of the TFC and the WWC. To demonstrate the possibility to calibrate the magnetization for the local area measurements. To demonstrate the advantages and disadvantages of the measurements using this type of pick-up coil - sample arrangement in comparison to the standard pick-up coils. To establish that the local eddy current measurements contribute to the improvement of the correction of this unlike effect, with the aim to incentive the application of the pulsed field magnetometer as standard quality control machine at the magnet production industry.

7 Pulsed Field Magnetometer (PFM)

8 Electrical circuit of a PFM i f = U ω max L F e β t sen ( ω t) dh dt = U ω A max efff e β t [ ω cos( ω t) β sen( ω t) ]

9 Compensation of a pick-up coils system V = A L dh dt + K inds µ 0 effp M 1 dm dt V = µ indc 0 A effp L M dh dt V out = V inds V indc dm dt Zerosignal is always present, it should be saved in the PC

10 Method to obtain the hysteresis loop A first shot with the sample, (Vind=VM+VZ) A second shot without sample, (VZ) Hysteresis loop t T t 0 ( ) V ind V z

11 Plastic rod DB-15 connector BNC connectors Field Coil Volumetric Pickup LPC Working station

12 Holders for the TFC and WWC

13 Plastic rod Sketch of the local area magnetization measurements

14 Electrical study of the TFC and the WWC

15 Zerosignal obtained by simulation for the TFC C = 0.1 nf ϕ

16 Zerosignal obtained by simulation for the WWC C = 0.1 nf ϕ cte

17 M/M o (a.u) WWC TFC Hysteresis loop for a Ba-M sample obtained with the WWC and the TFC µ 0 H ext (T) The high impedance of the TFC pick-up does not affect the shape of the loop.

18 Calibration using the WWC and the TFC

19 Calibration of H Volumetric pick-up coils systems measuring well known phase transitions; i.e: the spin-flop of the MnF2 (µ0hcr = 9.2 T a 4.2 K) measuring HA of Ba-M, the singularity shows up at 1320 ka/m, and it changes 1 % from K For low Temp. For high Temp.

20 Systems with the TFC and the WWC pick-up Aeff is known!!! v indp = A effp K0 e ω β t [ ω cos( ω t) β sen( ω t) ] Data: DHDTCILIN8MF_DHDT Model: PulseField Chi^2 = R^2 = k ± w ± B ± Ae ±0 Accuracy around 1 % V ind (V) Induced Signal 2,5 T Fit A effect =5.459 x 10-4 m 2 µ 0 H max =2.379 T µ 0 H 0 =2.84 T Holder SCD, 8 mf, 1.1 kv Room Temp t (s) CalSCDHolderCilindro.OPJ

21 Calibration of M Volumetric systems It is defined a calibration sample (Ni, Fe, Fe3O4, BaFe12O19) with well known parameters (m, MS). Sample under investigation M y = Vind _ Vi CM [ A / m] Voli In case that 1 Vol = Vol C i C M = M S _ C Vol Vind _ V C C 2 [ Am / V s] M y = M S _ C Vind Vind _ V i _ V c

22 10 cylinders, d=10 mm y 1 mm < h < 10 mm Local pick-up coils 12 Complex behavior of the induced signal respects to the volume of the sample Maximum of the V int ~ M (V.s) Height of the sample (mm)

23 Local Measurements, Applications

24 Local demagnetizing factor measurements SPD technique n M n H HA measurement Asti and Rinaldi, J. Appl. Phys., 45 (8), Aug BaFe12O 19 n = 2 H Aint = 1.65T, J S = 0. 41T N ml = H Aext J S H Aint

25 Sample B1 B2 Teo. In. Mid. Out x x x x B x x BL BL The theoretical values of Nm are valid only at the center of the sample The study of the homogeneity of the stray field, the demagnetizing field and the magnetization

26 Measurement of the transverse susceptibility H H st n χt n H Asti and Rinaldi, J. Appl. Phys., 45 (8), Aug Singularity occurs at HA Paretti and Turilli, J. Appl. Phys., 61 (11), Jun v ind t = k h ω sen ω χt 0 ( t) Amplificador Look-in

27 Eddy current measurements

28 Previous work by M. Kuepferling et al m ( σ ) = k,.. dh dt k k Cu Al = ρ ρ Al Cu m m Cu Al = ρ ρ Al Cu The relationship is linear if the following conditions are fulfilled: Hext is homogeneous and isotropic The conductivity of the sample is not too high and the parasitic field ~ external field R sample and R magnet < wavelength of the field A phase shift between M and H exists and is 90 deg

29 Eddy currents depend on the radius of the sample h = 8 mm, 10 mm d 2 mm Eddy currents keep constant with the height of the sample d = 4 mm, 10 mm h 2 mm

30 m is proportional to dh/dt linear

31 Local eddy current measurements Al and Cu discs h = 5 mm d = 5; 11; 18; 26; 35 mm At the inner position (Mi) the eddy current loops agreed with the results of Kuepferling et al for d < 12 mm

32 Conclusions 1- It was demonstrated that a high impedance pick-up coil is quite sensitive to small capacitance variations and noise, what limit ist application in a pulsed field magnetometer. Nevertheless, the high impedance does not affect the shape of the loop if the pick-up coils system is well compensated. 2- It was demonstrated the calibration of the local area magnetization measurements in physical units, when the samples have the same volume. 3- The local area measurements are very sensitive to the sample s geometry, what allows using them as a tool for the quality control in the industrial production of permanent magnets.

33 4- It was obtained the local demagnetizing factor for samples with different dimensions, and it was demonstrated the possibility of performing study of the homogienity of the magnetization along the radius of the sample. It was also demonstrated experimentally, that the theoretical value of Nm is an approximation only valid at the center of the sample. 5- It was demonstrated the possibility of performing transverse susceptibility measurements in a PFM. We are unaware of any previous attempt. 6- It has been demonstrated that a PFM is, in many instances, an indispensable instrument for the characterization of magnetic materials in the laboratory as well as in the industry.

New sensors for measuring M and H in high magnetic fields

Physica B 346 347 (004) 543 547 New sensors for measuring M and H in high magnetic fields J.H. Espina-Hern!andez a,b, *, R. Gr.ossinger a, S. Kato a,c, H. Hauser d, E. Est!evez-Rams b a Institute of Solid