AC Measurement of Magnetic Susceptibility. Physics 401, Fall 2016 Eugene V. Colla

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1 AC Measurement of Magnetic Susceptibility Physics 41, Fall 216 Eugene V. Colla

2 Outline Ferromagnetism Measurement of the magnetic properties of the materials Lab experimental setup and experiments Some results 11/7/216 2

3 Ferromagnetism. Definition. Some materials below a certain temperature (Tc) give rise to the magnetic field in absence of an applied field. This magnetization is called spontaneous, the phenomenon ferromagnetism and materials exhibiting this feature ferromagnetics. The main parameter of the ferromagnetic phase transition is spontaneous magnetization M s (T)/M s () 1..5 Typical behavior of spontaneous magnetization as function of temperature T/Tc 11/7/216 3

Aleksandr Stoletov (1839 1896) Stoletov curve dm dh MnSb 587 MnOFe 2 O * 3 573 Y 3 Fe 5 O * 12 56 CrO

4 Ferromagnetic materials. Material Curie temp. (K) Co 1388 Fe 143 Fe 2 O 3 * 948 FeOFe 2 O 3 * 858 NiOFe 2 O 3 * 858 MgOFe 2 O 3 * 713 MnBi 63 Ni 627 Aleksandr Stoletov ( ) Stoletov curve dm dh MnSb 587 MnOFe 2 O * Y 3 Fe 5 O * CrO MnAs 318 Gd 292 Stoletov performed pioneer works in area of ferromagnetic materials but better known by his research in photoelectric effect. 11/7/216 4

5 Domains. Hysteresis loop. M~M s M= * Courtesy Wikipedia 11/7/216 5

6 Domains Several grains of NdFeB with magnetic domains made visible via contrast with a Kerr microscope. Courtesy of Wikipedia Kerr microscope Courtesy of University of Uppsala (Sweden) 11/7/216 6

7 Domains Moving domain walls in a grain of silicon steel caused by an increasing external magnetic field Courtesy of Wikipedia 11/7/216 7

8 Hysteresis Loops. Remagnetization loses Energy of the magnetic field W = V න HdB By cycling around the loop W loop = V HdB=V*Loop_area 11/7/216 8

9 Hard materials. Application. RAM memory Permanent magnets Hard drives, floppy, magnetic tape 11/7/216 9

10 Soft materials. Application. Chokes, inductors Power transformers 11/7/216 1

11 Magnetic Field, Susceptibility etc. B H M B magnetic induction M magnetization, in general M(H) M H χ magnetic susceptibility, in general χ(h) B H H H 1 r r 1 db r ; r dh 1 db dh 11/7/216 11

12 Modulation Spectroscopy B f ( H ) H = H + H1sinωt df B = f(h ) + (H1sinωt) +... dh H 1 =const B B w B f ( H) B ω ~ db dh H = H + H1sinωt H 11/7/216 12

the B-H hysteresis loop or dependence of the magnetic

13 Measuring the magnetic permeability By applying a small modulation of the H field we can measure the derivative of the B-H hysteresis loop or dependence of the magnetic permeability on H field ( H, w) (1 ( H, w)) db dh H, w 11/7/216 13

14 Setup #1. Investigation of the hysteresis loops. 11/7/216 14

15 Setup #1. Investigation of the hysteresis loops. H = N pi p 2πr H H H 1 coswt 11/7/216 15

16 H(a.u.) Major/minor loops. Demagnetization 1 B saturation time H -1 Waveform of H-field 11/7/216 16

17 B (a.u.) Demagnetization 3.6 Demagnetization of 4C65 toroid from Ferroxcube I DC (A) 1 Idc(A) time (min) time (min) 11/7/216 17

18 Hysteresis Loops Fig. A family of AC hysteresis loops for grain-oriented electrical steel (B R denotes remanence and H C is the coercivity). Courtesy Zureks (Wikipedia) 11/7/216 18

19 Measuring the magnetic permeability max ~ I DC (A) time (s) '/ DC current profile and magnetic permeability of Magnetics ZW44715TC H (A/m) H (A/m) 11/7/216 19

20 From permeability to B-H hysteresis loop ECE storeroom unknown material Sample #5 Step#1. Performing one fast IDC scan the based on the result preparing the smart IDC profile IDC (A) 1-1 Step#2. Performing precise scan the. Plotting raw data based time (s) Voltage units measured by SR83 Y (mv) Current in primary coil in A I DC (A) 11/7/216 2

21 From permeability to B-H Step#3. What we are measuring? Calibration. Lock-in measures emf on the pickup coil hysteresis loop d Vlock in ; B S dt Here Ip is ac current in primary coil L3; I p = V sin(ωt) R 2 11/7/216 21

22 From permeability to B-H hysteresis loop Step#3. What we are measuring? Calibration. Primary coil of N p turns supplied by current I p creates magnetic field H and flux dφ For toroid: H = N pi p 2πr R 2 <r < R 1 R2 I N t dr I N t R2 H da ln 2 da=dr*t r 2 R R 1 d 1 11/7/216 22

23 From permeability to B-H hysteresis loop Step#3. What we are measuring? Calibration. Total flux detected by pickup coil: N pickup d N pickupn pi p t R ln 2 R 2 1 Np and Ip number of turns of AC primary coil and AC rms current Inductance of the toroid: L ; L r L ( i ) L I L N N t R ln 2 R pickup p /7/216 23

24 From permeability to B-H hysteresis loop di p Vlock in r L dt Y (mv) 1..8 ' I DC (A) H (A/m) H = N pi DC 2πr 11/7/216 24

From permeability to B-H hysteresis loop ' 6 5 4 3 Step#4.

25 From permeability to B-H hysteresis loop ' Step#4. From r (H) to B-H db ( H ) ( H ) H dh r H (A/m) After integrating B(T). B( H ) ( H ) dh r H (A/m) 11/7/216 25

26 Software issue Icon on the desktop Preparation of the profile of the experiment 2nd week experiment B-H measurement 1 st week experiment Demagnetization 11/7/216 26

27 Software issue Measuring profile preparation. Using profile template Open a new file Create a new file Save prepared file for future use

28 Software issue Measuring profile preparation. Using profile template.

29 Software issue Measuring profile preparation Example of simple protocol Advanced profile ' H (A/m)

30 Software issue Measurement Window Lock-in amplifier response The profile of the applied DC current Structure of the data file (B-H experiment)

$Data analysis using Origin To calculate the permeability better to use the template : \\engr-file-3\phyinst\apl Courses\PHYCS41\Common\Origin$

31 Data analysis using Origin To calculate the permeability better to use the template : \\engr-file-3\phyinst\apl Courses\PHYCS41\Common\Origin templates\ac magnetic Lab\MU_CALCULATION.otw It does not contain the equations you have to write them Raw data Parameters Calculated results 11/7/216 31

32 Data analysis using Origin. Integrating. B( H ) ( H ) dh r 11/7/216 32

33 Data analysis using Origin. Integrating. B( H ) ( H ) dh offset r M s -M s 11/7/216 33

34 References Information about magnetic materials can be found in : \\engr-file-3\phyinst\apl Courses\PHYCS41\Experiments\AC_Magnetization\Magnetic Materials SR83 manual: \\engr-file-3\phyinst\apl Courses\PHYCS41\Common\EquipmentManuals\SR83m.pdf 11/7/216 34

AC Measurement of Magnetic Susceptibility. Part 2. Physics 401, Spring 2015 Eugene V. Colla

AC Measurement of Magnetic Susceptibility. Part 2. Physics 401, Spring 2015 Eugene V. Colla Outline What and how we measuring (week1) Magnetic looses Temperature dependencies of permeability End of semester