MAGNETIC BUBBLE APPARATUS

Popis novih vježbi koje bi se uvele na Praktikumu čvrstog stanja, opreme koju je potrebno kupiti i postojeće opreme prikladne za te vježbe Promatranje feromagnetskih domena i mjerenje M-­‐H krivulja Pomoću transmisijskog prikaza kroz polarizator se optički razlučuju feromagnetske domene posebno dizajniranog uzorka, te ovisnost veličine domena variranjem vanjskog magnetskog polja. Smještanjem optički osjetljivog otpornika na okular mikroskopa se može mjeriti ovisnost intenziteta prolazne (polarizirane) svjetlosti o magentskom polju. Na taj način se efektivno promatra ovisnost magnetizacije o magnetkom polju, te određuju krivulje histereze. Postojeća oprema: • Mikroskop s kamerom i USB priključkom (iz laboratorija prof. Požeka) • ampermetar Potrebna oprema: • Tel-­‐A magnetic bubble apparatus 227$ = 178 EUR • Optički osjetljiva dioda x5 5x21,5 kn =107.5 kn • +6V – 1A izvor, za kontrolu magnetskog polja • potenciometar MAGNETIC BUBBLE APPARATUS
Lab experiments can be performed to let you demonstrate:
MAGNETIC BUBBLE
APPARATUS TEL-300
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Magnetic domains in a Ferrimagnetic garnet (FMG).
Formation of magnetic bubbles.
The Barkhausen effect.
Plotting of hysteresis loops.
In 1908 Weiss proposed his domain theory to explain the magnetic properties of materials. It is for these kinds
of experiments that this apparatus has been developed.
Principle
In the search for magnetic materials which could be used for bubble memories, Bobeck discovered that
ferrimagnetic garnets (FMG) could be "engineered" to produce the very small, isolated cylindrical domains
(called bubbles because of the end-on shape when viewed) which were stable yet capable of being formed,
moved and destroyed at very high rates.
To achieve the correct orientation of the FMG it has to be grown on the face of another single crystal of similar
lattice size. In this way both the magnetic and optical properties can be controlled.
The material in this apparatus has the formula Bi0.6Tm2.4Ga1.15 Fe3.85O12 and is about 8um thick and transparent.
Accessories required for viewing:
Microscope (x100 magnification); Low ripple power supply - 6 VDC, 1 amp or battery; Ammeter;
Potentiometer; Light dependent resistor (for plotting hysteresis loops).
Typical views as seen through a microscope X100
magnification
REMNANT STATE WITH EQUAL
AREAS OF EACH DOMAIN.
MAGNETIZING FIELD 0.00 HSAT.
FIELD 0.77 HSAT.
FIELD 0.95 HSAT.
FIELD 0.99 H SAT. NOTE THE
"BUBBLES"
Faraday Effect
Materials are magnetic because of the anisotrophy and this in turn means there is interaction between the
electrons when any electromagnetic radiation passes through. The resulting effect is to rotate the plane of
vibration of the radiation — the so-called Faraday effect. Thus the plane of polarized light entering such a
medium will be rotated. The amount of rotation depends on path length and the amound of interaction —
optical activity.
The film of FMG is transparent and yellow in unpolarised light, but when viewed through crossed Polaroids, the
pattern of the domains becomes visible in the unmagnetised remnant state or a striped (serpentine) form. To
view the domain patterns a microscope of about x100 magnification is needed.
Forming Bubbles
If the FMG is maintained in a static transverse magnetizing field, bubbles can be produced by small local
changes in the field.
SIDE VIEW OF MAGNETIC BUBBLE
Plotting M-H Loops
Graphs can be plotted from measurements of the magnetization M of the material resulting from a
magnetizing field of strength. In general, M will follow H up to saturation but not necessarily linearly. After
saturation, M remains constant with increasing H. What happens to M when H is reduced to zero and
eventually reversed depends on the nature of the material.
In the unmagnetised state FMG contains equal volumes of both kinds of domains, and when an external
magnetizing field H is applied, magnetization occurrs by the growth of one domain at the xpense of the others.
The intensity of light transmitted through FMG is proportional to the magnetization M, so by using a photo cell
a measure of M can be obatined. Since the magnetic field H is directly proportional to the current in the coil
producing it, M-H loops can be plotted.
Each Magnetic Domain includes:
Magnetic bubble apparatus constructed with solid brass body containing a wire coil of 300 turns; Connector
plug with hookup wire; Complete experiment instructions.
Accessories required for viewing:
Microscope (x100 magnification); Low ripple power supply - 6 VDC, 1 amp or battery; Ammeter;
Potentiometer; Light dependent resistor (for plotting hysteresis loops).
Mjerenje faznog prijelaza uzorka s magnetskim uređenjem Mjerenje temperaturne ovisnosti susceptibilnosti (mjerenjem induciranog napona) uzorka s magnetskim uređenjem na temperaturama iznad 77 K (Dy, Tb, Gd, CuO2 i sl.) kako bi se promotrio magnetski fazni prijelaz. Postojeća oprema: • dewar kapaciteta 10 l (iz laboratorija prof. Požeka), • sonda za mjerenje susceptibilnosti (iz laboratorija prof. Požeka), • računalo (staro, no u radnom stanju, iz računalne učionice) Potrebna oprema: • Lock-­‐in pojačalo, 3300 EUR • Pt senzor x2 500 kn • Zaštitna oprema (rukavice, naočale) 150 kn • Sirovine za poboljšanje sonde, <2000 kn • GPIB -­‐2-­‐USB (Keithley, 528$) 412 EUR Mjerenje faznog prijelaza uzorka s nabojnim uređenjem Mjerenje temperaturne ovisnosti električnog kapaciteta gdje je kao dielektrik korišten uzorak s nabojnim uređenjem (BaTiO3, KH2PO4, KD2PO4, NaKC4H4O6...) na temperaturama iznad 77 K (Dy, Tb, Gd, CuO2 i sl.) kako bi se promotrio električni fazni prijelaz. Postojeća oprema: • dewar kapaciteta 10 l (iz laboratorija prof. Požeka) • električni krug za marginalni oscilator • Frekvenc-­‐meter (iz laboratorija prof. Požeka) • računalo (staro, no u radnom stanju, iz računalne učionice) Potrebna oprema: • Zaštitna oprema (rukavice, naočale) 150 kn • Sirovine za poboljšanje sonde, <2000 kn • Napajanje 20 V – 1 A • Pt senzor x2, 500 kn • Sonda za mjerenje, <2000kn • GPIB -­‐2-­‐USB (Keithley, 528$) 412 EUR Mjerenje kutne ovisnosti magnetootpora monokristala Bi Cilj vježbe je studentima omogućiti zorni prikaz Fermijeve plohe te ovisnosti njene simetrije o detaljima kristala. Mjerenjem kutne ovisnosti magnetootpora monokristalnog Bi studenti mogu vidjeti kako ono ima karakterističnu simetriju koja nije određena geometrijom uzorka već intrinzičnim svojstvima elektronskih orbitala Postojeća oprema: • Mala dewarica kapaciteta s izoliranim (iz laboratorija prof. Požeka) • Elektromagnet • Strujni izvor • Nanovoltmetar Potrebna oprema: • Bi monokristal 420 GBP = 525 EUR • Potrošni materijal za postavljanje kontakata na uzorak + Sirovine za poboljšanje postava kako bi se dobro definirala kutna ovisnost <2000 kn Promatranje staklastog prijelaza mjerenjem viskoznosti Pomoću postava za mjerenje torzije rotacije osovine u tekućem uzorku (glicerol) mjeri se viskoznost kako se temperatura uzorka smanjuje preko prijelaza u staklasto stanje. Postojeća oprema: • Mala sonda za mjerenje torzije (iz laboratorija prof. Požeka) • Ampermetar • Voltmetar • Naponski izvor • Termos boca Potrebna oprema: • Pt senzor 250 kn • Potrošni materijal za doradu sonde + elektromotor <2000 kn Ukupno (okvirno): 11657 kn + 4830 EUR; cca 48376 kn