Utjecaj magnetskog polja na modul elastičnosti nekih krutina

undergraduate thesis

• Title (english): Influence of magnetic field on elasticity module of some solids
• Author: Dario Tomić
• Mentor: Vladimir Dananić (mentor)
• Committee member: Vladimir Dananić (predsjednik povjerenstva)
• Committee member: Zvonimir Glasnović (član povjerenstva)
• Committee member: Miroslav Jerković (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2017-09-20, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics; General and Classical Physics

Abstract

Različiti materijali ponašaju se na različite načine, kada se na njih djeluje nekim vanjskim magnetskim poljem. Kod paramagnetika, dijamagnetika i feromagnetika dolazi do magnetizacije, koja nije kod svih jednaka. Do najsnažnije magnetizacije dolazi kod feromagneta jer je kod njih prisutna pojava spontane magnetizacije, odnosno materijal posjeduje magnetizaciju i prije nego što se podvrgne magnetskom polju. Magnetski momenti spontano se raspodjele u različite regije koje se nazivaju domene, a koje su međusobno odijeljene tzv. domenskim zidom. Možemo reći da feromagneti imaju svoje vlastito unutarnje magnetsko polje. Kod dijamagneta i paramagneta, ne dolazi do spontane magnetizacije, nego je magnetizacija prisutna samo kada na njih djeluje vanjsko magnetsko polje. Svaki feromagnet sa svojim svojstvima ovisi o temperaturi; do određene temperature svaki feromagnet će zadržati svoja svojstva. Granična temperatura nakon koje se gube feromagnetska svojstva i gdje dolazi do paramagnetskog ponašanja, naziva se Curieva temperatura; kod svakog feromagneta je ona različita. Pod utjecajem magnetskog polja, dolazi do pojave koja se naziva magnetostrikcija. Zbog magnetostrikcije odnosno promjene u magnetizaciji feromagneta, dolazi do deformacije. Mijenja se Youngov modul elastičnosti; ta promjena može biti pozitivna odnosno dolazi do produljenja materijala; te negativna, gdje dolazi do sabijanja materijala. Kod slabijih magnetskih polja treba uzeti u obzir i anizotropiju odnosno anizotropnu energiju koja nije zanemariva kao što je to slučaj kod jakih magnetskih polja, u kojima ona nema utjecaja. Anizotropija nastaje kao posljedica međudjelovanja atoma u strukturi feromagneta; zbog različite orijentacije prilikom magnetizacije, nisu u cijeloj strukturi materijala jednaka svojstva. Važno je spomenuti i petlju histereze koja nam govori da procesi magnetizacije i demagnetizacije nisu reverzibilni odnosno magnetska indukcija se ne mijenja jednakim intenzitetom kao i magnetsko polje. U eksperimentalnom dijelu promatrana su dva eksperimenta koje su radili renomirani znanstvenici, a koji su pokazivali različite ovisnosti Youngova modula elastičnosti o temperaturi, jakosti magnetskog polja i magnetizaciji. Primjećeno je da se Youngov modul najviše mijenja pod utjecajem jakih magnetskih polja te pri temperaturama nižim od Curieve. Što je temperatura niža, to je i magnetizacija manja.

Abstract (english)

Different materials act differently when they are exposed to outer magnetic field. Paramagnetics,diamagnetics and ferromagnetics don't have the same magnetization. The strongest magnetization is present at ferromagnets because before they are influenced by the magnetic field, they show the effect of spontainuous magnetization. Magnetic moments spontainuously divide themselfs into different regions which are called the domains. We can say that ferromagnetics have their own inner magnetic field. Paramagnetics and diamagnetics don't have the effect of spontainuous magnetization, magnetization is present only when they are influenced by outer magnetic field. Each ferromagnet and their properties are related to temperature; they will keep their properties within a certain temperature range. The temperature where they lose their properties and where they act like paramagnets is called the Curie temperature; different ferromagnets have different Curies temperature. Under the influence of magnetic field the effect of magnetostriction can appear. Because of the magnetostriction which is basically the change of the magnetization in ferromagnets, the appearance of deformation can occure. Youngs module of elasticity is changing itself; that change can be positive or negative. Positive change is when materials are being extended and negative when they are being compressed. In the presence of weaker magnetic fields we must also consider the anisotropy and anisotopic energy which can't be ignored as there is such a case in strong magnetic fields. Anisotropy appears as a consequence of atomic interactions in ferromagnetic structure; because of the different orientation at magnetization, there aren't the same properties in the whole volume. It's vital to mention the hysteresis loop which is telling us that the processes of magnetization and demagnetization are not reversibile; magnetic induction is not changing with the same intensity as the magnetic field. In experimental part, two experiments were observed which were made by the renowned scientists and which were showing us different influences on Youngs elasticity module by temperature, power of magnetic field and magnetization. It was sighted that Youngs module has the biggest change under the influene of strong magnetic fields and at the temperatures lower than Curies. Lower magnetization is at lower temperatures.

• Keywords: feromagnetizam; Curieva temperatura; Youngov modul elastičnosti; magnetostrikcija; anizotropija; petlja histereze; magnetska domena; domenski zid
• Keywords (english): ferromagnetism; Curies temperature; Youngs module of elasticity; magnetostriction; anisotropy; hysteresis loop; magnetic domain; domain wall
• Language: croatian
• URN:NBN: urn:nbn:hr:149:888194
• Study programme: Title: Environmental Engineering - Undergraduate study; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka ekoinženjerstva (sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka ekoinženjerstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2021-03-15 12:26:43