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Magnetocrystalline anisotropy of Ni-Mn-Ga-Co-Cu martensite
Rameš, Michal ; Straka, Ladislav ; Sozinov, A. ; Heczko, Oleg
The martensites of Heusler alloys based on Ni-Mn-Ga exhibit magnetically-induced reorientation resulting in giant field-induced strain. Up to 12% strain was observed in Ni-Mn-Ga-Co-Cu with 4 at.% of Co and Cu. The driving force of the phenomenon is the magnetocrystalline anisotropy. We studied evolution of the anisotropy with temperature and compositions using magnetiyation curve measurements in four different single crystalline Ni-Mn-Ga-Co-Cu and compared with non-doped Ni-Mn-Ga. The anisotropy of martensite decreases with increasing average doping (Co+Cu)/2 but it does not scale with tetragonal ratio or valence electron concentration.
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Ground state investigations of Ce and U intermetallic compounds
Bartha, Attila ; Prokleška, Jan (advisor) ; Detlefs, Blanka (referee) ; Michor, Herwig (referee)
Title: Ground state investigations of Ce and U intermetallic compounds Author: Attila Bartha Department: Department of Condensed Matter Physics Supervisor: RNDr. Jan Prokleška, Ph.D., Department of Condensed Matter Physics Abstract: Rare earth and actinide intermetallic compounds offer a plethora of interesting physical properties due to the varied behavior of f -electrons together with numerous interactions these electrons are exposed to. In this thesis we address a broad spectrum of ground state investigations on CePd2X3 (X=Zn, Ga) and (Ce,U)nTIn3n+2 (T=Rh, Ir) compounds. Single crystals of CePd2Zn3 and CePd2Ga3 compounds were synthesized for the first time using Bridgman method. CePd2Ga3 revealed a ferromagnetic transition with TC = 6.7 K with a strong magnetocrystalline anisotropy. CePd2Zn3 orders antiferromagnetically below TN = 1.9 K. Results of magnetization measurements on Ce2IrIn8 revealed effective magnetic moment µeff = 2.45µB/Ce3+ and a paramagnetic Curie temperature θP = −31 K. Decomposition of Hall resistivity ρxy(B) into NHE and AHE revealed a predom- inance of AHE in the temperature range from 60 K up to 100 K. Ce2RhIn8 was studied by means of magnetic field and angle dependent magnetization and heat capacity measurements. The resulting phase diagram reveals a complete unfold- ing and...
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Relaxivity of magnetic iron oxide nanoparticles containing diamagnetic cations
Kubíčková, Lenka ; Kohout, Jaroslav (advisor) ; Chlan, Vojtěch (referee)
Magnetic nanoparticles have received extensive attention in the biomedical research, e.g. as prospective contrast agents for T2-weighted magnetic resonance imaging. The ability of a contrast agent to enhance the relaxation rate of 1 H in its vicinity is quantified by relaxivity. The main aim of this thesis is to evaluate the transversal re- laxivity of ε-Fe2−x Alx O3 nanoparticles coated with amorphous silica or citrate - its dependence on external magnetic field, temperature and thickness of silica coating - by means of nuclear magnetic resonance. The aluminium content x = 0.23(1) was determined from XRF, the material was further characterised by XRPD, Möss- bauer spectroscopy, DLS, TEM and magnetic measurements. The size of magnetic cores was ∼ 21 nm, the thickness of silica coating ∼ 6,10,17 and 21 nm. Magne- tization of the ε-Fe2−x Alx O3 nanoparticles increased by ∼ 30 % when compared to ε-Fe2O3. The saturating dependence of relaxivity on external magnetic field and on the linear decrease with increase of thickness of silica coating contravene the theo- retical model of motional averaging regime (MAR); nevertheless, the temperature dependence acquired in 0.47 T and 11.75 T may be explained by MAR. In compari- son to ε-Fe2O3 nanoparticles, the relaxivity of examined samples was higher for par-...
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