Anisotropic Transport Properties of Complex Metallic Alloys

Anisotropic transport properties (electrical resistivity, ρ, and thermal conductivity, κ) of the Y-phase Al-Ni-Co, o-Al13Co4 and Al4(Cr,Fe) complex metallic alloys were investigated. They belong to the class of decagonal approximant phases with stacked-layer crystallographic structure and allowed us to study the evolution of anisotropic transport properties with increasing structural complexity and the unit cell size.</p

Hall Coefficient of the Y-Al-Ni-Co Decagonal Approximant

We have investigated anisotropic Hall coefficient of Y-Al-Ni-Co decagonal approximant of the Al76Co22Ni2 composition. The crystalline-direction-dependent studies were performed along three orthogonal directions a*, b and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Hall coefficient RH exhibits pronounced anisotropy, while at the same time the magnetic field in a given crystalline direction yields the same RH for the current along the other two crystalline directions in the perpendicular plane. The observed anisotropy is studied in terms of the anisotropic structure of the Y-Al-Ni-Co phase and Fermi surface. The results are compared to the anisotropy of the Hall coefficient of the d-Al-Ni-Co decagonal quasicrystal reported in literature.</p

Anisotropic Transport Properties of the Al13Fe4 Decagonal Approximant

We have investigated electrical resistivity, thermoelectric power and thermal conductivity of the Al13Fe4 monoclinic approximant to the decagonal quasicrystal. The crystallographic-direction-dependent measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The electronic transport exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The anisotropic thermopower reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like contributions.</p

Magnetic memory effect in multiferroic K3Fe5F15 and K3Cr2Fe3F15

The fluorides K3Fe5F15 and K3Cr2Fe3F15 are known as multiferroic materials. Here we report the detection of a magnetic memory effect in these materials and its dependence on temperature and aging time. We succeeded in writing, reading, and deleting 3-bits digital information in these systems. These results show that in addition to their already known magneto-electric multiferroic properties, K3Fe5F15 and K3Cr2Fe3F15 also possess a new functionality: they can be used as materials for a thermal memory cell

Toplinska vodljivost fazno-dijagramskih bliznaca Al-Cr-Fe

We have investigated electrical resitivity and thermal conductivity of quasicrystalline compounds of the Al-Cr-Fe system: a gamma-brass phase (γ-AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O1/O2-AlCrFe) with properties which are in many respects intermediate to regular metals and quasicrystals. The electrical resistivities show very weak temperature dependence and the resistivity values are in between regular metals and aluminum-based quasicrystals. Thermal conductivity data show that the electronic and lattice contributions are of comparable size. While the electronic contribution can be described by the Wiedemann–Franz law, the lattice contribution can be reproduced by a sum of a long-wavelength phonons and hopping terms. At the lowest measured temperature, scattering of phonons on stacking-fault-like defects limits the heat transport. This type of defects has also been observed in the structural investigations. The results indicate that transport properties of quasicrystalline approximants are not determined by the short-range atomic order only, but are affected by both, the short-range quasiperiodic and long-range periodic atomic orders.Istraživali smo električnu otpornost i toplinsku vodljivost kvazikristalnih spojeva sustava Al-Cr-Fe: γ-fazu (γ-AlCrFe) i smjesu dvaju ortorombskih faznodijagramskih bliznaca dekagonalne faze (O1/O2-AlCrFe) čija su svojstva u mnogim pogledima između običnih metala i kvazikristala. Električne otpornosti pokazuju vrlo slabu temperaturnu ovisnost i njihove su vrijednosti između onih običnih metala i kvazikristala na osnovi aluminija. Podaci o toplinskoj vodljivosti pokazuju da su doprinosi elektrona i rešetke podjednaki. Elektronski doprinos može se opisati Wiedemann–Franzovim zakonom, a doprinos rešetke zbrojem doprinosa dugovalnih fonona i članova od preskakanja. Na najnižoj temperaturi mjerenja, raspršenje fonona na nepravilnostima rešetke sličnima defektima u slaganju atoma, ograničuje vođenje topline. Ta je vrsta nepravilnosti opažena i u istraživanjima strukture. Rezultati pokazuju da transportna svojstva kvazikristalnih bliznaca nisu određena samo kratko-dosežnom atomskom strukturom, već ovise i o kratko-dosežnim kvaziperiodičnim i o dugodosežnim periodičnim atomskim strukturama

Hall Effect of the Al13Fe4 Decagonal Approximant and Its Ternary Extension Al13(Fe,Ni)4

We have measured Hall coefficient and electrical resistivity of the Al13Fe4 and Al13(Fe,Ni)4 monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary extension Al13(Fe,Ni)4 contains quenched disorder and can be viewed as a disordered version of Al13Fe4. The crystallographic-direction-dependent Hall effect measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The stacking b direction is the most conducting direction for the electricity. The effect of quenched disorder in Al13(Fe,Ni)4 is manifested in the large residual resistivity ρ(T → 0) as compared to the ordered Al13Fe4. The Hall coefficient, RH, values for all combinations of directions, are typical metallic. The anisotropic Hall coefficient reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like parts. Depending on the combination of directions of the current and magnetic field electron-like (RH 0) contributions may dominate, or the two contributions compensate each other (RH ≈ 0).</p

The Influence of Thermal Treatment on Magnetic Moments in i-Al-Pd-Mn Quasicrystals

The influence of cooling rate on thermal strains in the quasicrystalline icosahedral Al-Pd-Mn complex metallic alloy was investigated. In general, measurements of the electronic magnetization can be used as an indirect method for determining the short-scale disorder in the crystal structure as the magnetic moments at the Mn sites are highly dependent on their local environment. Excluding the contributions of thermal vacancies and second phase precipitates by proper selection of preannealing temperatures and durations, the changes in magnetization can be ascribed to the appearance or disappearance of thermal strains in the crystal structure. It was found that water-quenching increases thermal strains irrespective of previous thermal history.</p

Phonon-enhanced thermoelectric power of Y-Al-Ni-Co decagonal approximant

We have investigated anisotropic electrical resistivity andthermoelectric power of the ypsilon-phase Al-Ni-Co (Y-Al-Ni-Co)decagonal approximant with composition Al(76)Co(22)Ni(2). Thecrystalline-direction-dependent measurements were performed along threeorthogonal directions a*, b and c of the Y-Al-Ni-Co unit cell, where(a, c) monoclinic atomic planes are stacked along the perpendicular bdirection. Anisotropic electrical resistivity is low in all crystallinedirections, appearing in the order rho(a*) &gt; rho(c) &gt; rho(b) andshowing positive temperature coefficient typical of electron-phononscattering mechanism. Thermopower shows electron-phonon enhancementeffect. Anisotropic bare thermopower (in the absence of electron-phononinteractions) was extracted, appearing in the same order as theresistivity, vertical bar S(a*)(bare)/T vertical bar &gt; vertical barS(c)(bare)/T vertical bar &gt; vertical bar S(b)(bare)/T vertical bar

Toplinska vodljivost fazno-dijagramskih bliznaca Al-Cr-Fe

We have investigated electrical resitivity and thermal conductivity of quasicrystalline compounds of the Al-Cr-Fe system: a gamma-brass phase (γ-AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O1/O2-AlCrFe) with properties which are in many respects intermediate to regular metals and quasicrystals. The electrical resistivities show very weak temperature dependence and the resistivity values are in between regular metals and aluminum-based quasicrystals. Thermal conductivity data show that the electronic and lattice contributions are of comparable size. While the electronic contribution can be described by the Wiedemann–Franz law, the lattice contribution can be reproduced by a sum of a long-wavelength phonons and hopping terms. At the lowest measured temperature, scattering of phonons on stacking-fault-like defects limits the heat transport. This type of defects has also been observed in the structural investigations. The results indicate that transport properties of quasicrystalline approximants are not determined by the short-range atomic order only, but are affected by both, the short-range quasiperiodic and long-range periodic atomic orders.Istraživali smo električnu otpornost i toplinsku vodljivost kvazikristalnih spojeva sustava Al-Cr-Fe: γ-fazu (γ-AlCrFe) i smjesu dvaju ortorombskih faznodijagramskih bliznaca dekagonalne faze (O1/O2-AlCrFe) čija su svojstva u mnogim pogledima između običnih metala i kvazikristala. Električne otpornosti pokazuju vrlo slabu temperaturnu ovisnost i njihove su vrijednosti između onih običnih metala i kvazikristala na osnovi aluminija. Podaci o toplinskoj vodljivosti pokazuju da su doprinosi elektrona i rešetke podjednaki. Elektronski doprinos može se opisati Wiedemann–Franzovim zakonom, a doprinos rešetke zbrojem doprinosa dugovalnih fonona i članova od preskakanja. Na najnižoj temperaturi mjerenja, raspršenje fonona na nepravilnostima rešetke sličnima defektima u slaganju atoma, ograničuje vođenje topline. Ta je vrsta nepravilnosti opažena i u istraživanjima strukture. Rezultati pokazuju da transportna svojstva kvazikristalnih bliznaca nisu određena samo kratko-dosežnom atomskom strukturom, već ovise i o kratko-dosežnim kvaziperiodičnim i o dugodosežnim periodičnim atomskim strukturama