Magnetism in RMn4Al8 (R=Sc, Sm, Tb, Dy and Ho) compounds: possible role of Mn
TL;DR: In this paper, the AC magnetic susceptibility, electrical resistivity and thermoelectric power results of RMn 4 Al 8 compounds are discussed and the magnetism in these compounds can be explained in terms of the Mn site occupancy and the Mn-Mn distances along c -axis.
Abstract: The AC magnetic susceptibility, electrical resistivity and thermoelectric power results of RMn 4 Al 8 compounds are discussed. The compounds with magnetic rare earths order antiferromagnetically at low temperatures. Electrical transport is dominated by electron–phonon scattering at high temperatures. The magnetism in these compounds can be explained in terms of the Mn site occupancy and the Mn–Mn distances along c -axis.
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TL;DR: In this article, the authors investigated the bulk properties, elastic properties and Debye temperature under pressure, and deformation mode under tension of Al8Cu4Y and Al8Cr4Y compounds by using first principles calculations based on density functional theory.
Abstract: An investigation into the bulk properties, elastic properties and Debye temperature under pressure, and deformation mode under tension of Al8Cu4Y and Al8Cr4Y compounds was investigated by using first principles calculations based on density functional theory. The calculated lattice constants for the ternary compounds (Al8Cu4Y and Al8Cr4Y) are in good agreement with the experimental data. It can be seen from interatomic distances that the bonding between Al1 atom and Cr, Y, and Al2 atoms in Al8Cr4Y are stronger than Al8Cu4Y. The results of cohesive energy show that Al8Cr4Y should be easier to be formed and much stronger chemical bonds than Al8Cu4Y. The bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν can be obtained by using the Voigt–Reuss–Hill averaging scheme. From the results of elastic properties, Al8Cr4Y has the stronger mechanical behavior than Al8Cu4Y. Our calculations also show that pressure has a greater effect on mechanical behavior for both compounds. The ideal tensile strength are obtained by stress-strain relationships under [001](001) uniaxial tensile deformation, which are 15.4 and 23.4 GPa for Al8Cu4Y and Al8Cr4Y, respectively. The total and partial density of states and electron charge density under uniaxial tensile deformations for Al8Cu4Y and Al8Cr4Y compounds are also calculated and discussed in this work.
13 citations
TL;DR: In this paper, the crystallographic and magnetic properties of solution grown RMn{sub 2+x}Al{sub 10-x} (R=Gd and La) crystals with tetragonal (P4/nmm) structure are investigated.
Abstract: The crystallographic and magnetic properties of the solution grown RMn{sub 2+x}Al{sub 10-x} (R=Gd and La) crystals with tetragonal (P4/nmm) structure are investigated. For these, single-crystal x-ray diffraction results have shown the preferential occupation of excess manganese on the aluminum 8i crystallographic site. Due to excess Mn, there is evidence of local-moment magnetism in LaMn{sub 2+x}Al{sub 10-x} and their random distribution is thought to be responsible for the magnetic correlations below {approx}50 K and the spin-glass behavior below {approx}3 K. For GdMn{sub 2+x}Al{sub 10-x}, the extra manganese influences temperature below which the sample enters into a state with a net ferromagnetic component: T{sub C}{approx_equal}16 K for GdMn{sub 2.21(4)}Al{sub 9.79(4)} and 25.5 K for GdMn{sub 2.39(2)}Al{sub 9.61(2)}. Assuming a linear dependence between T{sub C} and excess Mn concentration, the fully stoichiometric and ordered GdMn{sub 2}Al{sub 10} should have T{sub C}{approx_equal}5 K.
7 citations
TL;DR: In this paper, single crystal x-ray diffraction data confirmed the orthorhombic structure of rare-earth rhenium aluminide and showed that all compounds have effective moments close in value to that of free Rhenium-aluminide at high temperatures.
Abstract: Large single crystals of rare-earth rhenium aluminide $R{\text{Re}}_{2}{\text{Al}}_{10}$, with $R=\text{Y}$, and Gd--Lu were grown out of an Al-rich solution. Single crystal x-ray diffraction data confirmed the orthorhombic $Cmcm$ structure for all members: $R=\text{Gd-Dy}$ with $\text{Tb}{\text{Re}}_{2}{\text{Al}}_{10}$-structure type (formula unit per cell $Z=8$); $R=\text{Y}$, and Ho--Lu with ${\text{LuRe}}_{2}{\text{Al}}_{10}$-structure type $(Z=12)$. There is no evidence of a localized $3d$ electron moment in $R=\text{Y}$ and Lu; $R=\text{Yb}$ is nonmagnetic down to 1.8 K, but develops an enhanced electronic specific heat of $\ensuremath{\sim}95\text{ }\text{mJ}\text{ }{\text{mol}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$. Ordering temperatures range from ferromagnetic order in $R=\text{Gd}$ with ${T}_{\text{c}}=7.2(1)\text{ }\text{K}$, antiferromagnetic order in $R=\text{Tb}$ at ${T}_{\text{N}}=5.0(3)\text{ }\text{K}$, to $R=\text{Dy}$, Ho, and Er giving magnetic ordering temperatures of ${T}_{\text{mag}}=1.7(1)$, $\ensuremath{\le}0.4$, and 1.1(2) K, respectively. All compounds have effective moments close in value to that of free ${R}^{3+}$ at high temperatures.
6 citations
TL;DR: In this paper, the isothermal section of phase diagram of the Ho-Mn-Ti ternary system at 773 K has been investigated mainly by X-ray powder diffraction analysis with the aid of differential thermal analysis.
Abstract: The isothermal section of phase diagram of the Ho–Mn–Ti ternary system at 773 K has been investigated mainly by X-ray powder diffraction analysis with the aid of differential thermal analysis in this work. The existence of eight binary compounds HoMn 2 , Ho 6 Mn 23 , HoMn 12 , Mn 5 Ti, Mn 2 Ti, βMnTi, αMnTi and Mn 15 Ti 85 has been confirmed in this system. At 773 K, the maximum solid solubility of Ti in αMn is about 8 at.%Ti. The homogeneity range of Mn 2 Ti extends from about 31 at.% to 39 at.% Ti. The maximum solid solubility of Ho in Mn 2 Ti phase is about less than 1 at.% Ho. The existence of solid solubility of other phases was not observed. No ternary compounds were found in this ternary system. At 773 K, the isothermal section of phase diagram of Ho–Mn–Ti ternary system consists of 11 single-phase regions, 19 two-phase regions and 9 three-phase regions.
2 citations
TL;DR: In this paper, the authors report results of magnetic studies of glass-forming alloys with nominal composition of Al86Gd6TM8 (where TM = {Cu, Ni, Co, Fe, Mn, Cr, Ti, Zr, Mo, Ta} synthesized by arc-melting.
Abstract: We report results of magnetic studies of glass-forming alloys with nominal composition of Al86Gd6TM8 (where TM = Cu, Ni, Co, Fe, Mn, Cr, Ti, Zr, Mo, Ta) synthesized by arc-melting. X-ray diffraction analysis and vibrating sample magnetometry were applied to characterize the prepared samples. All the alloys exhibit antiferromagnetic ordering at low temperatures. In some compositions, we observed metamagnetic transitions in external magnetic fields up to 3 T. Analysis of the paramagnetic susceptibility of the considered Al-Gd-TM systems has revealed non-magnetic behavior of the transition metals. We found that the magnetic properties of the studied samples can be described satisfactorily using only the Gd trivalent ions. But in some cases the magnetic moments of gadolinium are slightly larger than the theoretical values, probably, because of an additional contribution of the 5d electrons. The obtained results are discussed in framework of the assumptions of the strong s-p-d hybridization and frustrated magnetic states of gadolinium. We argue that the hybridization might be one of the main factors improving the glass-forming ability in these ternary alloys.
2 citations
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TL;DR: Mossbauer and magnetic susceptibility studies of sixty tetragonal RM 4 Al 8 compounds (R = 4 f, M = 3 d element), show a wide variety of magnetic phenomena in the behaviour of 3 d transition elements.
Abstract: Mossbauer and magnetic susceptibility studies of sixty tetragonal RM 4 Al 8 compounds ( R = 4 f , M = 3 d element), show a wide variety of magnetic phenomena in the behaviour of 3 d transition elements. The rare earths order antiferromagnetically at temperatures below 10–30 K in all compounds. The 3 d elements, however, all behave differently. Fe in R Fe 4 Al 8 has a localized moment (effective moment of 4.4 μ B ) and orders independently of the rare earth sublattice. Mn in R Mn 4 Al 8 has also a localized moment (∼1 μ B ) but orders only when the rare earths order. Cr in R Cr 4 Al 8 has no moment of its own, but it has an induced moment (.1 μ B ) by its magnetic rare earth neighbours. Cu in R Cu 4 Al 8 is nonmagnetic. The Mossbauer studies of 151 Eu, 155 Gd, 161 Dy, 166 Er, 170 Yb and a 57 Fe probe yield all hyperfine interaction parameters including the orientation of the hyperfine field relative to the crystallographic c -axis. In addition, the studies yield the Ce, Eu and Yb valencies in the various compounds. Eu in EuFe 4 Al 8 and in EuMn 4 Al 8 and Yb in YbCr 4 Al 8 are in a mixed valent state.
93 citations
TL;DR: In this article, specific heat measurements have been performed on the tetragonal ThMn 12 -type RMn 4 Al 8 compounds with R=Y, La, Pr, Nd, Dy, and Er in the temperature range 1.5 to 200 K.
Abstract: Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RMn 4 Al 8 compounds with R=Y, La, Pr, Nd, Dy and Er in the temperature range 1.5 to 200 K. The compound PrMn 4 Al 8 gives rise to a λ-type anomaly at 14 K. No anomalies indicative of magnetic ordering were found above 1.5 K in the specific-heat curves of the RMn 4 Al 8 compounds with R=Y, La, Nd, Dy, and Er. From the temperature dependence of the magnetic entropy, it is concluded that the overall crystal-field splitting in the compounds with R=Pr, Nd, Dy, and Er is of the order of 200 K or even less.
38 citations