Rare-earth Sublattice Research Articles

Pressure effect on electrical resistivity of [formula omitted

Electrical resistivity of Y 1 - x Gd x Co 2 alloy system has been measured at temperatures from 2 to 300 K in magnetic field up to 15 T and under pressure up to 10 GPa. The compounds with the composition near to phase boundary between paramagnetic and ferromagnetic ground state ( x c ≈ 0.12 ) show strong enhancement of electrical resistivity at low temperatures. Large positive magnetoresistance was observed in ferromagnetic alloys in composition range 0.15 < x < 0.3 . The anomalous magnetoresistance as well as the composition dependence of the low-temperature resistivity were explained by an interplay of metamagnetic instability of Co 3d itinerant electrons and structural disorder within rare-earth sublattice. The pressure effect on electrical resistivity for Y 1 - x Gd x Co 2 at low temperatures is in agreement with the variation of magnetoresistance with the composition.

Effect of rare-earth doping inRCrSb3(R=La, Pr, Sm, and Gd)

We report on the electrical resistivity and magnetic susceptibility of La or Gd doped $R{\mathrm{CrSb}}_{3}$ ($R=\mathrm{La}$, Pr, Sm, and Gd). Single crystals were grown by increasing the nominal dopant by 25%. In general, two magnetic ordering transitions are found, ${T}_{c1}$ is attributed to ferromagnetic ordering of the itinerant Cr sublattice, and, at lower temperatures, ${T}_{c2}$ is attributed to ordering of the localized rare-earth sublattice. Alloying on the rare-earth site varies the de Gennes factor, $\mathrm{DG}={(g\ensuremath{-}1)}^{2}J(J+1)$, and $d{T}_{c1}∕d(\mathrm{DG})=\ensuremath{-}2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, while $d{T}_{c2}∕d(\mathrm{DG})=5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These ordering temperatures are found to converge at ${\mathrm{GdCrSb}}_{3}$, where a single ferrimagnetic transition is found at ${T}_{c2}=86\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ due to an antialignment of the itinerant Cr magnetic sublattice and the localized rare-earth magnetic sublattice. Initially, for $\mathrm{DG}&lt;3.5$, the two magnetic sublattices order in a ferromagnetic ground state, and the paramagnetic Weiss temperature decreases at the same rate as ${T}_{c1}$. But for $\mathrm{DG}&gt;4.5$, the rare-earth magnetic sublattice antialigns with respect to the Cr sublattice, and the Weiss temperature decreases five times as fast. In the region between $(3.5&lt;\mathrm{DG}&lt;4.5)$, a first-order phase transition is found at ${T}_{c2}$.

An analysis of the hyperfine parameters of theRFe11Ti and RFe11TiH compounds, where R is a rare-earth element

The Mössbauer spectra of CeFe11Ti and CeFe11TiH obtained between 4.2 and 295 K are analysed in terms of the model used to analyse the spectra of theRFe11Ti and RFe11TiH compounds, where R is Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Lu. The hyperfine parametersobtained with a consistent model that considers both the easy magnetization direction andthe titanium preferential site occupancy are discussed as a function of rare-earth atomicnumber, temperature and hydrogen content. The average hyperfine fields in theRFe11Ti and RFe11TiH compounds are described with a two-sublattice model in which theiron sublattice contributions coincide with the fields observed inLuFe11Ti and LuFe11TiH, respectively. In both series, the rare-earth sublattice contributes a transferredfield which occurs as a result of indirect exchange between the rare-earth 4f andiron 3d electrons and depends on the nature of the rare-earth element. Theincrease in average hyperfine field and isomer shift upon hydrogenation of theRFe11Ti compounds results from the unit-cell expansion upon hydride formation. The observedaverage quadrupole shift is closely related to the magnetic anisotropy exhibited by eachcompound.

Magnetic behavior in Ce1–xTbxMn2Si2 silicides by XRD, DSC and AC susceptibility measurements

AbstractThe structural and magnetic properties the polycrystalline Ce1–xTbxMn2Si2 (0 ≤ x ≤ 1) compounds were studied by means of X‐ray powder diffraction, AC susceptibility and differential scanning calorimetry (DSC). All compounds investigated crystallize in the body‐centred tetragonal ThCr2Si2‐type structure with the space group I4/mmm. Substitution of Tb for Ce leads to a linear decrease of the lattice constants and the unit cell volume. The lattice constants and the unit cell volume obey Vegard's law. At low temperatures, the rare earth sublattice orders and reconfigures the ordering in the Mn sublattice for x ≥ 0.2. The Néel temperature TN(Mn) determined by DSC technique increases linearly with increasing Tb content x. The results are collected in the x–T magnetic phase diagram. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Magnetic properties of Tb 1−xSm xMn 2Si 2 silicides

The structural and magnetic properties of polycrystalline Tb 1− x Sm x Mn 2Si 2 ( 0 ⩽ x ⩽ 1 ) compounds were studied by means of X-ray powder diffraction, AC susceptibility and differential scanning calorimetry (DSC). All compounds investigated crystallize in the body-centred tetragonal ThCr 2Si 2-type structure with the space group I4/mmm. Substitution of Sm for Tb leads to a linear increase of the lattice constants and the unit cell volume. The lattice constants and the unit cell volume obey Vegard's law. At low temperatures, the rare earth sublattice orders and reconfigures the ordering in the Mn sublattice. The Néel temperature T N(Mn) determined by DSC technique decreases linearly with increase in Sm content x. The results are collected in an x– T magnetic-phase diagram.

Spontaneous magnetostriction in R 2Fe 14B (R=Y, Nd, Gd, Tb, Er)

Thermal expansion anomalies of R 2Fe 14B (R=Y, Nd, Gd, Tb, Er) stoichiometric compounds were studied by X-ray diffraction with high-energy synchrotron radiation using a Debye–Scherrer geometry in temperature range of ∼10–1000 K. A large invar effect with a corresponding large temperature dependence of lattice parameters ∼10–15 K above their Curie temperatures ( T c) are observed. The a-axes show a larger invar effect than the c-axes in all compounds. The spontaneous magnetostrain of the lattices and bonds are calculated. The iron sublattice is shown to dominate the volumetric spontaneous magnetostriction of the compounds and the contribution from the rare-earth sublattice is roughly proportional to the spin magnetic moment of the rare earths. The bond-length changes are consistent with the theoretical spin-density calculation. The average bonds magnetostrain around Fe sites is approximately proportional to their magnetic moments.

Effect of Hydrogenation on the Magnetic and Magnetoelastic Properties of the Tb[sub 0.27]Dy[sub 0.73]Fe[sub 2] and Tb[sub 0.27]Dy[sub 0.73]Co[sub 2] Compounds with Compensated Magnetic Anisotropy

The effect of hydrogenation on the magnetic ordering temperature and magnetostriction of the Tb0.27Dy0.73Fe2 and Tb0.27Dy0.73Co2 compounds with compensated magnetic anisotropy of the rare-earth sublattice was studied. It was established that the incorporation of hydrogen atoms into the crystal lattice of the compounds studied lowers the Curie temperature. It is shown that, in this case (i.e., for structures of the Laves phase type), the decrease in T C results primarily from the change in the electronic structure of these compounds. An anomaly was found in the temperature dependence of thermal expansion of Tb0.27Dy0.73Co2 and its hydride. It was established that hydrogenation brings about a substantial weakening of magnetostriction, which should be attributed to a change in the local electronic density induced by the incorporation of hydrogen atoms into the crystal lattice.

Structural and magnetic properties of the new R 2Li 2Si 3 compounds (R = La, Ce, Pr, Nd, Sm)

The R 2Li 2Si 3 compounds, with R = La, Ce, Pr, Nd and Sm, synthesized and structurally studied by powder and single crystal X-ray diffraction, belong to the Ce 2Li 2Ge 3 orthorhombic type. The magnetization and heat capacity data show the occurrence of normally trivalent cerium ions in Ce 2Li 2Si 3 ordering ferromagnetically at 17 K. Pr 2Li 2Si 3 becomes antiferromagnetic at 18 K, its isothermal magnetisation at 1.8 K showing a field induced spin flip transition at 25 kOe. For Nd 2Li 2Si 3 the transition to the antiferromagnetic state occurs at 9.5 K. Two peaks are seen in the heat capacity data of Ce 2Li 2Si 3 and Nd 2Li 2Si 3 which can be attributed to either two symmetry inequivalent rare earth sublattices ordering at different temperatures or to spin re-orientation.

Magnetism on the Tb 1−xNd xMn 2Si 2 silicides

The structural and magnetic properties of the polycrystalline Tb 1− x Nd x Mn 2Si 2 (0⩽ x⩽1) compounds were studied by means of X-ray powder diffraction, AC susceptibility and differential scanning calorimetry (DSC). All compounds investigated crystallize in the body-centered tetragonal ThCr 2Si 2-type structure with the space group I4/mmm. Substitution of Nd for Tb leads to a linear increase of the lattice constants and the unit cell volume. The lattice constants and the unit cell volume obey Vegard's law. At low temperatures, the rare-earth sublattice orders and reconfigures the ordering in the Mn sublattice. The samples with x=0.2, x=0.4 and x=0.6 exhibit spin reorientation phenomenon below T C(RE) and at about 200 K, AC susceptibility curve of these samples has a cusp denoting the Néel temperature T N1(Mn). The Néel temperature T N2(Mn) determined by DSC technique decreases linearly with increasing Nd content x. The results are collected in the x– T magnetic phase diagram.

A comparative study on magnetostrictive strain in GdCo 5 and Gd 0.9 Pr 0.1 Co 5

Results of the magnetostriction measurements on exchange coupled GdCo5-type alloys, (with insignificant magnetic anisotropy of L-quenched Gd+3 ions) show lower values compared to Gd0.9Pr0.1Co5 compound. In fact, partial substitution of Pr for Gd creates an orbital moment for the rare earth sublattice and therefore the magnetocrystalline anisotropy (MA) increases. The temperature dependence of MA introduces the spin reorientation transition in Gd0.9Pr0.1Co5 compound. Simple model calculations indicate that a negative contribution in the first order anisotropy constant (K1) appears after Pr substitution. The sign of K1 changes from negative to positive at ∼160 K with increasing temperature. The latter introduces a large increase in the anisotropic magnetostriction. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic and magnetoelastic properties of the TbMnSi and Tb0.5La0.5MnSi compounds

X-ray diffraction studies showed substitution of nonmagnetic lanthanum for terbium in the TbMnSi polycrystalline compound to initiate a structural transition from a TiNiSi-type orthorhombic structure (for TbMnSi) to a CeFeSi-type tetragonal phase (for Tb0.5La0.5MnSi). Magnetic measurements (of the magnetization, magnetostriction, thermal expansion) performed on Tb0.5La0.5MnSi revealed a change in the character of magnetic ordering, the appearance of a ferromagnetic component in the Mn magnetic moment, a strong increase in magnetization as compared to TbMnSi, and the appearance of a spontaneous magnetic moment. Insertion of the lanthanum ion onto the rare-earth sublattice of TbMnSi brings about a change in the unit cell size and, hence, in the Mn-Mn, Mn-Si, and R-Mn interatomic distances, which causes, in turn, a change in the character of exchange interactions in Tb0.5La0.5MnSi and the formation of a complex magnetic structure.

Rare-earth orbital contribution to the FeK-edge x-ray magnetic circular dichroism in rare-earth transition-metal intermetallic compounds

We present a systematic x-ray magnetic circular dichroism (XMCD) study performed at the Fe K-edge of the RFe 1 1 Ti intermetallic materials (R, rare earth). We have investigated the contribution of the rare-earth sublattice to the dichroism of the transition metal. The existence of a magnetic contribution of the rare earth has been identified and isolated from the whole spectrum. This contribution is found to be related to the rare-earth moment even when one is looking at the Fe K-edge absorption. The contribution of the rare earths to the total XMCD signal has been extracted for both pure and hydride derivatives, showing the decrease of the rare-earth magnetic moment upon hydrogen absorption.

Magnetic structures of R 3Cu 4Sn 4 (R=Tb–Er)

Neutron powder diffraction studies of the R 3Cu 4Sn 4 (R=Tb, Dy, Ho, Er) intermetallic compounds with the orthorhombic Gd 3Cu 4Ge 4-type crystal structure indicate the existence of different magnetic structures. Rare earth atoms occupy two nonequivalent 2d and 4e sublattices. For R=Tb and Dy the magnetic structures below the Néel temperatures equal to 17.5 and 15 K, respectively, are described by the propagation vectors k =(0,0, 1 2 +δ). In these compounds both rare earth sublattices order and do not change up to the Néel temperatures. For R=Ho the magnetic structure is more complicated. There are two vectors; one of them is k =(0, 1 2 ,0) whereas the second one changes with temperature. For the Er compound there is the propagation vector k =( 1 2 , 1 2 ,0) which describes the magnetic ordering in the 2d sublattice and at low temperatures it is accompanied with the propagation vector k =(0,0,δ) describing the ordering in the 4e sublattice.

Magnetic ordering and irreversible magnetization between ZFC and FC states in RCo 5Ga 7 compounds

The magnetic properties of RCo 5Ga 7 (R=Y, Tb, Dy, Ho and Er) compounds which crystallize in the ScFe 6Ga 6-type structure have been studied. The compounds with R=Y, Tb, Dy, Ho and Er display behaviour similar to semiconductors. The Co transition metal sublattice is ferrimagnetic with a very low spontaneous magnetization. The ferrimagnetic ordering observed for R=Y, Tb, Dy, Ho and Er is due to the transition metal sublattice with transition temperatures at about 295 K. At low temperatures, the magnetic ordering for R=Tb, Dy, Ho and Er is due to the rare-earth sublattice, which is ferromagnetic with a Curie temperature below 5 K. By fitting the linear part of the inverse magnetization, the effective magnetic moment of the R ion is found to be close to its expected theoretical value, with paramagnetic Curie temperatures below 5 K. Due to the paramagnetic nature of the R sublattice above 60 K, the ferrimagnetic ordering temperature of the Co sublattice does not vary with the type of rare-earth ion. The irreversibility of the magnetization of YCo 5Ga 7, as measured in zero-field cooled (ZFC) and field cooled (FC) states, is attributed to movement of domain walls. Application of a large enough applied field completes the movement of the domain wall from the low-temperature to the high-temperature one at 5 K. With a very low magnetic field 100 Oe, the difference between the ZFC and the FC shrinks.

Magnetic Neutron Scattering from the Rare-Earth Intermetallic Compound System R&lt;sub&gt;3&lt;/sub&gt;Pd&lt;sub&gt;20&lt;/sub&gt;Si&lt;sub&gt;6&lt;/sub&gt; (R = Rare Earth)

The low-temperature magnetic properties of the rare-earth intermetallic compound system R3Pd20Si6 (R = rare earth) were studied by elastic and inelastic neutron scattering. The compounds show due to the two rare-earth sublattices built from the 4a and 8c sites in the cubic crystal structure (space group Fm-3m) successive magnetic ordering with two different propagation vectors. In this report, we give an overview of the results obtained for the magnetic structures and the crystalline electric fields in the 3-20-6-system.

XMCD study of RFe11Ti intermetallic compounds

Abstract We present a systematic X-ray Magnetic Circular Dichroism (XMCD) study performed at the Fe K-edge of the RFe 11 Ti intermetallic materials. We have investigated the contribution of the rare-earth sublattice to the dichroism of the transition metal. The existence of a magnetic contribution of the rare-earth has been identified and isolated from the whole spectrum. This contribution is found to be related to the rare-earth moment even when one is looking at the Fe K-edge absorption.

Magnetic properties of Pr1−xGdxMn2Ge2

The structural and magnetic properties ofPr1−xGdxMn2Ge2 were studied by x-ray diffraction and magnetization measurements. The substitution of Gdfor Pr leads to a linear decrease in the lattice constants and the magnetic interactions inthe Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one.At low temperatures, the rare-earth sublattice also orders and reconfigures the ordering inthe Mn sublattice. The spins in the Mn sublattice are arranged parallel to the Pr sublatticeand antiparallel to the Gd sublattice. The results are collected in a phase diagram.

Magnetic properties of Pr 1− xGd xMn 2Ge 2 compounds

The structure and magnetic properties of the Pr 1− x Gd x Mn 2Ge 2 (0.0≤ x≤1.0) compounds have been investigated by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements. All compounds crystallize in the ThCr 2Si 2-type structure with the space group I4/ mmm. The lattice constants and the unit cell volume obey Vegard’s law. Samples in this alloy system exhibit a crossover from ferromagnetic ordering for PrMn 2Ge 2 to antiferromagnetic ordering for GdMn 2Ge 2 as a function of Gd concentration x. At low temperatures, the rare earth sublattice also orders and reconfigures the ordering in the Mn sublattice. The results are summarized in the x– T magnetic phase diagram.

AC susceptibility, XRD and DSC studies of Sm 1− xGd xMn 2Si 2 silicides

X-ray powder diffraction, AC susceptibility and differential scanning calorimetry (DSC) studies were performed on the polycrystalline Sm 1− x Gd x Mn 2Si 2 (0⩽ x⩽1) compounds. All compounds investigated crystallize in the body-centered tetragonal ThCr 2Si 2-type structure with the space group I4/mmm. Substitution of Gd for Sm leads to a linear decrease of the lattice constants and the unit cell volume. The lattice constants and the unit cell volume obey Vegard's law. At low temperatures, the rare earth sublattice orders and reconfigures the ordering in the Mn sublattice. The samples with x=0.6 and 0.8 exhibit spin reorientation phenomenon. The Néel temperature T N(Mn) determined by DSC technique and the Curie temperature T C (RE) increase linearly with increasing Gd content x. The results are summarized in the x− T magnetic phase diagram.

Magnetic ordering of R3Cu4Sn4(R = Tb,Dy, Ho and Er)

Neutron diffraction studies of polycrystalline R3Cu4Sn4(R = Tb,Dy, Ho, Er) intermetallic compounds with the orthorhombic Gd3Cu4Ge4-typecrystal structure indicate the existence of different magnetic structures.Rare earth atoms occupy two non-equivalent 2d and 4e sublattices. Therare earth magnetic moments order at low temperatures. For R = Tband Dy the magnetic structures below the Néel temperature are describedby the propagation vectors k = (0, 0, 1/2 + δ).In these compounds both rare earth sublattices order. For R = Ho themagnetic structure is more complicated. There are two vectors; one of them is k = (0, 1/2, 0)whereas the second one changes with temperature. For the Ercompound there is the propagation vector k = (1/2, 1/2, 0)which describes the magnetic ordering in the 2d sublattice and at lowtemperatures is accompanied by the propagation vector k = (0, 0,δ)describing the ordering in the 4e sublattice.