Ordering Of Mn Sublattice Research Articles

Interplay of two magnetic sublattices in related compounds Sm2Mn1-xGa6-yGey (x = 0.1-0.3, y = 0.6-1.0) and Sm4MnGa12-yGey (y = 3.0-3.5) with different ordering of empty and filled (Ga,Ge)6 octahedra.

Single crystals of two new intermetallic phases Sm2Mn1-xGa6-yGey (x = 0.1-0.3, y = 0.6-1.0) and Sm4MnGa12-yGey (y = 3.0-3.5) were grown using a self-flux technique. According to single crystal X-ray diffraction data, Sm4MnGa12-yGey is characterised by the Y4PdGa12 structure type (a ∼ 8.65 Å; Im3̄m), while Sm2Mn1-xGa6-yGey formally adopts the K2PtCl6 structure type (a ∼ 8.71 Å; Fm3̄m). The general features of both compounds with rather similar crystal structures are represented by the alternation of empty and Mn-filled p-element octahedra, the order of which is determined by the Mn concentration. The diffraction data for Sm2Mn1-xGa6-yGey reveal a large concentration of Mn vacancies (x ∼ 0.3), which affects adjacent Ga/Ge atoms leading to their shift towards the vacancy. Both compounds demonstrate two ferromagnetic-like transitions and the presence of two interacting Mn and Sm magnetic sublattices. The Mn sublattice orders at TC1 of 143 K and 318 K, while the Sm one orders at lower temperatures at TC2 of 50 K and 280 K for Sm4MnGa8.6Ge3.4 and Sm2Mn0.74Ga5.1Ge0.9, respectively. The increase in Mn content not only increases the ordering temperatures, but also dramatically decreases the coercivity μ0HC from 230 mT to just 6.5 mT at 2 K. Despite the presence of two magnetically active sublattices in Sm2Mn0.74Ga5.1Ge0.9, the magnetic entropy change is quite low and only reaches 0.3 J kg-1 K-1 at T = 300 K and μ0H = 5 T, while the estimated relative cooling power (RCP) is about 36 J kg-1 at 5 T.

Crystal growth and magnetic properties of LaMn0.91Sb2 and NdMn0.88Sb2

In this work, single crystals of ${\mathrm{LaMn}}_{0.91}{\mathrm{Sb}}_{2}$ and ${\mathrm{NdMn}}_{0.88}{\mathrm{Sb}}_{2}$ with deficiencies of Mn have been successively grown by using the Bi-flux method. They all crystallize in the ${\mathrm{HfCuSi}}_{2}$-type tetragonal structure with space group $P4$/nmm (No.129). ${\mathrm{LaMn}}_{0.91}{\mathrm{Sb}}_{2}$ displays signs of successive antiferromagnetic transitions around 133 and 108 K for $H||c$. In the case of $H\ensuremath{\perp}c$, ${\mathrm{LaMn}}_{0.91}{\mathrm{Sb}}_{2}$ shows signs of weak ferromagnetic transition around 138 K and antiferromagnetic transition at 56 K. However, there is no anomaly observed in the temperature-dependent specific heat curve. For ${\mathrm{NdMn}}_{0.88}{\mathrm{Sb}}_{2}$ measured with $H||c$, the Mn sublattice orders antiferromagnetically below 170 K and the Nd sublattice shows successive antiferromagnetic orders at 34 and 26 K. The antiferromagnetic state of Nd sublattice can be induced to be a ferromagnetic state through a spin-flop transition at 2 K. When $H\ensuremath{\perp}\mathrm{c}$, the Mn sublattice displays antiferromagnetic orders at 171, 156, and 74 K. The Nd sublattice orders antiferromagnetically below 32 K. Ferromagnetic state for the Nd sublattice is induced by magnetic fields through a spin-flop transition at 2 K. Magnetic phase diagrams for ${\mathrm{NdMn}}_{0.88}{\mathrm{Sb}}_{2}$ are depicted for cases of $H||c$ and $H\ensuremath{\perp}c$, respectively. ${\mathrm{LaMn}}_{0.91}{\mathrm{Sb}}_{2}$ and ${\mathrm{NdMn}}_{0.88}{\mathrm{Sb}}_{2}$ show metallic behavior. Negative magnetoresistance in ${\mathrm{LaMn}}_{0.91}{\mathrm{Sb}}_{2}$ and ${\mathrm{NdMn}}_{0.88}{\mathrm{Sb}}_{2}$ are possibly related to canted-antiferromagnetic orders of Mn sublattices.

Simultaneous magnetic and structural transitions in Nd0.15Ca0.85MnO3 manganite: Magnetization and neutron diffraction studies

The manganite Nd0.15Ca0.85MnO3 crystallizes in GdFeO3-type, orthorhombic structure (space group Pnma) at 300 K and orders antiferromagnetically at 112 K (TN). Magnetization-field (M-H) isotherms indicate metamagnetic transition at temperatures below TN. However, metamagnetism does not lead to saturation in magnetization. The magnetization value at 2 K in 140 kOe field is only 0.4 μB/f.u. The isothermal magnetic entropy change (ΔSm) has been calculated using the M-H data and inverse magnetocaloric effect is observed around TN and the maximum value of ΔSm is ∼12.2 J kg−1K−1 at 107.5 K for 140 kOe field change. Powder neutron diffraction study in zero applied field reveals monoclinic distortion of Nd0.15Ca0.85MnO3 crystal lattice and antiferromagnetic ordering of Mn sublattice in ac-plane with wave vector K = [1/2, 0, 1/2] at 125 K. From the neutron data, the Mn magnetic moment value at 3 K is found to be 2.54 μB. Electrical resistivity increases tremendously below TN to an insulating state and shows thermal hysteresis near TN in zero field. Large magnetic fields drive insulator to metal-like transition and negative colossal magnetoresistance of about 70% is realized at 50 K in 70 kOe field and that could be due to the field-induced order.

Structure and magnetic properties of layered compounds RMn1.7Cr0.3Si2C (R = Nd, Sm, Dy)

The carbon doped RMn1.7Cr0.3Si2C (R = Nd, Sm, Dy) compounds were prepared by arc melting and investigated using room temperature (RT) X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetic measurements. Carbon atoms were found to occupy the interstitial site (0, 0, 0.125) in a superstructure with the space group P4/mmm at room temperature. There exists a disordered substitution between the R atoms and corresponding Si dumbbells on the same layer perpendicular to c direction in the carbides. The Mn/Cr sublattice of the carbides exhibits ferromagnetic characteristics at room temperature despite of a very short intralayer interatomic distance (dMn-Mn = 2.796 Å for R = Dy), which is far below the critical distance for a ferromagnetic (dMn-Mn >2.87 Å) ordering of Mn sublattice due to the strong hybridization between the interstitial C and the Mn/Cr atoms. Different phase transitions of the carbides have different response to the external magnetic field. These carbides provide the potential for further research on magneto-transport properties and magnetocaloric effect. Additionally, spin reorientation was observed in SmMn1.7Cr0.3Si2C owing to the competence of magnetocrystalline anisotropy between the Mn/Cr sublattice and the Sm sublattice.

Magnetic ordering in intermetallic [formula omitted] compounds

The magnetic structures and magnetic phase transitions in intermetallic layered La1-xTbxMn2Si2 compounds (the ThCr2Si2-type structure) are investigated using the first-principles method and XPS measurements. The experimentally observed transition from ferromagnetic (FM) to antiferromagnetic (AFM) ordering of Mn sublattice with increase of terbium concentration is successfully reproduced in calculations for collinear magnetic moments model. The FM→AFM change of interplane magnetic ordering at small x is irrelevant to the number of f-electrons of the rare-earth ion. In contrast it was shown to be related to the Mn-Mn in-plane distance. Calculated Tb critical concentration for this transition x≈0.14 corresponds to the Mn-Mn in-plane distance 0.289 nm, very close to the experimentally observed transition distance 0.287 nm. The crystal cell compression due to substitution increases an overlap between Mn dxz,yz and the rare-earth ion d orbitals. Resulting hybridized states manifest themselves as an additional peak in the density of states. We suggest that a corresponding interlayer Mn-R-Mn superexchange interaction stabilizes AFM magnetic ordering in these compounds with Tb doping level x>0.2. The results of DFT calculations are in agreement with X-ray photoemission spectra for La1-xTbxMn2Si2.

Neutron diffraction study of Tb0.5Ho0.5Mn2Si2

The magnetic properties of tetragonal polycrystalline intermetallic compound Tb0.5Ho0.5Mn2Si2 have been investigated using temperature dependent dc magnetic susceptibility and neutron powder diffraction studies. Results of high temperature susceptibility data shows anomaly at TN=510K while low temperature susceptibility data indicate two successive anomalies at T1=11K and T2=25K. Metamagnetic transition is observed in magnetization versus field curves. Our neutron diffraction results indicate three different magnetic regions with different magnetic structures. Neutron diffraction data shows that below T2, the intensities of some of the nuclear peaks get enhanced indicating ferromagnetic ordering, while additional magnetic reflections are observed below T1, indicating antiferromagnetic order. Ordering of rare earth sublattice at low temperature rearranges the ordering of Mn sublattice and results in reorientation of Mn spins at T1. At 2KTb/Ho moments are aligned along c-axis while Mn moments are aligned perpendicular to c-axis.

Structural and magnetic study of PrMn1–xFexO3 compounds

The structural and magnetic study of PrMn1−xFexO3 (0 ≤ x ≤ 1) substitutional orthorhombical system, was performed on polycrystalline (x ≤ 0.5) as well as on the single crystalline (0.5 ≤ x) samples. In this system the orthorhombic to orthorhombic structural phase transition takes place at high temperatures for x ≤ 0.2 due to long range ordering of 3d3x2−r2 and 3d3y2−r2 Mn orbitals in Jahn-Teller distorted structure. We have found the Jahn-Teller distortion still contributes to orthorhombic distortion of the crystal lattice for samples with x ≤ 0.6 at room temperature. Our investigation of the magnetic phase transition with respect to chemical composition revealed the crossover region 0.4 ≤ x ≤ 0.5 in which both Fe and Mn long range magnetic ordering exist simultaneously and the magnetic ordering of Mn sublattice is induced by already ordered Fe sublattice. The spin reorientation magnetic phase transitions are typical features for samples with 0.6 ≤ x. We have not found any traces of magnetic ordering of Pr ions at temperatures higher than 2 K. These results enable us to construct complex structural and magnetic phase diagram for PrMn1−x FexO3 system.

Grain size effect on magnetic properties of REMnO3 (RE = Pr, Nd)

X-ray diffraction and magnetic using dc and ac methods measurements of the polycrystalline and nanosize REMnO3 (RE = Pr, Nd) powdered samples have been performed. The nanosize manganites were synthesized with a sol-gel method at different (800, 850 and 900 °C) temperatures. The average size of synthesized nanoparticles (from 56 to 89 nm) and polycrystalline powders (above 200 nm) was estimated using the x-ray diffraction data. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature with smaller values of the lattice parameters in the nanosamples. The temperature-dependent ac magnetic susceptibilities show a sharp high-temperature peak connected with Mn magnetic moments ordering. The low-temperature maximum of magnetic susceptibility is proposed to be due to the polarization of the rare-earth sublattice by an effective exchange field of the Mn ordered sublattice. The antiferromagnetic ordering of Mn sublattice and paramagnetic Curie temperatures as well as the magnetic moment values for the nanosize samples was found to be smaller than those for polycrystalline sample.

Magnetic properties of NdMn1-xFexO3+δsystem

Magnetization, AC susceptibility and specific heat measurements were performed on polycrystalline NdMn1-xFexO3+δ compounds (x = 0.0, 0.1 and 0.2). Substitution of Fe for Mn reduces the Néel temperature TN, which is associated with magnetic ordering of Mn sublattice, from 85.5 K to 57.0 K. The temperature dependence of magnetization for x = 0.2 exhibits the compensation temperature and the pole inversion below Tcomp = 26.7(5) K. Initial magnetization curves present a remnant magnetization in the ordered region with the sign of remnant magnetization depending on temperature. The substitution of Fe for Mn changes hysteresis loop of NdMnO3+δ from the ferromagnetic-like one (μ0Hc = 0.09 T) by expanding the width of the loop (μ0Hc = 0.55 T) for x = 0.1 and then shrinking the central part of the loop to “butterfly” type (μ0Hc = 0.35 T) for x = 0.2.

Magnetic properties and magnetocaloric effect in intermetallic compounds NdMn2−xCoxSi2

We report magnetic properties and magnetocaloric effect in intermetallic compounds NdMn2−xCoxSi2 (x = 0.2, 0.4, 0.6, 0.8, and 1). dc magnetization study shows that these compounds undergo a ferromagnetic-like transition at around 45 K. Neutron diffraction study at 5 K for the x = 0.2 sample shows a canted-ferromagnetic state at lower temperature (5 K), and a collinear antiferromagnetic state at higher temperature (above ∼50 K). At 5 K, the Nd moments are aligned along the crystallographic c-axis and the Mn moments are canted to the c-axis. At higher temperatures (50, 100, 200, and 300 K), Nd sublattice does not order but Mn sublattice orders antiferromagnetically. A magnetocaloric effect (MCE) is found with a magnetic entropy change of 14.4 and 12.4 J kg−1 K−1 for the x = 0.2 and 0.4 samples, respectively, at 47.5 K under a field variation of 50 kOe. Various interesting phenomena such as metamagnetic transitions and domain wall pinning have been observed, and their role in obtaining a large MCE and an inverse MCE, respectively, has been brought out. The hysteresis (in magnetic field dependent dc magnetization study) reduces significantly at temperatures near and above the magnetic transition temperature (TC), which makes these materials important for their practical applications in magnetic refrigeration around TC.

Magnetic and magnetocaloric properties of R 6Mn 23 (R=Y, Nd, Sm, Gd-Tm, Lu) compounds

The magnetic and magnetocaloric properties of the R 6Mn 23 compounds (R=Y, Nd, Sm, Gd-Tm, Lu) are investigated from DC magnetization measurements. The results are analyzed and discussed in connection with previously published data. These binaries crystallize in the cubic Th 6Mn 23 type of structure (Fm-3m). The Mn sublattice orders at high temperature (398 K≤ T C≤505 K) with a collinear ferrimagnetic structure. The R sublattice orders at lower temperature (<100 K) with a non-collinear arrangement. By opposition with the usual behaviour in intermetallics, light rare-earth compounds (R=Nd and Sm) have a lower ground state magnetization than the heavy rare-earth compounds (R=Gd-Tm). This manifests in their magnetocaloric response near the R ordering temperature: the compounds with R=Gd-Tm display a normal magnetocaloric effect of moderate magnitude (<50 mJ cm −3 K −1 for a field variation of 5 T) while those with R=Nd and Sm present an inverse magnetocaloric effect of weaker magnitude. The potential interest of these phases for cooling applications is briefly discussed.

Exchange-induced Tm magnetism in multiferroic h-TmMnO3

Analysis of 169Tm Mössbauer spectra recorded for (hexagonal phase) h-TmMnO3 confirms that the Mn sublattice orders magnetically below TNMn = 82–83 K and reveals the growth of a local Tm moment at the 4b site that is induced by theMn–Tm exchange interaction. The maximum hyperfine field recorded at the 169Tm nucleus is 312 T, which is just under half of the free ion value and corresponds to a saturation momentof 3.29 µB. The temperature dependence of the fitted magnetic hyperfine interactionis closely represented by a simple two-singlet ground state model for theTm3+ crystal field scheme. The saturation molecular field is deduced to lie in the rangeBMn−Tm(T = 0 K) = 1.2–2.3 T, dependent on the expectation value of the couplingα = ⟨0|Jz|1⟩ between the two-singlet states. As observed elsewhere for other hexagonal manganites,there is no Mn-based exchange field at the second Tm site (the 2a site) which contributes aparamagnetic subspectrum down to the lowest experimental temperature of 4.2 K.

Magnetism and transport in YbMn2Sb2

A new ternary intermetallic compound, namely, YbMn2Sb2, has been synthesized and its magnetic and electrical transport properties have been studied in the temperature range of 2–300K. This compound crystallizes in a trigonal, La2O2S-type structure (space-group P3bm1, No. 164) and is found to be ferromagnetically ordered at room temperature. The magnetism is attributed to the ordering of Mn sublattice. M5 x-ray absorption spectrum of YbMn2Sb2 obtained at room temperature suggests that the valency of Yb in this compound is close to 2+. Electrical resistivity of this compound is metal-like and a positive magnetoresistance of 13% is observed at 5K in an applied field of 9T.

Magnetization studies ofRMn6Ge6−xGaxsingle crystals (R=Sc,Y, Gd–Lu;0.63⩽x⩽1.00)

The magnetic properties of single crystals of rare-earth compounds of composition $R{\mathrm{Mn}}_{6}{\mathrm{Ge}}_{6\ensuremath{-}x}{\mathrm{Ga}}_{x}$ $(x\ensuremath{\approx}1)$ have been studied. In these compounds, the Mn sublattice orders ferromagnetically with a preferred moment direction perpendicular to the $c$ axis. In the compounds in which also the $R$ component carries a magnetic moment, the latter couple antiparallel to the Mn moments. Upon cooling from room temperature to cryogenic temperatures, the $R$-sublattice anisotropy becomes the dominant contribution to the total magnetocrystalline anisotropy, which leads to a spin-reorientation transition at intermediate temperatures for $R=\mathrm{Tb}\ensuremath{-}\mathrm{Yb}$. At low temperatures, the preferred moment directions are characterized by an easy axis for $R=\mathrm{Tb}$, Er, Tm, and Yb and by an easy cone for $R=\mathrm{Dy}$ and Ho. A satisfactory account of the observed preferred moment directions has been given in terms of crystal-field theory. Measurements of the magnetization in the main crystallographic directions have been made in high magnetic fields, up to about 55 T. The interplay between the antiferromagnetic intersublattice $R$-Mn coupling and the magnetocrystalline anisotropy leads to field-induced magnetic phase transitions which are particularly pronounced in the compounds with Ho, Er and Tm.

Magnetic ordering of the Mn sublattice: Dense Kondo-lattice behavior of Ce in(RPd3)8Mn(R=La,Ce)

We have synthesized interstitial compounds $(R{\mathrm{Pd}}_{3}{)}_{8}\mathrm{Mn}$ $(R=\mathrm{La}$ and Ce). The Mn ions in these compounds, present in ``dilute'' concentrations of just 3 molar percent, form a regular sublattice with an unusually large Mn-Mn near-neighbor distance of $\ensuremath{\sim}8.5\mathrm{\AA{}}.$ While the existence of $(R{\mathrm{Pd}}_{3}{)}_{8}M$ $(M:$ p-block element) is already documented in the literature, the present work reports on the formation of this phase with M being a $3d$ element. In $({\mathrm{LaPd}}_{3}{)}_{8}\mathrm{Mn},$ the Mn sublattice orders antiferromagnetically, as inferred from the peaks in low-field magnetization at 48 and 23 K. The latter peak progressively shifts towards lower temperatures in increasing magnetic field and disappears below 1.8 K in a field of $\ensuremath{\sim}8\mathrm{kOe}.$ On the other hand, in $({\mathrm{CePd}}_{3}{)}_{8}\mathrm{Mn}$ the Mn sublattice undergoes a ferromagnetic transition around 35 K. The Ce ions form a dense Kondo lattice and are in a paramagnetic state at least down to 1.5 K. A strongly correlated electronic ground state, arising from the Kondo effect, is inferred from the large extrapolated value of $C/T=275\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{Ce}{\mathrm{K}}^{2}$ at $T=0\mathrm{K}.$

Peculiar magnetic properties of (Dy,Ca)MnO 3

The magnetic properties of the Dy 1− x Ca x MnO 3 solid solution (0≤ x≤0.60) have been studied as a function of temperature and magnetic field. A paramagnetic state, with the Curie–Weiss temperature Θ changing from −25 to +14 K, is observed from x=0 to x=0.3. At higher calcium concentration, charge ordering effects seem to dominate. Dy–Dy interactions present in the pure DyMnO 3 manganite ( T N=9.5 K) persist in the solid solution up to x=0.3. The Mn sublattice orders ferromagnetically at T c∼80 K. The ZFC/FC magnetization cycles show a ferrimagnetic-like system, in which negatively-polarized dysprosium moments behave as free spins ( T> T N) under the internal field of the ordered Mn sublattice. The local field at a given Dy site depends on the exchange (negative) interaction between both sublattices, resulting in a reversal of the magnetization when the magnetic moment of the Dy sublattice exceeds the one of the ferromagnetic network.

Phase transitions of europium valency and manganese magnetic order and thermal hysteresis phenomena inEuMn2Si2−xGexs

The compounds EuMn{sub 2}Si{sub 2{minus}x}Ge{sub x} have been studied by {sup 151}Eu and dilute {sup 57}Fe M{umlt o}ssbauer spectroscopy, x-ray diffraction, magnetization, and resistivity measurements. In EuMn{sub 2}Ge{sub 2}, Eu is divalent and orders magnetically at 13 K. The Mn sublattice orders magnetically at T{sub c}=302 K. In EuMn{sub 2}Si{sub 2} the Eu ion is in a valence fluctuating state, at 90 K it is trivalent and at 650 K it is almost completely divalent. The Mn sublattice orders antiferromagnetically at T{sub N}=395 K, but at lower temperatures, 107, 65, and 32 K, undergoes spin reorientation transitions with a ferromagnetic component. Replacing {approximately}15{percent} of Si by Ge in EuMn{sub 2}Si{sub 2} converts all Eu ions into their divalent state. In EuMn{sub 2}Si{sub 2{minus}x}Ge{sub x}, x=0.1, 0.2, at 90 K both divalent and trivalent Eu ions are present. As the temperature is raised towards a critical temperature a first order valence phase transition occurs, all Eu{sup 3+} ions convert to Eu{sup 2+} in a short range of temperatures. This first order valence phase transition is accompanied by the antiferromagnetic phase transition of the Mn sublattice. The formation of a single first order phase transition from two interacting order parameters, each ofmore » which by itself leads to an independent second order phase transition, is predicted by theory. This phase transition has a wide thermal hysteresis loop observed by M{umlt o}ssbauer studies (both {sup 151}Eu and {sup 57}Fe), magnetization, x-ray diffraction, and resistivity measurements. For x=0.1, x=0.2 the transition temperatures are 370, 330 K with increasing temperature and 320, 275 K with decreasing temperature, respectively. {copyright} {ital 1997} {ital The American Physical Society}« less

The119Sn Mössbauer effect in RMn6Sn6 compounds (R=Gd,Y)

The magnetic properties of intermetallic compounds RMn6Sn6 (T=Gd and Y) have been investigated by119Sn Mossbauer effect measurements. The differences of the hyperfine field on both the Sn1 and Sn3 sites were small between GdMn6Sn6 and YMn6Sn6, while the Mn sublattice orders ferromagnetically for R=Gd and antiferromagnetically for R=Y. This result indicated that Mn moments order antiferromagnetically in the intra-plane of the Kagome net in YMn6Sn6.

155Gd Mössbauer effect and magnetic properties of GdMn 6Ge 6

The magnetic properties of GdMn 6Ge 6 have been studied by magnetic measurements and 155Gd Mössbauer spectroscopy. The Mn sublattice orders ferromagnetically in high magnetic fields and at high temperatures but in low fields and low temperatures there is a tendency to antiferromagnetic ordering. Antiferromagnetic order was also found in YMn 6Ge 6. The electric field gradient derived from the quadrupolar splitting of the 155Gd Mössbauer spectra is substantially larger than in the isotypic compound GdMn 6Sn 6.

Magnetism and hyperfine interactions in Eu M2Ge 2 and Gd M2Ge 2( M = Mn, Fe, Co, Ni, Cu)

X-ray, magnetic susceptibility and 151Eu, 155Gd Mössbauer effect studies of Eu M 2Ge 2 and Gd M 2Ge 2 were performed. All compounds crystallize in the ThCr 2Si 2 body centered tetragonal structure. In all compounds, except those with M = Mn and in Eu M 2Ge 2, the M component carries no magnetic moment. All compounds except those with Mn are antiferromagnetic at low temperatures. In EuMn 2Ge 2 the Mn moments order ferromagnetically at 330 K and change to antiferromagnetic order when the Eu moments order ferromagnetically (9 K). This behaviour is different from that in GdMn 2Ge 2, where the Mn sublattice orders antiferromagnetically at 365 K and becomes ferromagnetic and antiparallel to the ferromagnetic Gd sublattice at 96 K. The Mössbauer studies of 151Eu and 151Gd provide values for the magnetic hyperfine fields, the quadrupole interactions and the orientation of the magnetic moments relative to the local fourfold axis ( c-axis). It turns out that in the Eu compounds the easy axis of magnetization is close to the c-axis, while in the Gd compounds it is in the basal plane. In all systems, excluding those with Mn, the interatomic rare earth-rare earth distances have the dominant effect on the conduction electron charge density and polarization at the rare earth site and on the Curie point.