3d Sublattice Research Articles

Influence of Mn substitution on the magnetic properties of Ho2Fe14C compounds

The crystallographic and magnetic properties of the compounds Ho2Fe14−xMnxC have been investigated by means of x-ray diffraction and magnetic measurements. Magnetization measurements made in fields up to 38 T showed that the saturation moment exhibits a minimum at a Mn concentration corresponding to about x=2. The occurrence of this minimum is explained by antiparallel coupling between the Ho and 3d sublattice magnetization, the latter becoming strongly reduced with increasing Mn concentration. Most of the Ho2Fe14−xMnxC compounds investigated have a break in the magnetization curves measured at 4.2 K. This break is interpreted as the onset of decoupling between the antiparallel coupling between the rare-earth and 3d sublattice. A mean-field analysis was used to derive the intersublattice molecular-field coefficients nRT.

Magnetic properties of Er2Fe14−xMnxC

The magnetic properties of the compounds Er2Fe14−xMnx have been determined by means of X-ray diffraction, magnetic measurement and 57Fe Mössbauer spectroscopy. Magnetization measurements made in fields up to 38 T showed that the saturation moment exhibits a minimum at a Mn concentration corresponding to about x=2, due to the antiparallel coupling between the R and 3d sublattice magnetizations the latter becoming strongly reduced with increasing Mn concentration. The reduction of the 3d-sublattice magnetization is accompnied by a corresponding reduction in the 57FE hyperfine fields and by a lowering of the Curie temperature and the spin orientation temperature. Most of the compounds investigated have a break in the magnetization curves measured at 4.2 K which is interpreted as the onset of decoupling between the antiparallel rare earth and 3d sublattices. A mean field analysis was used to derive the intersublattice molecular field coefficient nRT.

Magnetic properties of the 3d sublattice in pseudoternary compounds Y2Fe14-xMxB with M = Co and Mn

The magnetic properties of Y2Fe14-xCoxB (0 ⩽ x ⩽ 12) and Y2Fe14-xMnxB (0 ⩽ x ⩽ 5) have been investigated by 57Fe Mössbauer spectroscopy. Single crystalline samples of Y2Fe14-xCoxB were used in magnetization measurements. The magnetic hyperfine field of Fe in Y2(Fe, Co)14B decreases monotonically with increasing Co content, and the value obtained are not entirely coincident with those estimated from the magnetization. The results are discussed in connection with the rigid band model and the magneto-volume effect. Mn substitution considerably reduced both of the magnetization and the Curie temperature. It was found that the Mn atom has no magnetic moment and take no part in magnetic interaction.

Magnetic and anisotropy properties of the Y 2Fe 17−xMn x and Er 2Fe 17−xMn x compounds

The effects of Mn-substitutions in the Y 2Fe 17 and Er 2Fe 17 compounds have been studied by magnetization measurements. The magnetic moment and the magnetic anisotropy of the 3d sublattice are found to reduce upon increasing the Mn-concentration. The magnetization reorientation processes that exist in the Er 2Fe 14Mn 3 and Er 2Fe 13Mn 4 compounds are, therefore, a consequence of competing contributions of the planar anisotropy of the 3d sublattice and the axial one of the erbium partner.

Magnetic anisotropy in the system La 2Fe 14 − xCo xB and its relation to the system Nd 2Fe 14 − xCo xB

We have studied the system La 2Fe 14 − x Co x B by means of X-ray diffraction, magnetic measurements and singular point detection (SPD) measurements. We present experimental data on the concentration dependence of the lattice constants, Curie temperatures, saturation magnetization and anisotropy fields. Attention is mainly given to the determination of anisotropy fields, which were also studied as a function of temperature in the range from 4.2 K to the corresponding Curie temperatures. The experimental information obtained for the system La 2Fe 14 − x Co x B was used to distinguish the relative anisotropy contributions of the neodymium sublattice and 3d sublattice in Nd 2Fe 14 − x Co x B.

Magnetism of the Tb 2Fe 14−xCo xB system

The Tb 2Fe 14− x Co x B materials were synthesized for the entire composition range ( x = 0–14) and studied by X-ray and magnetometry methods. All materials have a tetragonal crystal structure with decreasing lattice parameters upon Co substitution. The Curie temperature markedly rises for alloys with low Co content. Saturation magnetization at 77 K reaches a slight maximum around x ≈ 1 and gradually decreases for higher Co concentrations. An antiparallel coupling of 3d and Tb magnetic moments is inferred from saturation magnetization data. Anisotropy fields exhibit a maximum at low Co contents, but they decrease rapidly for x > 5. A spin reorientation (axis-to-plane) occurs at high temperature in materials with x ⩾ 12.5 due to competing effects of the terbium sublattice anisotropy and the 3d sublattice anisotropy. The spin-reorientation temperature becomes lower for alloys with higher Co content. The observed magnetic behavior is discussed in terms of preferential Co substitution into 16 k 2 sites and changes in the 3d sublattice due to Co introduction. A magnetic phase diagram is constructed for the Tb 2Fe 14- x Co x B system and compared with that of Pr 2Fe 14- x Co x B and Nd 2Fe 14 - x Co x B systems.

Magnetism of R2Co14−xSixB systems (R=Y, Pr, and Nd)

The R2Co14−xSixB systems (R=Y, Pr, and Nd) have been synthesized for x ranging from 0.0 to 3.0 and found to have the tetragonal crystal structure for x≤2 in Pr- and Nd-based systems and for x≤1.6 in Y-based systems. Bulk magnetization measurements have been carried out in the temperature range 4.2–1100 K to determine the saturation magnetizations, anisotropy fields, Curie temperatures, TC, and spin-reorientation temperatures for different Si contents. A decrease of the TC and the saturation magnetization was observed with increasing Si content. The anisotropy field in Pr- and Nd-based systems was found to increase at 77 K and decrease at 295 K. The high-temperature spin reorientations for Nd- and Pr-based systems disappear for x≥1.3 and 1.0, respectively. The low-temperature spin reorientation observed in Nd2Co14B also vanishes for x>0.3. The observed features are discussed in terms of weakening the 3d sublattice magnetization and its anisotropy due to Si dilution.

Kerr effect in R 2Fe 14B and R 2Co 14B compounds

The polar Kerr effect in several compounds of the R 2Fe 14B and R 2Co 14B series (R=rare earth metal) at room temperature was measured in the energy range 0.5–5 eV. It was found that the 3d sublattice magnetization is mainly responsible for the Kerr effect. The potential use of R 2Fe 14B compounds for erasable magneto-optical recording is briefly discussed.

Magnetic Anisotropy and Spin Reorientation in Nd2-xPrxCo14B

ABSTRACTNd2-xPrxCo14B intermetallics crystallize in tetragonal form isostructural to Nd2Fe14B. Structural and magnetic properties of the polycrystalline materials have been determined. Room temperature magnetic measurements indicate that these intermetallics exhibit uniaxial anisotropy throughout the entire composition range. Substitution of praseodymium in Nd2-xPrxCo14B significantly enhances the anisotropy field both at 78 K and at room temperature. Magnetization versus temperature plots show spin reorientation TSR2 at 546 K for Nd2Co14B and at 668 K for Pr2Co14B. TSR2 increases linearly with composition x. The 3d sublattice anisotropy which seeks the tetragonal plane appears to dominate above these temperatures. In addition to the above, low temperature magnetic measurements demonstrate the spin reorientation in Nd2Co14B and Nd1.9Pr0.1Co14B. Further additions of praseodymium strengthen the axial anisotropy at temperatures down to 4.2 K. Effect of competing crystal field interactions and the consequences of praseodymium substitution that result in considerable increase in anisotropy field in these quaternaries are discussed.

Structure and magnetism of the Pr 2Fe 14- xCo xB system

Isostructural, tetragonal materials were synthesized for the entire composition range ( x = 0 to 14). They were studied by X-ray and magnetometry methods. Magnetization measurements confirm a ferromagnetic arrangement of 3d and Pr magnetic moments and reveal a sharp increase of the Curie temperature with the increase of Co concentration. Saturation magnetization at 295 and 77 K reaches a slight maximum around x = 1 and gradually decreases for higher Co content. Anisotropy fields initially decrease and afterwards increase very quickly as more Co is introduced to the system. A spin reorientation occurs in alloys with x ⩾ 9.5 at temperature higher than 660 K. It marks a transition between uniaxial anisotropy and planar anisotropy. Spin reorientation temperature becomes lower for materials with higher Co content. A discussion of the Curie temperature change is conducted in terms of preferential substitution of Co into 16k 2 sites. The weakening of the exchange interaction between Pr and 3d sublattices, as well as the decreasing Pr-sublattice anisotropy with rising temperature, are considered to be responsible for anisotropy field changes. The interplay between crystal field and exchange field interactions is emphasized. A comparison with the Nd 2Fe 14- x Co x B system is included.

Magnetic phase transitions and magnetic anisotropy in Nd 2Fe 14 − xCo xB compounds

The temperature dependence of the anisotropy field of Nd 2Fe 14 − x -Co x B has been measured between 77 K and the Curie temperature, using the singular point detection (SPD) technique. The anisotropy field at room temperature is found to decrease with increasing cobalt content. Measurements of the temperature dependence of the initial susceptibility show that at a temperature T 1, which is below room temperature, the easy magnetization direction changes. The origin of the change is attributed to the neodymium-sublattice anisotropy. For the cobalt-rich samples ( x ⩾ 5) it is found that at temperatures T 2 higher than ambient temperatures a second spin reorientation takes place, which is attributed to the competing effect of the neodymium sublattice anisotropy and the 3d sublattice anisotropy.

Ordering of atoms in 3d sublattice of the intermetallic quasibinary system Dy(Fe1?xMnx)2

Methods of x-ray analysis and nuclear γ-resonance (Mossbauer effect) have been used to study the distribution of iron and manganese atoms in the intermetallic quasibinary system Dy(Fe1−xMnx)2, which is isostructural to the Laves phase C15. Ordering of atoms of transition metals has been found in 3d sublattice of intermetallic compounds Dy(Fe1−xMnx)2 with the formation of a triple superstructure having the stoichiometric composition Dy(Fe0·.25Mn0·.75)2.

Magnetic and crystallographic properties of ternary rare earth compounds of the type R 2Co 14B

Compounds of the type R 2Co 14B having the tetragonal Nd 2Fe 14B structure were found to exist for R = Y, La, Pr, Nd, Sm, Gd and Tb. The lattice constants of all these compounds were determined. Differential scanning calorimetry was used to determine the Curie temperatures of these materials, ranging from T c=955 K for La 2Co 14B to T c = 1050 K for Gd 2Co 14B. The saturation moment and anisotropy fields were studied at 4.2 K on magnetically aligned powder samples in magnetic fields up to 35 T. Estimated values of the anisotropy fields range from 6 T for La 2Co 14B to 75 T for Pr 2Co 14 B. The 3d sublattice anisotropy favours an easy magnetization direction perpendicular to the c axis whereas the crystal field induced anisotropy of the 4f sublattice corresponds to the second-order Stevens factor α J of the R component. As in R 2Fe 14B, the 3d sublattice moment couples antiparallel with the spin moment of the 4f sublattice.

Magnetovolume effect in intermetallic compounds Dy 2(Fe-M) 17: M = Al and Co

The dependence of the spontaneous magnetostriction on temperature and Al, Co concentration was estimated from the thermal expansion measurements. For Dy 2Fe 17 the spontaneous magnetostriction is 1.62%, being nearly as large as in the Fe-Ni Invar alloys. Although Dy atoms themselves have their own large magnetic moments, the linear correlation between the spontaneous magnetostriction and the square of the 3d sublattice magnetisation, being a function of temperature and Al and Co concentration, was found. Plots of λ m vs M 2 3d are linear but do not cross the zero point. The magnetovolume coupling constant κC int = 0.8 × 10 −7 m 3J −1 = 4 × 10 −3 μ 2 B for Dy 2Fe 17 is similar to that in the other Fe compounds. The magnetic Grüneisen parameter γ m = -5.8 was estimated.

Mössbauer effect study of Tm2Fe17− xCox and related compounds

Mössbauer spectra (4–700 K) of Tm 2 Fe 17− x Co x and of several R 2Fe 17 compounds were obtained. The easy magnetization direction is discussed in terms of a crystal field induced R sublattice anisotropy, competing with the 3d sublattice anisotropy. In the pseudobinaries Fe shows a preference to occupy the dumb-bell shaped f sites.

Magnetic interactions in pseudobinary rare earth-3d intermetallics

Magnetic measurements on pseudobinary intermetallic compounds of the series R(Mn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (R = Y, Gd, Er) R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> (Mn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</inf> (R = Y, Gd, Tb, Dy, Ho, Er, Tm) R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> (R = Y, Gd, Dy) R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> (R = Y, Gd) are reported. Magnetization and susceptibility measurements have been performed at temperatures from 4 K to 1500 K. The magnetic interactions between Mn and Fe are discussed in terms of a localized-moment model. In the case of the R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> (M = Co, Ni) compounds, a band model seems to be more appropriate. Mössbauer Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sup> spectra obtained on the R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe,Co) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> series can be explained by a superposition of four different six-line patterns corresponding to the four crystallographically nonequivalent 3d sublattices.