Sublattice Anisotropy Research Articles

The Gd anisotropy in GdCo 5

High-field magnetization curves of single-crystalline GdCo 5 have been measured at 4.2 K up to 35 T in order to clarify the presence of an extra Gd contribution to the magnetocrystalline anisotropy. The 3d-4f exchange interactions and the Co sublattice anisotropy have been evaluated in GdCo 5 and Gd 2Fe 17. No significant Gd contribution to the anisotropy has been revealed.

Magnetic study of SmCo5, PrCo5, SmCo4B, and Sm3Co11B4 under pulse high field

Magnetization curves and hysteresis loops for field-oriented powders of Smn+1Co3n+5B2n (n=0, 1, and 3) and PrCo5 were measured at T=4.2 K and partly at 77 K, under a strong pulsed field up to 36 T. Magnetic measurements for Smn+1Co3n+1B2n (n=1, 2, and 3) compounds were also performed. Huge anisotropy fields of 120 T for SmCo4B and of 130 T for Sm2Co7B3 were obtained. The Sm sublattice anisotropy of SmCo4B was found to be larger than that of SmCo5. To explain this, the Sm f-electron state for n≥ (R18)2 of Smn+1Co3n+5B2n has been expected to change from that for n≤1. Huge coercivities of 8 T and 27.5 T were observed at T=4.2 K for SmCo4B and for Sm2Co7B3 respectively. Magnetization processes for field-oriented PrCo5 at T=4.2 K were found to be similar to those of Nd2Fe14B at T=4.2 K.

Magnetic properties of RTiCo11 compounds with the ThMn12 structure

Magnetic properties of RTiCo11 (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) compounds with the ThMn12 structure were investigated in the temperature range from 4.2 to 1400 K. The Curie temperatures of this series exceed 1000 K and the Co atomic moments were found to take the values ranging from 0.99 to 1.80 μB, which depend on R. The easy magnetization direction of RTiCo11 was found to be axial(c∥) for R except being planar for R=Sm and Er. This result suggests that the R sublattice with a positive Stevens factor demonstrates planar anisotropy. The Co sublattice anisotropy constant was estimated to be K1 = 7.5 × 106 erg/cc at room temperature from measurements on YTiCo11. By subtracting K1 of YTiCo11 from K1 of DyTiCo11, the anisotropy constant of the Dy sublattice was obtained to be 5.7×106 erg/cc. Spin reorientation was also observed in RTiCo11 with R=Pr, Nd and Dy, which are considered to be an axial to planar one with increasing temperature.

Structural and magnetic properties of the rare-earth iron nitride solution series Y 2(Fe 1− xCo x) 17N 3−δ

Interstitial ternary nitrides Y 2(Fe 1− x Co x ) 17N 3−δ have structures related to the hexagonal Th 2Ni 17 structures of the parent Y 2(Fe 1− x Co x ) 17 compounds. Nitrogen uptake varies with cobalt concentration from δ = 0.4 at the iron rich end ( x = 0) t o δ = 1.4 with increasing cobalt concentration. Unit cell volumes are typically 5% greater in the nitrides. The 3d sublattice anisotropy is modified upon nitrogenation, the transition from easy plane to easy axis shifting from x ≈ 0.5 in Y 2(Fe 1− x Co x ) 17 to x ≈ 0.15 in Y 2(Fe 1− x Co x ) 17N 3−δ. The room temperature saturation magnetisation is greatest when x ≈ 0. 2 with a value of 170(4) J/(T/K g). Increasing the cobalt content raises the process temperature required to produce the Y 2(Fe 1− x Co x ) 17N 3 −δ phase. For x ≥ 0.85 the nitrogen absorption temperature is higher than the disproportion temperature of the Y 2(Fe 1− x Co x ) 17N 3−δ phase, thus no 2:17: N phase is observed in the range 0.85 < x < 1.0. Y 2(Fe 1− x Co x ) 17N 3−δ phase, thus no 2:17:N phase is observed in the range 0.85 < x < 1.0.

Magnetic properties of R 2Fe 17N 2.7 compounds

We have studied the magnetic properties and decomposition behaviour of various ternary nitrides of the type R 2Fe 17N 2.7 with R ≡ Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. The magnetic anisotropy of the R 2Fe 17N 2.7 compounds was studied on magnetically aligned powders in field strengths up to 35 T. The rare-earth sublattice anisotropy is much stronger in R 2Fe 17N 2.7 than in R 2Fe 17, leading to an easy c-axis anisotropy in Sm 2Fe 17N 2.7. For Er 2Fe 17N 2.7 and Tm 2Fe 17N 2.7 spin-reorientation transitions were observed upon cooling from room temperature, starting at about 150 and 225 K, respectively. The intersublattice-coupling strength between the R- and Fe-sublattice magnetization was found to remain approximately unaltered after charging R 2Fe 17 with nitrogen gas.

Phase analysis and magnetic properties of RTiFe11−xCox (R=Y,Gd) (x=0–11)

Both as-cast and 1000 °C annealed RTiFe11 samples are nearly single phase with a small amount of Fe2Ti. Small amounts of Co additions do not change the microstructure, but the minor phase changed to a Fe,Co,Ti solid solution. At high Co concentration, as-cast samples are multiphase [1-12, 2-17, (Fe,Co,Ti)] and high-temperature (∼1200 °C) annealing is needed in order to produce a single-phase microstructure. Results of x-ray analysis and magnetic measurements show that YTiFe11, YTiCo11, GdTiFe11, and GdTiCo11 are uniaxial and their anisotropy fields at room temperature are 22, 18, 33, and 25 kOe, respectively. Therefore, Fe and Co sublattices are uniaxial with Fe sublattice anisotropy stronger than that of Co. In the intermediate range of composition, there is a conical-planar region for both Y and Gd systems and spin reorientations with temperature were observed. In general, the anisotropy behavior of the RTiFe11−xCox systems (R=Y,Gd) is similar but opposite to their counterpart of R2Fe17−xCox. This is due to the similarity of their crystal structure, as both are derivatives of 1-5. However, the strong contribution from the K2 anisotropy constant makes the anisotropy phase diagrams of 1-12 more complicated than those of 2-17.

Anisotropy field measurement in barium ferrite powders by applied field Mossbauer spectroscopy

A new method for measuring magnetic anisotropy in ferrimagnetic powders using applied field Mossbauer spectroscopy has been developed. The method is based on using a uniaxial anisotropy mean-field model to calculate the equilibrium spin orientations as a function of applied field and compute the corresponding Mossbauer spectra. A variety of asymmetric broad line profiles are predicted which are sensitively dependent on the magnetization and the exchange and anisotropy terms. In principle the technique enables the determination of individual sublattice anisotropies, although in the case of pure and Co-Ti substituted barium ferrite the sublattice anisotropies are found to be experimentally indistinguishable. A mean anisotropy is obtained which compares favourably with the results of other measurements on barium ferrite.

Competing anisotropies and first-order magnetization processes

The analysis of the canting model theory up to the fourth order, including the in-plane contribution to the total anisotropy, is presented. The origin of the first-order magnetization process (FOMP) is well explained in terms of competing anisotropies. The fourth-order terms are essential for the presence of a FOMP; in fact, computer simulations, with only second-order terms, show regular magnetization curves, and the representation, in terms of equivalent single sublattice anisotropy constant K*i, explains the origin, from the competition, of the high-order terms, but they are not strong enough to produce FOMP transitions. An analysis of the effects of each parameter in the energy expression is given, in particular the behavior of the magnetization curves and the evolution of the easy cone are studied. An analytical expression for the anisotropy field and of the energy instability at zero field (origin of easy cone) has been derived. As an application of the model, an analysis of the magnetization curves, in hard direction of single crystals of PrCo5, Nd2Fe14B, and Pr2Fe14B is given; the good agreement with experimental results shows that the above model explains well the origin of the spin reorientation and of the FOMP transitions observed in these compounds.

Crystal fields and exchange interactions in Yb2Fe17: A 174Yb Mössbauer study (abstract)

Most rare-earth -(R) iron compounds R2Fe17 crystallize in the hexagonal Th2Ni17 structure with two inequivalent rare-earth sites in the unit cell. For Tm2Fe17 magnetic anisotropy of opposite character has been determined for the two Tm sites.1 Nevertheless, the axial anisotropy of one Tm site dominates at low temperatures and forces the magnetic moments to the direction parallel to the c axis below the spin-reorientation temperature TSR=74 K. Magnetization measurements on Yb2Fe17 gave no indication for a spin reorientation.2 In this compound, the Fe sublattice anisotropy seems to dominate at all temperatures, confining the moments to the plane perpendicular to the c axis. This has now been confirmed by 174Yb Mössbauer spectra of Yb2Fe17 in the temperature range 1.6–100 K. The different crystal fields acting on the Yb 4f shell at the two sites lead to a large difference in the static moments as revealed by the different hyperfine fields. From the temperature dependence of the magnetic and electric hyperfine interactions, values for the crystal-field parameters and exchange fields at both Yb sites have been derived. Structural disorder, probably due to random occupation of Yb sites by Fe2 dumbbells, leads to distributions of the crystal-field parameters and to considerable broadening of the Mössbauer spectra.

Magnetic and crystallographic characteristics of rare-earth ternary carbides derived from R 2Fe 17 compounds

We have studied the magnetic properties of the rhombohedral R 2Fe 17C compounds with R = Ce, Pr, Sm, Gd, Tb, Dy, Ho or Y and the hexagonal R 2Fe 17C compounds with R = Er, Tm or Lu. For all compounds the lattice parameters were determined. The Curie temperatures were found to be considerably enhanced with respect to the C-free counterparts. The magnetic anisotropy of the R 2Fe 17C compounds was studied on magnetically aligned powders in field strengths up to 35 T. The rare-earth sublattice anisotropy is much stronger in R 2Fe 17C than in R 2Fe 17, leading to an easy c-axis anisotropy in Sm 2Fe 17C even at room temperature. The Curie temperatures and the high field data obtained at 4.2 K were analysed in terms of a mean field model.

ST RUCTURAL AND MAGNETIC PROPERTIES OF TERNARY NEODYMIUM-IRON-CARBON (OR CARBON-BORON) COMPOUNDS

Crystallographic and magnetic properties of the Nd14Fe78B8-xCx compounds were investigated. The properly annealing treatment was found to be the condition that the compounds of light rare earth-iron-carbon belonging to the P42/mnm type structure could be formed. The magnetic ordering temperatures of the compounds decreased somewhat with increasing the carbon concentration, but the saturation magnetization σs had a gentle maximum, and the residual ma gnetization σr, intrinsic coercivity iHe as well as the anisotropy field Ha at room temperature showed a significant increase. The anisotropy behaviours of the C-containing samples were similar to Nd-Fe-B. The fact that the transition temperatures of spin reorientation gradually descended with increasing the carbon content while the canting angle at 1.5 K had a slight increase suggested that there was complicate coupling between the anisotropies of Nd and Fe sublattices. In addition, the suitably Nd-rich carbide exhibited relatively large anisotropy.

Structure and magnetic properties of R2Fe14B1-xCx compounds (R=Y,Nd)

Magnetization curves parallel and perpendicular to aligned direction were measured in an extraction magnetometer (magnetic field up to 80 kOe) on R2Fe14 B0.5 C0.5 compounds (R = Y,Nd) from 1.5 to 300 K. Modified Sucksmith-Thompson method was used to determine anisotropy constants K1 and K2. It was found that the mean Fe moment, Curie temperature and spin reorientation temperature of the Nd-containing compound were decreased upon substitution of carbon for boron, however, the anisotropy field Ha was increased with such substitution. X-ray diffraction analysis showed that values of (1 - α(c/a)2) of the compound in which boron was partially substituted by carbon was larger than that of the unsubstituted one. It is thought that the crystal field acting on the Fe sublattice is increased with carbon substitution. The decrease of Tsr of Nd2Fe14B0.5C0.5 compared with that of Nd2Fe14B is probably due to the increase of the Fe sublattice anisotropy. The value of Ha determined by the SPD method differs significantly from that derived by 2(K1 + 2K2)/Ms. It seems that the anisotropy constants K1, K2 determined by the Sucksmith-Thompson method does not completely represent the anisotropy behaviour of this type of compound. The nominal R2Fe14C samples are a mixture of two phases (R2Fe17Cx + α − Fe) and the Nd2Fe14B type compound was not found in this case. The fact that R2Fe17Cx has a higher Curie temperature compared to that of R2Fe17 is worth noticing.

AC susceptibility measurements in some RTiFe 11-xCo x (R = Dy, Ho, Er) compounds: Spin-reorientation behavior

The DyTiFe 11 - x Co x ( x = 0, 1, 3), HoTiFe 11 - x Co x ( x = 0, 3) and ErTiFe 11 compounds, all exhibiting the T hMn 12-type structure, were studied for their ac susceptibility in the temperature range 20–300 K. The Dy- and Ho-containing compounds exhibited spin reorientation from axial to cone to planar, or from axial to cone in the temperature range 250-50 K, as expected. In this structure Dy and Ho with negative second-order Stevens' coefficients (α J < 0) favor planar rare earth sublattice anisotropy, while Fe and Co sublattices favor uniaxial and planar anisotropies, respectively and would be in competition as a function of temperature. A spin-reorientation type of behavior was also observed in the ErTiFe 11 compound near 50 K. This observation appears to imply that, in this compound, the higher-order crystal-field terms are important. The magnetization data revealed that in these systems the rare earth and transition metal sublattices coupled antiparallel, as is normally the case in the heavy rare-earth-transition-metal compounds.

Magnetic properties of the ternary carbides Tm 2Fe 17C x

We have investigated the crystallographic and magnetic properties of the ternary carbides Tm 2Fe 17C x by means of X-ray diffraction, 57Fe Mössbauer spectroscopy, 169Tm Mössbauer spectroscopy and magnetic measurements. It is shown that small amounts of carbon raise the Curie temperature in Tm 2Fe 17C x from below room temperature to about 500 K, at the same time increasing the average Fe moment. Important conclusions regarding the rare-earth sublattice anisotropy were derived from the quadrupole splitting of the 169Tm Mössbauer spectra and from the strong concentration dependence of the spin reorientation temperature in Tm 2Fe 17C x .

Intrinsic magnetic properties of the iron-rich ThMn12-structure alloys R(Fe11Ti); R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu

Magnetic properties of the series of ThMn12-structure intermetallic compounds R(Fe11Ti) have been determined for rare earths from Nd to Lu plus Y. The highest Curie temperature (607 K) is for R=Gd, and R-Fe exchange interactions are much stronger for light rare earths than for heavy ones. The temperature dependence of the iron sublattice magnetisation and anisotropy are determined for the Y and Lu compounds. Spin reorientation transitions are found as a function of temperature for the rare earths with a negative second-order Stevens coefficient alpha J(Nd, Tb, Dy), and a set of crystal-field parameters is derived to account for the transitions in a consistent way. A sharp increase in magnetisation observed for Sm(Fe11Ti) below 130 K in a field of about 10 T applied perpendicular to the easy direction indicates that J-mixing may be important for Sm3+. Compared with R2Fe14B, the iron anisotropy in R(Fe11Ti) is greater, and the rare-earth anisotropy is much weaker at low temperature, with the opposite sign for the rare-earth crystal-field coefficient A20. The average iron moment is 1.7 mu B in R(Fe11Ti) at 4.2 K; Mossbauer spectra are analysed to yield the average moments on each site. Limits set by the intrinsic magnetic properties on the performance of magnets made from these families of alloys are discussed.

Moment reduction in RFe 12- xT x compounds (R=Gd, Y and T=Ti, Cr, V, Mo, W)

We have investigated the magnetic properties of several ternary compounds of the type RFe 12- x T x , where R represents Y or Gd and T=Ti, Cr, V, Mo, W. For all compounds investigated we have determined the saturation magnetization at 4.2 K, the latter being derived from magnetic isotherms measured in fields up to 21 T. It is shown that the Fe moment in these materials varies with the T component in a manner which can qualitatively be understood on the basis of Friedel's model. We also found that the Fe sublattice anisotropy is strong in all these compounds (in the Y compounds the anisotropy field B A≈5T and in the Gd compounds B A≈7 T), except for the compounds based on Mo.

ChemInform Abstract: Effects of Hydrogen Absorption on the 3d and 4f Anisotropies in RE2Fe14B (Re: Y, Nd, Ho, Tm)

Abstractare investigated using the singular point detection technique in the temp. range 77‐293.

Effects of hydrogen absorption on the 3d and 4f anisotropies in RE2Fe14B (RE ≡ Y, Nd, Ho, Tm)

Abstract The effects of hydrogen absorption on the iron and rare earth sublattice anisotropies in RE2Fe14B (RE ≡ Y, Nd, Ho, Tm) have been investigated using the singular point detection technique. Hydrogen is found to substantially depress both the iron and rare earth contributions to the magnetocrystalline anisotropy. However, such a reduction appears to be very large for holmium, and particularly for neodymium, which both give a resultant axial anisotropy. It is less important in the case of thulium which gives a resultant planar anisotropy. The observed hydrogen composition dependence of the holmium anisotropy implies the existence of a particular hydrogen filling sequence.

Magnetic anisotropy energy in single crystal Y1.8Er0.2Fe14B (invited) (abstract)

There has been considerable interest in tetragonal R2Fe14B compounds as a basis for a new class of permanent magnet materials because of the unusually large energy products they exhibit at room temperature for certain rare-earth substitutions. The origin of the high-energy products is directly related to the large saturation magnetization and magnetic anisotropy energy. The magnetocrystalline anisotropy energy is believed to be directly related to an interaction between the 4f-electrons and the crystal field: however, to date few if any direct comparisons have been made between the experimental magnetic anisotropy and crystal field theory. The reason being that the large anisotropy energy makes it very difficult to use conventional torque magnetometry techniques to determine the angular dependence of the magnetic free energy, particularly at low temperatures where the higher-order terms become important. In this investigation we determine the angular dependence of the magnetic free energy as a function of temperature for Y1.8Er0.2Fe14B using high field (6 T) torque magnetometry techniques and make a direct comparison of the free energy with the energy calculated using a model based on crystal field theory. Y1.8Er0.2Fe14B was chosen because the Fe and Er sublattice anisotropy energies nearly cancel at low temperatures making it possible to measure anisotropy. Excellent agreement was obtained between the model and experiment.

Spin reorientation in (RE)2 (TM)14B alloys (RE = rare earth, TM = transition metal)

Spin reorientation in (RE)2 (TM)14B alloys has been studied by Moessbauer spectroscopy of oriented and powder samples. The competition of the CEF anisotropy for two rare earth elements with opposite Stevens factors has been investigated in the system Er2-xDyxFe14B. The competition between the rare earth and transition metal sublattice anisotropy has been examined in the system Nd2Co14B doped with 1% Fe57 and it has been found that spin reorientation occurs at 550±2K.