X.C. Kou

Magnetic anisotropy and spin-reorientation transitions in RFe11Ti (R = Nd, Tb, Dy, Er) rare-earth intermetallics

Abstract RFe 11 Ti rare-earth intermetallics (R = Nd, Tb, Dy, Er) which show temperature-induced spin-reorientation transitions (SRT) were investigated. The temperature dependences of the rare-earth anisotropy constants were calculated using the single-ion model. By fitting the experimental data a set of crystal-field and exchange-field parameters for R 3+ ions wassb deduced. The temperature dependence of the first-order magnetization process fields was calculated for NdFe 11 Ti and ErFe 11 Ti within the model. The calculated spin-reorientation transition in NdFe 11 Ti observed at T s = 189 K is of first order with a discontinuous jump of the magnetization angle. Present calculations show that a first-order transition occurs in DyFe 11 Ti at low temperatures. A second-order SRT from ‘easy axis’ to ‘easy cone’ exists in ErFe 11 Ti. A first-order SRT ‘easy axis’-‘easy plane’ is predicted theoretically in TbFe 11 Ti. The calculated curves of the temperature dependence of the anisotropy fields and the critical fields of the first-order magnetization processes for RFe 11 Ti using the fitted crystal- and exchange-field parameters are in good agreement with the experimental data over a wide temperature range.

Magnetocrystalline anisotropy of non-uniaxial R - T magnetic materials studied by the singular point detection technique: an application to compounds (R = Y or Gd and x = 0 or 1)

The easy magnetization direction of lies within the basal plane over all magnetic ordering temperatures. A spinning-sample magnetic alignment technique was used to align the basal planes of fine single crystallites of (R = Y or Gd and x = 0 or 1) to be parallel to each other. The degree of magnetic alignment was checked by x-ray diffraction. The magnetocrystalline anisotropy field of has been determined by a singularity appearing in the curve of versus H measured on a magnetically aligned sample when an external field is applied perpendicular to aligned basal planes. The temperature dependence of the anisotropy fields was measured from 4.2 K up to the corresponding Curie temperatures. It was found that the Curie temperatures of compounds with R = Y or Gd were enhanced upon partial substitution of Fe by Ga. However, the magnetic anisotropy fields of Ga-containing compounds are smaller than those of the corresponding pure compounds at low temperatures.

Structural and intrinsic magnetic properties of (Sm1−xNdx)2Fe17N≈2.7 and Sm1−xNdx)2(Fe1−zCoz)17N≈ 2.7

Abstract Formation and magnetic properties of interstitital (Sm 1−x Nd x ) 2 Fe 17 N ≈2.7 nitrides are reported. The thermal stability of Sm 2 Fe 17 N ≈2.7 is not much affected by substituting Nd for Sm, whereas the Curie temperature is slightly decreased from 746 K for x = 0 to 725 K for Nd 2 Fe 17 N ≈2.7 . The saturation polarization increases from 1.52 T for x = 0 to 1.60 T for x = 1. The strong uniaxial anisotropy of Sm 2 Fe 17 N 2.9 ) H A = 21.0 T at room temperature) is significantly reduced by substituting Nd for Sm due to the strong planar anisotropy of Nd 2 Fe 17 N ≈2.7 ( K 1 = −6.8 MJ/m 3 and K 2 = 0.8 MJ/m 3 ). For intermediate Nd contents the easy magnetization direction changes from the c -axis over an easy cone to the basal plane with decreasing temperature. By substituting Co for Fe the decrease of the anisotropy field can be partly balanced and the saturation polarization and the Curie temperature are further increased, giving H A = 14.8 T, J s = 1.57 T and T C = 835 K for (Sm 0.7 Nd 0.3 ) 2 (Fe 0.8 Co 0.2 ) 17 N ≈2.7 .

Studies on Nd(Fe/sub 0.92-x/B/sub 0.08/Ga/sub x/)/sub 5.5/ sintered permanent magnets

The temperature dependence of the hysteresis loop and the anisotropy field H/sub A/ of sintered magnets of the composition Nd(Fe/sub 0.92-x/B/sub 0.08/Ga/sub x/)/sub 5.5/ was investigated using pulsed-field equipment. Analysis based on the nucleation model was performed. The spin reorientation temperatures were determined by measurements of the temperature dependence of the initial AC susceptibility chi /sub ac/(T). It is shown that chi /sub ac/(T) curves can be used to determine the temperature where the FOMP (first-order magnetization process) transition starts. >

Magnetic phase transition and magnetocrystalline anisotropy of Sm2Fe17CxNy

Alternating current (ac) susceptibility and high magnetic field measurements were performed to investigate the magnetic phase transitions and the magnetic anisotropy fields in Sm2Fe17CxNy with x=0, 0.4, 0.7, and 0.9. An unidentified magnetic phase transition is observed in all Sm2Fe17CxNy compounds, which is neither due to a spin reorientation nor due to a first‐order magnetization process (FOMP) transition. Samples of Sm2Fe17CxNy (x≳0) have even higher anisotropy fields than are found in Sm2Fe17Ny.

Magnetocrystalline anisotropy of Er2Fe14B

Abstract A rotation-magnetic-alignment method was used to align fine-powdered ( μ m) Er 2 Fe 14 B at room temperature while the easy magnetization direction of Er 2 Fe 14 B lies in the basal plane. X-ray diffraction was used to check the magnetic alignment. For the first time, the temperature dependence of the anisotropy field of Er 2 Fe 14 B was measured in a wide temperature range from about 170 to 530 K. The anisotropy field was determined using the SPD technique in a pulsed-field magnetometer from 170 to 320 K ( T SI = 323 K) on a magnetically aligned sample and from 330 to 530 K ( T C = 550 K) on a bulk polycrystal.

A comparison of the magnetic anisotropy of R2Fe14B with R2Fe14C compounds (R= Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu)

Abstract The magnetic properties of the R 2 Fe 14 B are compared with those of the R 2 Fe 14 C (R = rare earth element). Special emphasis is laid on the anisotropy behaviour. The carbides have a lower c lattice parameter, a lower ordering temperature T c and a generally higher 3d-anisotropy than the borides. The saturation magnetization is of comparable size.

Magnetocrystalline anistropy of Y3Fe27.4Ti1.6

Abstract A spinning-sample-magnetic-alignment method has been used to align fine-powdered ( μ m) Y 3 Fe 27.4 Ti 1.6 . A nearly perfect magnetic alignment was confirmed by X-ray diffraction on magnetically-aligned sample. The easy magnetization direction of Y 3 Fe 27.4 Ti 1.6 is determined to be within the (204) plane and has angle of 60° to the c -axis. The anistropy field H A of Y 3 Fe 27.4 Ti 1.6 was determined, from 4.2 K to the Curie temperature, directly on the magnetically-aligned sample by using the SPD technique in a pulsed-field magnetometer. The Curie temperature of the Y 3 Fe 27.4 Ti 1.6 was determined by measuring the temperature dependence of the ac susceptibility from 300 to 800 K. The presence of a small amount of a Y(Fe,Ti) 12 phase in the Y 3 Fe 27.4 Ti 1.6 sample is traced by susceptibility measurements.

Magnetic anisotropy and magnetic phase transition of RFe/sub 12-x/M/sub x/ (M=Ti or V)

Singular point detection technique and the AC susceptibility measurements have been used to determine the temperature dependence of the magnetocrystalline anisotropy field from 4.2 K to the Curie temperature and the temperature-induced magnetic phase transition of RFe/sub 11/Ti and RFe/sub 10/V/sub 2/ compounds. A comparison of the magnetic properties of these two series compounds has been made in details. >

Magnetocrystalline anisotropy of SmFe12 − xMox compounds with x = 0.5, 1.0, 1.5, 2.0 or 3.0

Abstract The magnetic anisotropy fields of SmFe12 − xMox compounds with x = 0.5, 1.0, 1.5, 2.0 or 3.0 were determined up to the Curie temperature using the SPD technique. An anomalous increase in the magnetization was detected at 4.2 K in the compounds with x = 1.0, 1.5 or 2.0 by measuring the magnetization on magnetically aligned samples with external fields applied parallel or perpendicular to the alignment direction.