In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Electrical, magnetic, and Hall properties of AlxCoCrFeNi high-entropy alloys

Studies of bulk MgCu2-type rare-earth iron compounds with Laves phase are reviewed. The relationship between magnetostriction and structural distortion and the consequent crystallographic method for measuring magnetostriction are introduced at first. Then we review recent progress in understanding bulk magnetostrictive Laves phase materials, especially the magnetostriction and the minimization of the anisotropy of the light rare-earth Pr- and Sm-based compounds. Finally, a summary and outlook for this kind of compounds are presented.

https://iopscience.iop.org/article/10.1088/1674-1056/22/7/077507/pdf

Progress in bulk MgCu2-type rare-earth iron magnetostrictive compounds

In situ high-pressure x-ray diffraction, low-temperature resistivity, and magnetization experiments were performed on a La32Ce32Al16Ni5Cu15 bulk metallic glass (BMG). A sudden change in compressibility at ≈14 GPa and a rapid increase of resistivity at ≈12 K were detected, whereas magnetic phase transformation and magnetic field dependence of the low-temperature resistivity do not occur at temperatures down to 4.2 K. An interaction between conduction electrons and the two-level systems is suggested to explain the temperature and field dependences of resistivity of the BMG alloy. Although the cause of the unusual change in compressibility at ≈14 GPa is not clear, we believe that it could be linked with the unique electron structure of cerium in the amorphous matrix. An electronic phase transition in BMG alloys, most likely a second-order amorphous-to-amorphous phase transition, is suggested.

/pdf/anomalous-compression-behavior-in-lanthanum-cerium-based-11xhbx1bdh.pdf

Anomalous compression behavior in lanthanum/cerium-based metallic glass under high pressure.

Chapter 4 Magnetism and processing of permanent magnet materials

The effect of Ga substitution for Fe in R2Fe17 (R=Y, Sm, Gd, Tb, Dy, Ho, Er, and Tm) compounds on the structure and magnetocrystalline anisotropy has been studied by means of x‐ray diffraction and magnetization measurements. Both iron sublattice anisotropy and rare earth sublattice anisotropy are found to be modified by the introduction of the gallium atoms. A uniaxial anisotropy is shown in R2Fe17−xGax (for R=Y, Gd, Tb, Dy, Ho, Er, and Tm) compounds with high Ga concentration, whereas a reversal change in the easy magnetization direction is observed in the samples for R=Sm. The contributions to the uniaxial orientation of the magnetization in these compounds result from not only the rare earth sublattice, but also the iron sublattice.

/pdf/structure-and-magnetocrystalline-anisotropy-of-r2fe17-xgax-4gnxfq0xc4.pdf

Structure and magnetocrystalline anisotropy of R2Fe17−xGax compounds with higher Ga concentration

The structural and magnetic properties of compounds in the series Sm2Fe15Al2Cx have been investigated by means of x-ray diffraction (XRD) and magnetization measurements. Samples with x=0, 0.5, 1.0, 1.5, and 2.0 were prepared by the arc-melting method. XRD patterns indicate that these carbides are single phase with a rhombohedral Th2Zn17-type structure, except for Sm2Fe15Al2, which contains a few per cent of BCC alpha -Fe. The saturation magnetization for all samples is about 110 emu g-1 and has a small dependence on C concentration. The Curie temperature Tc enhancement is about 190 K for x=1.5 compared with that of Sm2Fe17. All compounds exhibit an easy c-axis anisotropy at room temperature and the anisotropy field increases to about 110 kOe when x<or=1.5. The substitution of Al, like Ga and Si, is found to not only help the formation of high-C-concentration rare-earth-Fe compounds with 2:17-type structure, but also increase the anisotropy field.

https://iopscience.iop.org/article/10.1088/0953-8984/6/14/001/pdf

The formation and magnetic properties of Sm2Fe15Al2Cx (x=0-2.0) compounds prepared by arc melting

Measurements of x-ray diffraction, magnetization, magnetostriction, and M\"ossbauer effect were made on a series of ${\mathrm{Sm}}_{088}$${\mathrm{Dy}}_{012}$(${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${)}_{2}$ polycrystalline samples (x=00, 02, 04, 06, 08, 10) It was found that the system has the cubic ${\mathrm{MgCu}}_{2}$ structure over the whole range and the lattice constant decreases with increasing x Initially, replacement of Fe results in a slight increase in both the saturation magnetization ${\mathit{M}}_{\mathit{S}}$ and Curie temperature ${\mathit{T}}_{\mathit{C}}$, while further substitution causes a decrease in ${\mathit{M}}_{\mathit{S}}$ and ${\mathit{T}}_{\mathit{C}}$ with x Results of M\"ossbauer effect study at room temperature show that the easy axes of magnetization remain in the [111] direction for all the samples The concentration dependence of the average hyperfine field, ${\mathit{H}}_{\mathrm{hf}}$ shows a similar trend as that of ${\mathit{M}}_{\mathit{S}}$ and ${\mathit{T}}_{\mathit{C}}$, exhibiting a maximum at x=04 due to the increase of the magnetic moment of the Fe atom caused by the adding of cobalt The spin-orientation diagram in ${\mathrm{Sm}}_{088}$${\mathrm{Dy}}_{012}$(${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${)}_{2}$ was determined by measurements of M\"ossbauer effect and magnetization, showing that Co substitution lowers the spin-reorientation temperature It was also found from x-ray measurement that the spontaneous magnetostriction ${\ensuremath{\lambda}}_{111}$ increased due to Co substitution, while monotonic decrease of the saturation magnetostriction ${\ensuremath{\lambda}}_{\mathit{s}}$ with Co content was observed and can be attributed to the increase of ${\ensuremath{\lambda}}_{100}$ with opposite sign to ${\ensuremath{\lambda}}_{111}$, which may be caused by the filling of the d band due to Co substitution \textcopyright{} 1996 The American Physical Society

Effect of Co substitution for Fe on magnetic and magnetostrictive properties in Sm0.88Dy0.12(Fe1-xCox)2 compounds.

X-ray diffraction (XRD) and magnetization measurements were performed to investigate the effect of Ga substitution for Co on the structural and magnetic properties of Gd2Co17−xGax compounds (x=0, 1, 2, 3, 4, 5, 6, 7, and 8) Crystal-structure studies indicate that all samples are single phase with the rhombohedral Th2Zn17-type structure except for the samples with x=7 and 8, which contain a small amount of Co The Ga substitution for Co in Gd2Co17 compounds leads to a monotonic increase in the unit cell volume and an approximately linear decrease in the saturation magnetization The Curie temperature TC is found to decrease monotonically from 1210 K for x=0 to 30 K for x=8 The compensation points are observed for the Gd2Co17−xGax samples with x=5 and 6 The value of the compensation temperature, determined from the temperature dependence of the magnetization measured in a magnetic field of 1000 Oe, is 120 and 152 K for x=5 and 6, respectively It is noteworthy that the substitution of Ga for Co in the Gd

The magnetic properties of Gd2Co17−xGax compounds

Iron‐rich intermetallic compounds Sm2Fe17−xSix and Sm2Fe17−xSixC (x=0, 1, 2, and 3) were studied The as‐prepared compounds are single phase with the rhombohedral Th2Zn17‐type structure except for Sm2Fe17C and Sm2Fe16SiC which contain some amounts of α‐Fe The unit cell volumes and saturation magnetization at room temperature are found to decrease linearly with increasing Si concentration x The Curie temperature Tc is found first to increase and then to decrease with increasing Si content X‐ray diffraction measurements on magnetically aligned powder samples show that the easy magnetization direction of the Sm2Fe17−xSix samples with x≤2 is planar while that of the sample with x=3 is conical The Sm2Fe17−xSixC samples with x≤3 exhibit an easy c‐axis anisotropy at room temperature The anisotropy field is 83 kOe for x=0 and it rises to 110 kOe at x=1, and then drops with increasing Si concentration to 55 kOe at x=3

Hua-yang Gong

Papers

Structure and magnetocrystalline anisotropy of R2Fe17−xGax compounds with higher Ga concentration

The formation and magnetic properties of Sm2Fe15Al2Cx (x=0-2.0) compounds prepared by arc melting

Effect of Co substitution for Fe on magnetic and magnetostrictive properties in Sm0.88Dy0.12(Fe1-xCox)2 compounds.

The magnetic properties of Gd2Co17−xGax compounds

Magnetic-properties of sm2fe17-xsix and sm2fe17-xsixc compounds