Magnetic phase transitions, magnetocrystalline anisotropy, and crystal-field interactions in the RFe11Ti series (where R=Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, or Tm)

Thermodynamics and Magnetism of SmFe12 Compound Doped with Co and Ni: An Ab Initio Study

Ni-doped Sm(Fe1−xCox)12 alloys are investigated for their magnetic properties. The Sm(Fe,Co)11M1 compound (M acts as a stabilizer) with the smallest (7.7 at.%) rare-earth-metal content has been recognized as a possible contender for highly efficient permanent magnets thanks to its significant anisotropy field and Curie temperature. The early transition metals (Ti-Mn) as well as Al, Si, and Ga stabilize the SmFe12 compound but significantly decrease its saturation magnetization. To keep the saturation magnetization in the range of 1.4–1.6 T, we suggest replacing a certain amount of Fe and Co in the Sm(Fe1−xCox)12 alloys with Ni. Ni plays the role of a thermodynamic stabilizer, and contrary to the above-listed elements, has the spin moment aligned parallel to the spin moment of the SmFe12 compound, thereby boosting its saturation magnetization without affecting the anisotropy field or Curie temperature.

Recent advances in SmFe12-based permanent magnets

To realize a sustainable society, 'green technology' with low (or even zero) CO₂ emissions is required. A key material in such technology is a permanent magnet because it is utilized for electric-power conversion in several applications including electric vehicles (EVs), hybrid EVs (HEVs), and turbines for wind power generation. To realize highly efficient electric-power conversion, a stronger permanent magnet than Nd-Fe-B is necessary. One potential candidate is a Fe-rich SmFe₁₂-based compound with a ThMn₁₂ structure. In this paper, the phase stability, structure, and intrinsic and extrinsic magnetic properties in both film and bulk forms are reviewed. Based on these results, a possible way to realize a strong SmFe₁₂-based permanent magnet in bulk form is discussed.

ThMn12-type phases for magnets with low rare-earth content: Crystal-field analysis of the full magnetization process

Rare-earth (R)-iron alloys are a backbone of permanent magnets. Recent increase in price of rare earths has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. For this reason strong magnets with the ThMn12 type of structure came into focus. Functional properties of R(Fe,T)12 (T-element stabilizes the structure) compounds or their interstitially modified derivatives, R(Fe,T)12-X (X is an atom of hydrogen or nitrogen) are determined by the crystal-electric-field (CEF) and exchange interaction (EI) parameters. We have calculated the parameters using high-field magnetization data. We choose the ferrimagnetic Tm-containing compounds, which are most sensitive to magnetic field and demonstrate that TmFe11Ti-H reaches the ferromagnetic state in the magnetic field of 52 T. Knowledge of exact CEF and EI parameters and their variation in the compounds modified by the interstitial atoms is a cornerstone of the quest for hard magnetic materials with low rare-earth content.

Stress-induced magnetic domain structure in DyFe11Ti compound

In this work, we present the results of the DyFe11Ti compound magnetic domain structure (DS) exploration. It was found that mechanical polishing leads to a change of the anisotropy of the surface layer, which affects the magnetic DS configuration. It is established that the equilibrium structure of the surface domains is restored through time under unchanged external conditions. It is suggested that the mechanism of DS relaxation has thermal fluctuation nature.

Magnetic structure and spin reorientation of quaternary Dy2Fe2Si2C

We have investigated the low temperature magnetic properties of Dy₂Fe₂Si₂C by using magnetisation, specific heat, x-ray diffraction, neutron powder diffraction and ⁵⁷Fe Mössbauer spectroscopy measurements over the temperature range 1.5 K-300 K. Dy₂Fe₂Si₂C exhibits two magnetic transitions at low temperatures: an antiferromagnetic transition at [Formula: see text] K and a spin-reorientation transition at [Formula: see text] K. The magnetic structure above T _t can be described with a propagation vector [Formula: see text] with the ordering of the Dy magnetic moments along the monoclinic b-axis whereas on cooling below T _t the Dy moment tips away from the b-axis towards the ac-plane. We find that the spin-reorientation in Dy₂Fe₂Si₂C is mainly driven by the competition between the second-order crystal field term B ₂₀ and the higher-order terms, in particular B ₄₀ and B ₆₄.

High-field magnetization and magnetoelasticity of single crystalline HoFe5Al7

Magnetization and ultrasound measurements have been performed in pulsed magnetic fields up to 60 T on a ferrimagnetic HoFe5Al7 single crystal (Curie temperature TC = 216 K, compensation point Tcomp = 65 K) with a tetragonal crystal structure of the ThMn12-type. The compound exhibits a high magnetic anisotropy of the easy-plane type. A large anisotropy is also observed within the basal plane having an easy-magnetization direction along the [110] axis with the spontaneous magnetic moment Ms = 2 µB/f.u. at T = 2 K. Along the easy axis, two first-order field-induced magnetic transitions are observed. At both transitions sharp anomalies in the acoustic properties are found. The critical fields of the transitions depend on temperature in a different manner. Within molecular-field theory and using the high-field magnetization data the Ho-Fe inter-sublattice exchange parameter has been determined to be nHoFe ≈ 4 T/µB. The magnetoelasticity has also been probed by magnetization measurements under hydrostatic pressure. TC decreases with a rate dTC/dp = -10 K/GPa, whereas Tcomp increases with dTcomp/dp = 3.5 K/GPa.