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Terbium (Tb) and Thulium (Tm) co-doped strontium hexaferrites (SHFs), with composition SrFe 12-2x Tb x Tm x O 19 (0.00 ≤ x ≤ 0.04), were prepared via sol-gel auto-combustion method. The effect of Tb3+ and Tm3+ (as co-dopants) on SHFs were investigated in detail. XRD pattern of the prepared SHFs revealed the formation of M-type SHFs. A secondary phase of Fe 2 O 3 starts to appear for x ≥ 0.02. The optical band gaps (E g) of the prepared SHFs were widened with the increase in doping levels. Mössbauer study showed that the Tm3+ and Tb3+ ions have the preference to occupy 12k and 2a octahedral sites. M(H) measurements were recorded at room temperature (RT; T = 300 K) and low temperature (T = 10 K). The hysteresis loops of various SHFs revealed their ferrimagnetic (FM) nature at both RT and 10 K. Magnetic parameters including saturation magnetization (M s), remanence (M r), coercivity (H c), squareness ratio (SQR = M r /M s) and magnetic moment ( n B ) were determined. Compared to the pristine (undoped) sample, lower content of Tm3+ and Tb3+ co-substitution (x = 0.01) improves significantly the magnetic properties of SHFs. With further increasing co-substitution contents (x > 0.01), an impurity phase appears and as a result the magnetization reduces. The observed SQR values of the proposed SHFs above 0.5 clearly indicated their single domain character with uniaxial magnetocrystalline anisotropy. Our systematic synthesis strategy and characterization may constitute a basis for achieving high quality co-doped SHFs in a customized way. [ABSTRACT FROM AUTHOR]

The effects of Fe substitution on the structural and magnetic properties of the HoCo 12- x Fe x B 6 (0 ≤ x ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi 12 B 6 -type structure, the lattice constants increasing linearly with x. These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for x = 0–105 K for x = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition. • Ferrimagnetic ground state. • Compensation point. • Spin reorientation transition. • Magnetocrystalline anisotropy. • Monotonic decrease of T C , T SR and M S upon Fe for Co substitution. [ABSTRACT FROM AUTHOR]

Crystal structure, magnetostriction, magnetic and magnetothermal properties have been studied for novel non-stoichiometric ErFe 2 Mn x (0 ≤ x ≤ 0.6) compounds. It has been found that for х ≤ 0.4 the compounds crystallize with MgCu 2 -type structure. Curie temperature and magnetic moment values decrease with manganese alloying. Molecular field coefficients have been calculated within ferrimagnetic two-sublattice molecular field model. Magnetic and heat capacity measurements have been used to calculate magnetocaloric effect in a wide temperature range. It has been demonstrated that increasing the Mn content in ErFe 2 Mn x leads to a significant increase (up to 39 %) of anisotropic magnetostriction value at 77 K in magnetic field of 18 kOe. At the same time, the value of effective magnetocrystalline anisotropy decreases. Thus, manganese alloying opens new way for tuning magnetocrystalline anisotropy and magnetostriction in Laves phase compounds. [Display omitted] • single phase non-stoichiometric ErFe 2 Mn х compounds are formed up to Mn concentration x = 0.4. • ErFe 2 Mn х compounds with x ≤ 0.2 have the compensation temperatures at М (Т) curves. • Curie temperature and magnetic moment values decrease with manganese alloying. • The value of anisotropic magnetostriction significant increase with increasing the Mn content. • The value of effective magnetocrystalline anisotropy decreases with increasing the Mn content. [ABSTRACT FROM AUTHOR]