Coercivity analysis in R17Fe83−χBχ magnets

We studied the coercivity in magnets of composition R₁₇Fe_83−χB_χ (R = Nd, Pr and χ = 8, 30), using measurements of the coercive field H_c, its angular dependence, and the magnetic viscosity coefficient S_v, for temperatures between 4.2 and 500 K. The results are discussed in relation to a model which does not specifically consider the detailed mechanisms involved in magnetization reversal, but which provides information about the magnetic properties in the activation volume v where magnetization reversal is initiated. It is concluded that the ordering temperature in v tends to be slightly smaller than in the bulk and that the room temperature anisotropy in v is not strongly reduced with respect to the bulk value. Finally, a direct evaluation of the dipolar interactions is in good agreement with results obtained from H_c(T).     

Magnetic properties of NdSb,GdSb, TbSb,DySb, HbSb and ErSb under hydrostatic pressure

The hydrostatic pressure dependence of magnetic properties are reported for antiferromagnetic RSb where R = Nd, Gd, Tb, Dy, HoorEr. Measurements were made for pressures 0 ≤ p ≤ 10 kbar, magnetic fields 0 ≤ H₀ ≤ 60 kG, and temperatures 1.4 K ≤ T ≤ 35 K. dT_N/dP shows no systematic trend and ranges from -0.038 K/kbar for DySb to + 0.21 K/kbar for NdSb. The magnetic properties of DySb are strongly P-dependent, whereas those of HoSb are P-independent, but sample-dependent.     

Superconducting properties of amorphous transition metal alloys

We have co-sputtered amorphous films of several Mo and W-based superconducting alloys. Measurements of T_c, ($\text{d}\text{H}{}_{\mathrm{c2}}\text{d}\text{T}$)_Tc and the normal state resistivity near T_c were made on a number of these alloys. Our results and other data from the literature are studied to examine the correlation between T_c and the dressed density of states at the Fermi level.     

Effect of Ti and C additions on structural and magnetic properties of (Pr,Nd)–Fe–B nanocrystalline magnetic materials

Effects of titanium carbide (TiC) addition on structural and magnetic properties of isotropic (Pr,Nd)–Fe-B nanocrystalline magnetic materials have been investigated. In this work, we investigate the effect of TiC addition on a (Pr,Nd)-poor and B-rich composition, as well as on a B-poor and (Nd,Pr)-rich composition. Rapidly solidified (Pr,Nd)–Fe–B alloys were prepared by melt-spinning. The compositions studied were (Pr_1−xNd_x)₄Fe₇₈B₁₈ (x=0, 0.5, and 1) with addition of 3 at% TiC. Unlike the (Pr_xNd_1−x)_9.5Fe_84.5B₆ materials that present excellent values for coercive field and energy product, the (Pr,Nd)-poor and B-rich composition alloys with TiC addition present lower values. Rietveld analysis of X-ray data and Mössbauer spectroscopy revealed that samples are predominantly composed of Fe₃B and -Fe. For the RE-rich compositions (Pr_xNd_1−x)_9.5Fe_84.5B₆ (x=0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3 at% TiC, the highest coercive field and energy product (8.4 kOe and 14.4 MGOe, respectively) were obtained for the composition Pr_9.5Fe_84.5B₆.     

Inter-relation between reversible and irreversible magnetization components in nanocrystalline SmCo films

A study of the experimental behavior of the reversible (M_rev) and the irreversible (M_irr) DCD magnetization components in enhanced-remanence SmCo films was carried out. The evolution of the DCD M_rev and M_irr components were determined at room temperature by measuring sets of first-order reversal curves from different points on the initial magnetization curve and the demagnetization curve. From these data, M_rev(M_irr)_Hi curves were built, H_i being the internal field of the sample. Recent studies show that the behavior of the M_rev(M_irr) curves at a constant internal field can be used as an indicator of the mechanism of reversal magnetization. The non-monotonic behavior showed by these curves at low fields in our material, seems to be associated with an incoherent mechanism of magnetization reversal in the nanograins of SmCo.     

Antiferromagnetism in K2[FeCl5(H2O)] and its dependence upon hydrostatic pressure

We have measured the isothermal magnetization M of antiferromagnetic K₂[FeCl₅(H₂O)] as a function of applied magnetic field H, for fields up to 80 kOe and for several hydrostatic pressures up to P ～ 10 kbar. We obtained the P =1 atm exchange parameters of this material for an orthorhombic model. The spin-flop boundary of K₂[FeCl₅(H₂O)] was studied for several pressures. For the spin-flop fields H_SF, a relation of the form $\text{H}{}_{\mathrm{SF}}\text{(T) = H}{}_{\mathrm{SF}}\text{(0) (1 + BT}\text{3}\text{2}\text{+ CT}{}^2\text{+ DT}\text{5}\text{2}\text{)}$ adequately describes the experimental points up to relatively high temperatures, for all pressures. The isotherms H_SF vs. P show an abrupt change of slope at P ? 1 kbar, possibly due to a pressure-induced exchange of the intermediate and hard magnetic axes.     

Pressure dependence of the magnetic transition fields of the quasi two-dimensional antiferromagnet (C2H5NH3)2 CuCℓ4

Using magnetic susceptibility measurements, we have studied the pressure dependence of the magnetic transition fields of powder samples of antiferromagnetic (C₂H₅NH₃)₂CuC?₄, for hydrostatic pressures up to P ～ 7 kbar. The spin-flop field H₁ decreases linearly with pressure $\text{(}\text{dH}{}_1\text{dP}\text{= ?(20±4)}\text{G}\text{kbar}\text{)}$, while the field corresponding to the paramagnetic transition H₂ shows an increase, ～ 70% for P～7 kbar, that is roughly quadratic with P.     

Quantum oscillations of the velocity of sound in zinc

Large amplitude quantum oscillations of the longitudinal sound velocity, |ΔV/V| ～ 10^-3, were observed in single crystal zinc. The effective masses associated with the ‘cigar’ and ‘butterfly’ were determined from the temperature dependence of the amplitudes of the oscillations in the region 1.5?T?4.2K. The experimental data are compared with the results of theoretical treatments.     

Electron back scattered diffraction study of SmCo magnets

The remanence and energy product of permanent magnets is a strong function of their crystallographic texture. Electron back scattered diffraction (EBSD) is a tool for texture analysis providing information about the atomic layers up to 50 nm below the surface of the material. This paper discusses experimental requirements for performing EBSD measurements on rare-earth permanent magnets and presents results on commercial SmCo magnet material. EBSD measurements proved to be very sensitive to misaligned grains and were sensitive to texture in good agreement with information provided by X-ray diffraction scans. Results for nanostructured Sm(CoFeCuZr)_z magnets are also discussed.