Spin Reorientation Transition And The Microwave Properties Of Intermetallic Compounds Of Nd(Fe_1-xCo_x)₁₀V₂

The property of traditional high frequency magnetic materials obeys the Snoek limit, thus it is hard to improve. This study is based on principle of the rare earth-3d intermetallic compounds particles with planar magnetocrystalline anisotropy can exceed the limitation of the Snoek limit. Under the common acting of a small in plane anisotropic field and a rather large out of plane anisotropic field, which can get a higher permeability without a badly descent of resonance frequency.Using the Vanadium as a stabilizing element, and using the Cobalt to substitute the iron, The ThMn12-type rare earth-3d intermetallic compounds of Nd(Fe1-xCox)10V2 were prepared by means of vacuum arc melting, subsequent vacuum annealing, then they were ball milling for 12 hours. The influence of the substitution of Cobalt for iron on the structure and statistic magnetic properties of these compounds is investigated by X-ray powder diffraction and magnetic measurements. The paraffin composites were prepared by mixing paraffin with compounds particles and pressing into toroidal shape, so that the relative complex permeability of the composites has been measured in the range of 0.1-10 GHz. The mechanism of relative complex permeability affected by the change of anisotropy in high frequency has been discussed. The main research contents and results are shown as follows:(1) The structure of Nd(Fe1-xCox)10V2 compounds is a single phase with tetragonal ThMn12-type structure in a range of x=0-0.5. The lattice constants and unit-cell volume decrease monotonically with increasing of Co concentration, due to Cobalt atom radius is smaller than iron.(2) The saturation magnetization of Nd(Fe1-xCox)10V2 compounds increase from 115 emu/g (x=0) to 122 emu/g (x=0.2) at first and then decrease to 96 emu/g (x=0.5) with increasing Co concentration while the coercivity of the compounds are decreasing firstly and then keep constant, then it increased abruptly. The easy magnitization direction of the compounds also changed with the Co content from c-axial (x=0) to a-b plane(x=0.2), and return to c-axial when x=0.5.(3) The Curie temperature (Tc) of Nd(Fe1-xCox)10V2 compounds increase monotonically from 570 K (x=0) to 676 K (x=0.4) with increasing of Co concentration, but it decreased to 662 K (x=0.5)when further increase the Co content. The decrease of interatomic distances and a preferential substitution of Co for Fe in regions where there is negative exchange could account for the strengthening of exchange interaction and thus for an enhancement of Tc,(4) The M-T curves show that the temperature of spin reorientation transition (SRT) ascent quickly with increasing the Co concentration:below the room temperature, the temperature of SRT increased from 120 K (x=0) to 280 K (x=0.4); Above the room temperature, there was no SRT when x=0, while the SRT appeared after Co enter the compounds, and its temperature increased with increasing of Co content till x=0.4, when x=0.5 the temperature of SRT decreased and the transition is different with before. It is account for the Co substitution weakens the anisotropy of Fe sublattice.(5) By the Mossbauer measurement, the V atom preferes to occupy the 8i sites. When Co atom substituted the Fe atom, the Co appeared to occupy the 8f and 8j sites, this is account for the 8f and 8j sites have smaller interatomic distances and this occupation made the system with low enthalpy. The Isomer Shift (IS) of 8i and 8j sites increased obviously while that of 8f sites was almost constant. The Quadrupole Splitting (QS) value changed abruptly in 8f sites between x=0 and x=0.15, as well as in 8i sits between x=0.4 and x=0.5, which means the transition of the easy magnetization direction exists in these ranges.(6) For the paraffin composites with 35 vol.% of Nd(Fe1-xCox)10V2, both of real and imagine part of the permittivity was almost constant in our measurement frequency range, and for different x, the value did not change a lot neither, however the complex permeability varied with the increasing of Co concentration, the real part of permeability at low frequency was 2.2 for x=0, and then it ascend to 3.2 for x=0.2, when x=0.5, it drops to 2.3; the imagine part of permeability has no resonance peak for x=0 and x=0.5, and the eddy current loss is the main loss, but there was a resonance peak for x=0.15-0.4, and the loss was caused by nature resonance, that is in respect that the permeability has a relationship with anisotropy, when anisotropy changed, the permeability would change too.(7) The absorbing properties of the Nd(Fe1-xCox)10V2 with plane anisotropy were much better than the ones with uniaxial anisotropy.