Isotropic and anisotropic magnetoelastic interactions in heavy and light RCo₂Laves phase compounds

Abstract

The thermal expansion and anisotropic magnetomiction of the R C q Laves phases were studied in the temperature range 4-500 K using the x-ray powder diffraction methcd.In the heavy RCo2 the magnetic moment of the itinerant d electron subsystem derived imm the magnetovolume effect was found to fit well with the magnetization curve of YCo2. A pronounced paraprocess above the metamagnetic m i t i o n has been observed when increasing the f-d exchange field. "%e type and temperature variation of the distortion of the njbic unit cell of the t h ~ compounds PrCol, NdCo2 and SmCoz have been studied in detail. The corresponding magnetostriction ~nslants 1111 or AIM were calculated. At 4 K the following values have been obtained: R c 0 2 . temgonai distortion. easy axes (100). AIM = -3.4 x SmCq, rhombohedral distortion, easy axes (Ill), A l l , r -4.6 x NdC4, teuagonal distortion and eaxy axes (100) for 42 K c I e T,. orthorhombic distortion and easy axes (110) for T c 42 K with 111111 = 1.9 x aid AIM = -4.0 x IO-' .

Itinerant electron metamagnetism and magnetocaloric effect in Dy(Co,Si)2

“…DyðCo 12x Si x Þ 2 can be classified as a narrow domain wall system due to the fact that the ordering temperature is much smaller (compared to DyFe 2 ). Also, the anisotropy is large due to the magneto-elastic distortions taking place at the T C ; as the sample is cooled from high temperatures [17,18]. Therefore, it is quite possible that the present system exhibits domain wall pinning effect and consequently a large thermomagnetic irreversibility.…”

Multiferroic (ferroelastic/ferromagnetic/ferrimagnetic) aspects of phase transitions in RCo2Laves phases

“…Figure 1 shows their characteristic pattern of transitions with changing number of 4f electrons, assuming all the ions to be in their usual 3+ state. The paramagnetic high temperature parent cubic structure gives way to ferromagnetic (R = Pr, Nd, Sm) or ferrimagnetic (R = Gd, Tb, Dy, Ho, Er, Tm) ordered structures at phase transitions which are marked also by symmetrybreaking shear strains and positive volume strains [2][3][4][5][6][7]. The magnetism is dominated by the R sublattice, with essentially temperature-independent magnetic moments.…”

“…The magnetic ordering temperatures are proportional to the de Gennes factor, Figure 1. Summary of magnetic phase transitions in RCo 2 Laves phases; data for GdCo 2 , TbCo 2 , DyCo 2 , HoCo 2 and ErCo 2 from [3], data for PrCo 2 , SmCo 2 and TmCo 2 from [4], data for NdCo 2 from [7].…”

Magnetostriction and transformation of crystal structure of intermetallic compound NdCo2

“…They usually have gigantic values of the magnetocaloric effect, magnetostriction and magnetoresistance [2][3]. Among these materials there are RCo2 compounds, in which there is a sharp dependence the magnetic phase transitions from the lattice parameters [5][6][7][8][9]. Transformation of the crystal and magnetic structure as a result of magnetic phase transitions in NdCo 2 on polycrystalline samples was studied in [1], with methods of X-ray and neutron diffraction.…”

“…Transformation of the crystal and magnetic structure as a result of magnetic phase transitions in NdCo 2 on polycrystalline samples was studied in [1], with methods of X-ray and neutron diffraction. Temperature dependence of the magnetostriction constants λ 100 for RCo 2 was calculated by measuring the lattice constant in [1,8,10] and it was shown that λ 100 for NdCo 2 reaches very high values of λ 100 =-3.2·10 -3 . However there is no data about the temperature dependence of linear and volume magnetostriction induced by magnetic field in NdCo 2 .…”