Magnetic properties and magnetocaloric effects of La_(1-x)R_xFe_(1105) Si_9105)(R=Pr,(0≤x≤0.5);R = Ce and Nd, (0≤x≤0.3)) compounds are investigated.Partially replacing La with R = Ce,Pr and Nd in La_(1-x)R_xFe_(11.5)Si_(1.5) leads to a reduction in Curie temperature due to the lattice contraction.The substitution of R for La causes an enhancement in field-induced itinerant electron metamagnetic transition,which leads to a remarkable increase in magnetic entropy change△S_m and also in hysteresis loss.However,a high effective refrigerant capacity RC_(eff) is still maintained in La_(1-x)R_xFe_(11.5)Si_(1.5).In the present samples,a large△S_m and a high RC_(eff) have been achieved simultaneously.
Effects of Nd-doping on the magnetic properties and magnetocaloric effects (MCEs) of Nd x La 1 x Fe 11.5 Al1.5 have been investigated. Substitution of Nd leads to a weakening of the antiferromagnetic (AFM) coupling and an enhancement of the ferromagnetic (FM) coupling. This in turn results in a complex magnetic behaviour for Nd 0.2 La 0.8 Fe 11.5 Al1.5 characterized by the occurrence of two phase transitions at ～188 K (PM–AFM) and ～159 K (AFM–FM). As a result, a table-like MCE (9 J/kg·K) is found in a wide temperature range (160–185 K) for a field change of 0–5 T around the transition temperature, as evidenced by both the magnetic and calorimetric measurements. Based on the analysis of low-temperature heat capacity, it is found that the AFM–FM phase transition modifies the electron density significantly, and the major contribution to the entropy change comes from the electronic entropy change.
X-ray powder diffraction,resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1-x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm.The field-cooled temperature dependence of the magnetization curves shows that,at low temperatures,NdFe2Si2 is antiferromagnetic,while the other compounds show ferromagnetic behaviour.The substitution of Fe for Mn leads to a decrease in lattice parameters a,c and unit-cell volume V .The Curie temperature of the compounds first increases,reaches a maximum around x = 0.7,then decreases with Fe content.However,the saturation magnetization decreases monotonically with increasing Fe content.This Fe concentration dependent magnetization of Nd(FexMn1-x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe.The temperature’s square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature,which is typical of simple metals.
Our recent studies of the crystal structures, phase transitions, and magnetic properties of intermetallic compounds R5M4 (R = rare earths; M = Si, Ge) are reviewed briefly. First, crystal structures, phase relationships, and magnetic properties of several 5:4 compounds, including Nd5Si4xGex , Pr5Si4xGex, Gd5xLaxGe4,La5Si4, and Gd5Sn4 , are presented. In particular, the canted spin structures as well as the magnetic phase transitions in Pr5Si2Ge2 and Pr 5 Ge 4 investigated by neutron powder diffractions and small-angle neutron scattering are reviewed. Second, the crystal structures and magnetic properties of the most studied compounds Gd5(Si,Ge)4 are summarized. The focus is on the parent compound Gd5Ge4 , which is an amazing material exhibiting magnetic anisotropy, angular dependent spin-flop transition, metastable magnetic response, Griffiths-like phase, thermal effect under pulsed fields, antiferromagnetic and ferromagnetic resonances, pronounced effects of impurities, and high-field induced magnetic transitions.
