Magnetic and magnetocaloric properties of SmxGd1-xMn2Si2

The magnetic and magnetocaloric properties of Gd1-xSmxMn2Si2 compounds with 0 < x <= I have been studied to determine their suitability as magnetic refrigerant materials. The rare earth ordering temperatures are found to decrease from 60 K for x = 0 to 37 K for x = 1. The temperature variations of magnetization under 'field-cooled' and 'zero-field-cooled' conditions are found to differ slightly, indicating a small thermomagnetic irreversibility. Magnetocaloric effect is calculated in terms of isothermal magnetic entropy change (Delta S-M) using the magnetization isotherms. The maximum values of Delta S-M are found to be 5.9 J kg(-1) K-1 in GdMn2Si2, and 3.4 J kg(-1) K-1 in SmMn2Si2. (c) 200

Magnetic and magnetothermal properties of La(1-x)Nd(x)Fe(11.5)Al(1.5) compounds

In this paper, we report the structural, magnetic, and magnetocaloric effect (MCE) of La(1-x)Nd(x)Fe(11.5)Al(1.5) (x=0.1,0.2) compounds. Temperature dependence of magnetization data shows that with Nd substitution, the nature of magnetic transition changes from second order transition to multiple first order transition. This observation is confirmed by the thermodynamic analysis using the Landau theory of phase transitions. The MCE has been calculated in terms of the isothermal magnetic entropy change (Delta S(M)) using the magnetization isotherms obtained at temperatures close to the transition temperature. The maximum values of Delta S(M) are found to be 5.4 and 4.6 J kg(-1) K(-1) of x=0.1 and x=0.2, respectively, for a field change of 50 kOe, whereas the value for the undoped compound is about 3 J kg(-1) K(-1). The refrigerant capacity has been calculated to be 544 J/kg K for x=0.1 and 470 J/kg K for x=0.2. (C) 2008 American Institute of Physics

Magnetocaloric and magnetotransport properties of R(2)Ni(2)Sn compounds (R = Ce, Nd, Sm, Gd, and Tb)

We report a detailed magnetic, magnetocaloric, and magnetotransport study on R(2)Ni(2)Sn compounds with different rare earths. The magnetic state of these compounds is found to be complex because of the coexistence of ferromagnetic and antiferromagnetic components. These compounds show phenomena such as multiple magnetic transitions, nonsaturation of magnetization, and metamagnetic transitions. Analysis of the zero-field heat capacity data shows that the magnetic entropy is less than the theoretical value, indicating the presence of some moment on Ni. Schottky anomaly is present in the magnetic heat capacity data of Sm(2)Ni(2)Sn. The temperature variation of magnetocaloric effect reflects the magnetization behavior. Tb(2)Ni(2)Sn and to a less extent Gd(2)Ni(2)Sn show oscillatory magnetocaloric effect. The variation of magnetocaloric effect is correlated with the ferromagnetic-antiferromagnetic phase coexistence. The electrical resistivity analysis has shown that the electron-magnon scattering is prominent at low temperature, while phonon scattering modified by the s-d interaction is crucial at high temperatures. The magnetoresistance is very large in Ce(2)Ni(2)Sn and shows a quadratic dependence on the field, implying the role of spin fluctuations in determining the transport behavior. Large magnetoresistance has been observed in other compounds as well

Investigations on magnetic and magnetocaloric properties of the intermetallic compound TbAgAl

Magnetic and magnetocaloric properties of the intermetallic compound TbAgAl have been investigated. Temperature dependence of magnetization data revealed that TbAgAl exhibits magnetic ordering at 59 K and possesses competing ferromagnetic-antiferromagnetic interactions, which leads to the formation of Griffiths-like phase. The field dependence of magnetization data shows the existence of a metamagnetic-like transition at a critical field of 10 kOe. Unusually potent relaxation effects are seen in the time dependence of magnetization data in the ordered phase. The presence of spin-glass-like state is found to affect magnetocaloric properties of this compound

Magnetocaloric effect in RCo(2)-based systems effect of spin fluctuations

The variation of magnetocaloric effect, calculated both in terms of isothermal magnetic entropy change and adiabatic temperature change, in various RCo(2)-based compounds is discussed. Effect of spin fluctuations on the magnetocaloric effect in these compounds is analyzed. Origin of various contributions that give rise to spin fluctuations is studied in the light of a recent theoretical model

Correlation between magnetism and magnetocaloric effect in the intermetallic compound DyNiAl

Magnetization studies carried out in polycrystalline sample of DyNiAl show the presence of two magnetic transitions, one at 15 K and the other at 30 K. The low-temperature transition is attributed to the onset of antiferromagnetic ordering, while the other one corresponds to the ferro-para transition. Thermomagnetic irreversibility found in the temperature dependence of magnetization data is attributed to the domain-wall pinning effect and also to the magnetic frustration. Magnetocaloric effect is found to be negative in the antiferromagnetic phase and positive above the Neel temperature. (C) 200

Structural and magnetic properties of ErTiCo11-xAlx

ErTiCo11-xAlx compounds with ThMn12 structure were synthesized for x less than or equal to 3. The crystal structure was analyzed and the bond lengths were calculated using the Rietveld refinement technique. With Al substitution, the lattice parameter and unit-cell volume are found to increase. Ti atoms are found to occupy 8i sites in the compounds. The saturation magnetization and the Curie temperature decrease with Al substitution. Thermomagnetic curves show spin reorientation in all these compounds. The easy magnetization direction at room temperature was found to be along a cone in the Al-substituted compounds

Effect of magnetic polarons on the magnetic, magnetocaloric, and magnetoresistance properties of the intermetallic compound HoNiAl

The magnetic, magnetocaloric, and magnetoresistive properties of the polycrystalline compound HoNiAl have been studied. The temperature variations of magnetization and heat capacity show that the compound undergoes two magnetic transitions, one at 14 K and the other at 5 K. The former is due to the paramagnetic-ferromagnetic transition, while the latter is attributed to the onset of an antiferromagnetic ordering, as the temperature is lowered. The M-H isotherm obtained at 2 K shows a metamagnetic transition with a critical filed of about 13 kOe. The maximum values of isothermal magnetic entropy change and adiabatic temperature change, for a field change of 50 kOe, are estimated to be 23.6 J/kg K and 8.7 K, respectively. The relative cooling power is found to be about 500 J/kg for a field change of 50 kOe. A large magnetoresistance of about 16%, near the ordering temperature of 14 K, is observed for a field of 50 kOe. The magnetic, magnetocaloric, and magnetoresistance data seem to suggest the presence of magnetic polarons in this compound. (C) 200