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(2013). The magnetocaloric effect and critical behaviour of the Mn0.94Ti0.06CoGe alloy. Journal Of Physics-Condensed Matter, 25 (5), 1-7.The magnetocaloric effect and critical behaviour of the Mn0.94Ti0.06CoGe alloy AbstractStructural, magnetic and magnetocaloric properties of the Mn0.94Ti0.06CoGe alloy have been investigated using x-ray diffraction, DC magnetization and neutron diffraction measurements. Two phase transitions have been detected, at T-str = 235 K and T-C = 270 K. A giant magnetocaloric effect has been obtained at around Tstr associated with a structural phase transition from the low temperature orthorhombic TiNiSi-type structure to the high temperature hexagonal Ni2In-type structure, which is confirmed by neutron study. In the vicinity of the structural transition, at T-str, the magnetic entropy change, -Delta S-M reached a maximum value of 14.8 J kg(-1) K-1 under a magnetic field of 5 T, which is much higher than that previously reported for the parent compound MnCoGe. To investigate the nature of the magnetic phase transition around T-C = 270 K from the ferromagnetic to the paramagnetic state, we performed a detailed critical exponent study. The critical components gamma, beta and delta determined using the Kouvel-Fisher method, the modified Arrott plot and the critical isotherm analysis agree well. The values deduced for the critical exponents are close to the theoretical prediction from the mean-field model, indicating that the magnetic interactions are long range. On the basis of these critical exponents, the magnetization, field and temperature data around T-C collapse onto two curves obeying the single scaling equation M(H, epsilon) = epsilon(beta)f +/-(H/ epsilon(beta+gamma)). AbstractStructural, magnetic and magnetocaloric properties of the Mn 0.94 Ti 0.06 CoGe alloy have been investigated using x-ray diffraction, DC magnetization and neutron diffraction measurements. Two phase transitions have been detected at T str = 235 K and T C =270 K, respectively. A giant magnetocaloric effect has been obtained around T str associated with a structural phase transition from the low temperature orthorhombic TiNiSi-type structure to the high temperature hexagonal Ni 2 In-type structure, which is confirmed by neutron study. In the vicinity of the structural transition, T str , the magnetic entropy change, -∆S M reached a maximum value of 14.8 Jkg -1 K -1 under a magnetic field of 5T which is much higher than that previously reported on the parent compound MnCoGe. To investigate the nature of the magnetic phase transition around T C =270 K from ferromagnetic to paramagnetic state, we performed a detailed critical exponent study. The critical components, γ, β and δ determined using the Kouvel-Fisher method, the modified Arrott plot as well as the critical isotherm analysis agree well. The values deduced for the critical exponents are close to the theoretical prediction of the mean-field model, indicating that the magnetic interactions are long range. Based on these critical exponents, the magnetizat...

Dou, S. X. (2013). Critical phenomena and estimation of the spontaneous magnetization by a magnetic entropy analysis in Mn0.96Nb0.04CoGe alloy. Journal of Applied Physics, 113 (23), 233903-1-233903-5.Critical phenomena and estimation of the spontaneous magnetization by a magnetic entropy analysis in Mn0.96Nb0.04CoGe alloy AbstractMagnetic and magnetocaloric properties of the alloy Mn0.96Nb0.04CoGe have been investigated. According to the mean-field theory prediction, the relationship between DS M / (H/T C ) 2/3 has been confirmed in the temperature region near T C for that system. To investigate the nature of the magnetic phase transition, a detailed critical exponent study has been performed. The critical components, c, b, and d determined using the Kouvel-Fisher method, the modified Arrott plot, as well as the critical isotherm analysis agree well. Moreover, these critical exponents are confirmed by the Widom scaling law and the validity of the calculated critical exponents was also confirmed by the scaling theory. The values deduced for the critical exponents are close to the theoretical prediction of the mean-field model values, thus indicating that long range interactions dominate the critical behavior in the Mn 0.96 Nb 0.04 CoGe system. It is also speculated that the competition between the localized Mn-Mn magnetic interactions should be responsible for the critical behavior in this system. Moreover, an excellent agreement is found between the spontaneous magnetization determined from the entropy change (ÀDS M vs. M 2 ) and the classical extrapolation from the Arrott curves (H/M vs. M 2 ), thus confirming that the magnetic entropy change is a valid approach to estimate the spontaneous magnetization in this system. V C 2013 AIP Publishing LLC.

Dou, S. X. (2013). Investigation of the critical behavior in Mn0.94Nb 0.06CoGe alloy by using the field dependence of magnetic entropy change. Journal of Applied Physics, 113 (9), 093902-1-093902-5.Investigation of the critical behavior in Mn0.94Nb 0.06CoGe alloy by using the field dependence of magnetic entropy change AbstractThe critical behaviour of Mn0.94Nb0.06CoGe alloy around the paramagnetic-ferromagnetic phase transition was studied based on the field dependence on magnetic entropy change. By using the obtained exponents, the modified Arrott plot is consistent with that by using conventional method. These critical exponents are confirmed by the Widom scaling relation. Based on these critical exponents, the magnetization, field and temperature data around Tc collapse into two curves obeying the single scaling equation MðH; e)¼ebf6(H/ ebþc). The calculated critical exponents not only obey the scaling theory but also anastomose the deduced results from the Kouvel-Fisher method [ J. S. Kouvel and M. E. Fisher, Phys. Rev. 136, A1626 (1964)]. The values deduced for the critical exponents in the Mn0.94Nb0.06CoGe alloy are close to the theoretical prediction of the mean-field model, indicating that the magnetic interactions are long range. This method eliminates the drawback due to utilization of multistep nonlinear fitting in a conventional manner. So it provides an alternative method to investigate the critical behaviour. The critical behaviour of Mn 0.94 Nb 0.06 CoGe alloy around the paramagnetic-ferromagnetic phase transition was studied based on the field dependence on magnetic entropy change. By using the obtained exponents, the modified Arrott plot is consistent with that by using conventional method. These critical exponents are confirmed by the Widom scaling relation. Based on these critical exponents, the magnetization, field and temperature data around Tc collapse into two curves obeying the single scaling equation

In an effort to improve the magnetocaloric effects of the NaZn13-type La0.8Ce0.2Fe11.4Si1.6 compound, the effect of boron doping on the magnetic properties and magnetocaloric properties has been investigated. The magnetic entropy change (ΔSM) for the La0.8Ce0.2Fe11.4Si1.6 compound, obtained for a field change of 0–5 T using the Maxwell relation exhibits a spike and appears to be overestimated and is thus corrected by using the Clausius-Clapeyron equation (CC). The ΔSM determined from the CC equation is estimated to be 19.6 J kg−1K−1. However, large hysteretic losses which are detrimental to the magnetic refrigeration efficiency occur in the same temperature range. In this work, we report a significant reduction in hysteretic losses by doping the La0.8Ce0.2Fe11.4Si1.6 compound with a small amount of boron to obtain La0.8Ce0.2Fe11.4Si1.6Bx compounds. The hysteresis loss decreases from 131.5 to 8.1 J kg −1 when x increases from 0 to 0.3, while ΔSM, obtained for a field change of 0–5 T, varies from 19.6 to 15.9 J kg−1K−1. This also simultaneously shifts the TC from 174 to 184 K and significantly improves the effective refrigerant capacity (RCeff) of the material from 164 to 305 J kg−1.