A sign of field-induced first order magnetic state transition and giant reversible A sign of field-induced first order magnetic state transition and giant reversible magnetocaloric effect in cobalt hydroxide nanosheets magnetocaloric effect in cobalt hydroxide nanosheets Abstract AbstractWe report the synthesis of β−Co(OH) 2 nanosheets using microwave assisted hydrothermal and conventional chemical reaction methods. A magnetic transition at an onset temperature, T 1 ~ 96 K, and a sign of antiferromagnetic state transition at the Néel temperature, T N =9~10 K, can be determined from M-T curves and M-H curves magnetic properties investigation. It is found that a sign of field-induced first order transition below 9 K, act as a role of reversing the magnetocaloric effect from negative to positive value. The large reversible magnetic-entropy change (∆S M ) of 17 J/kg K around 11 K for a field change of 5 T indicates that this material is useful for refrigeration applications at low temperatures. , SX (2010), A sign of field-induced first order magnetic state transition and giant reversible magnetocaloric effect in cobalt hydroxide nanosheetsWe report the synthesis of  −Co͑OH͒ 2 nanosheets using microwave assisted hydrothermal and conventional chemical reaction methods. A magnetic transition at an onset temperature, T 1 ϳ 96 K, and a sign of antiferromagnetic state transition at the Néel temperature, T N =9ϳ 10 K, can be determined from M-T curves and M-H curves magnetic properties investigation. It is found that a sign of field-induced first order transition below 9 K, act as a role of reversing the magnetocaloric effect from negative to positive value. The large reversible magnetic-entropy change ͑⌬S M ͒ of 17 J/kg K around 11 K for a field change of 5 T indicates that this material is useful for refrigeration applications at low temperatures.
(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.
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