ΔSM Max Research Articles

Influence of Co-Doping on Magnetic Properties and Magnetocaloric Effect of Fe-Co-Zr-Cu-B Melt-Spun Ribbons.

In this work, we investigated magnetic properties and magnetocaloric effect in Fe90-xCoxZr7Cu1B₂ (x = 0, 1, 2, 3 and 4) melt-spun ribbons. The ribbons were prepared by using a melt-spinning method with a tangential velocity of a copper wheel of 40 m·s-1. The obtained ribbons are almost amorphous. The alloys exhibit typical soft magnetic behavior with low coercivity at room temperature. A minor replacement of Fe by Co gives an increment in Curie temperature (TC) of the alloys to higher temperatures. The TC of the alloys increases from 242 to 342 K with an increase of x from 0 to 4. Maximum magnetic entropy change, ΔSm max, of the alloys, was found to be larger than 0.7 J·kg-1·K-1 in a magnetic field change ΔH of 12 kOe for all the concentrations of Co. High refrigerant capacitys (RC >100 J ·kg-1 with ΔH = 12 kOe) at room temperature region have been obtained for the alloys. The large magnetocaloric effect near room temperature suggests that the alloys can be considered as magnetic refrigerants in the range of 250-350 K.

Temperature span of magnetocaloric effect in Nb-doped La0.7Ca0.3Mn1−xNbxO3 (x=0, 0.002 and 0.01)

In this work, we report magnetocaloric effect of Nb-doped on La0.7Ca0.3Mn1-xNbxO3 (x=0, 0.002 and 0.01). Maximum magnetic entropy change under applied field of 10kOe obtained was –ΔSM max of 4.69Jkg−1K−1, 1.75Jkg−1K−1 and 1.95Jkg−1K−1 for x=0.0, 0.002 and 0.01, respectively. Total temperature span of both Nb-doped samples was 51K. A slight Nb-doped obtained a temperature span that went through the temperature span of the sample without Nb-doped, meanwhile more increasing Nb-doped might cause a little enhancement of maximum magnetic entropy change.

The residual entropy of Shastry-Sutherland lattice of rare-earth tetraborides

The experimental temperature dependence of thulium tetraboride specific heat Cp(T) and other heat capacity data for other RE-tetraborides were investigated in the 2–300 K temperature interval. Anomalies of Cp(T) dependence of TmB4 at TN1 = 9.6 K and TN2 = 11.4 K due to the antiferromagnetic ordering have been revealed. The ground state of the ion Tm3+ was confirmed as a doublet. The diffuse anomaly of Cp(T) is attributed to the Schottky contribution to the specific heat of the tetraboride, which is caused by the influence of the crystal electric field (CEF). The presence of the residual (zero-point) entropy S0 of the magnetic moments system of Tm3+ ions, due to frustration of the Shastry-Sutherland lattice, is detected. As a measure of the frustration of the system, a new characteristic of frustrated systems, the entropy frustration figure of merit, the value of which depends on the zero-point entropy of the system, is introduced: fS = S0/ΔSm max, where ΔSm max is the maximum value of entropy change of the boride magnetic subsystem. For TmB4 and tetraborides of Gd, Tb, Dy, Ho, and Er, fs values determined from thermal measurements, and f = Өc-w/TN (Өc-w denotes the Curie-Weiss temperature; TN is Neel temperature), calculated according to the magnetic measurement data, are practically identical.

Field Dependence of Magnetocaloric Properties in La 0.6Pr 0.4Fe 10.7Co 0.8Si 1.5

In this paper, the field dependence of magnetocaloric properties of La 0.6Pr 0.4Fe 10.7Co 0.8Si 1.5 with second-order phase transition material is studied using a phenomenological model. The model parameters were determined from the magnetization data adjustment and were used to give better fits to magnetic transition and to calculate the magnetocaloric thermodynamic quantities. The entropy curves have been observed to behave as an asymmetrical broadening of ΔS M peak with increasing magnetic field. For larger fields, the peak shifts to higher temperatures, while the overall shape of the curve broadens over a wide temperature range. The values of maximum magnetic entropy change, full width at half maximum, and relative cooling power, at several magnetic field variations, were calculated. The maximum magnetic entropy changes of 3.957(5) and 14.197(4) J kg −1 K −1 and the relative cooling power (RCP) values of 95.420(3) and 392.729(2) J kg −1 are obtained for 1 and 5 T, respectively. The theoretical calculations are compared with the available experimental data. The critical exponents associated with ferromagnetic transition have been determined from magnetocaloric effect (MCE) methods. By using the field dependence of ΔS M max≈a(μ 0 H) n and the distance (T peak−T c)≈b(μ 0 H)1/Δ, we have investigated the critical behavior of La 0.6Pr 0.4Fe 10.7Co 0.8Si 1.5. From the analysis of the relationship between the local exponent n and the gap exponent Δ, we have calculated other exponents: β, γ, and δ. The large MCE, relatively high RCP, high magnetization, and low cost jointly make the present compound a promising candidate for magnetic refrigerant near room temperature.

Investigation of the influence of hydrostatic pressure on the magnetic and magnetocaloric properties of Ni2−XMn1+XGa (X = 0, 0.15) Heusler alloys

The effect of hydrostatic pressure on the magnetic and magnetocaloric properties of Ni2−XMn1+XGa (X = 0, 0.15) Heusler alloys around the martensitic transformation temperature (TM) has been investigated. We find that magnetic field increases and decreases the characteristic transitions temperature for X = 0 and 0.15, respectively, and increases the saturation magnetization of martensite phase for both the alloys. However, the hysteresis width decreases for both the alloys as we increase the magnetic field to 5 T. Application of hydrostatic pressure increases (decreases) the TM for X = 0 and 0.15. Pressure stabilizes the martensite phase with the increase of TM for Ni2MnGa, whereas the austenite phase gets stabilized with the decrease of TM in Ni1.85Mn1.15Ga (x = 0.15). Metamagnetic-like transition is suppressed for both the specimens with increasing pressure. The maximum magnetic entropy change (ΔSM max) is found to reduce from 19.2 J kg−1 K−1 (P = 0) to 6.04 J kg−1 K−1 (P = 9.69 kilobars) around TM for Ni2MnGa and it decreases from 8.9 J kg−1 K−1 (P = 0) to 1.27 J kg−1 K−1 (P = 7.4 kilobars) around TM for Ni1.85Mn1.15Ga.

Effect of Fe substitution on magnetocaloric effect in borocarbide superconductor Dy(Ni1-xFex)2B2C

Abstract The magnetic properties and magnetocaloric effect (MCE) in antiferromagnetic superconductor Dy(Ni1- x Fe x )2B2C ( x = 0, 0.1, and 0.2) has been studied. The magnetic transition temperature T M as well as the temperature at the maximum of magnetic entropy change (-Δ S M max ) slightly shift to low temperature with increasing x . An inverse MCE was observed, which is attributed to the nature of antiferromagnetic state under low magnetic field and at low temperatures for the present Dy(Ni1- x Fe x )2B2C compounds. A normal large MCE was observed under higher magnetic field changes, which is related to a field-induced first order meatmagnetic transition from antiferromagnetic to ferromagnetic state. Under a magnetic field change of 7 T, the values of -ΔSM max reach 22.1, 16.6, and 14.8 J Kg -1 K -1 for x = 0, 0.1, and 0.2, respectively. The corresponding values of relative cooling power are 464, 332 and 295 J/kg. The observed large magnetic entropy is related to a field-induced first order metamagnetic transition from antiferromagnetic to ferromagnetic state.