Hangfu Yang

The Magnetic and Magnetocaloric Properties of the Perovskite La 0.7 Ca 0.3 Mn 1-x Ni x O₃

This paper studies the effects of the Mn-site substitution by nickel on the magnetic properties and the magnetocaloric properties of La 0.7 Ca 0.3 Mn 1-x Ni x O₃ (x = 0, 0.05 and 0.1). The orthorhombic crystal structures of the samples are confirmed by the room temperature X-ray diffraction. The dependence of the Curie temperature (T C ) and the magnetic entropy change (ΔS M ) on the Ni doping content was investigated. The samples with x = 0 had the first order phase transition, while the samples with x = 0.05 and 0.1 had the second order phase transition. As the concentration of Ni increased, the maximum entropy change (|ΔS M | max ) decreased gradually, from 2.78 Jㆍ㎏?¹ㆍK?¹ (x = 0) to 1.02 Jㆍ㎏?¹ㆍK?¹ (x = 0.1), in a magnetic field change of 15 kOe. The measured value of T C was 185 K, 150 K and 145 K for x = 0, 0.05 and 0.1, respectively. The phase transition temperatures became wider as x increased. It indicates that the Mn-site substitution by Ni may be used to tailor the Curie temperature in La 0.7 Ca 0.3 Mn 1-x Ni x O₃.

Effect of Zr Addition on the Magnetization Reversal Behavior for α-Fe/Pr2Fe14B Nanocomposite Alloys

The microstructure and magnetic properties of the Zr-doped α-Fe/Pr2Fe14B nanocomposite magnets prepared by melt-spinning method have been studied by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The magnetization reversal behavior during the recoil processes of nanocomposite alloys has been investigated by analyzing the hysteresis curves and recoil loops of demagnetization curves. An enhanced magnetic properties has been obtained by the addition of 1 at. % Zr in α-Fe/Pr2Fe14B alloys, where the coercivity Hc increases from 470.7 to 793.2 kA/m, the maximum energy product (BH)max from 66.8 to 90.8 kJ/m3, the remanence ratio Mr/Ms from 0.74 to 0.77. The recoil loop results show that the maximum value of the integrated recoil loop area for 1 at. % Zr doped sample is quietly low of 1.87×10-3, only 1/2 for the Zr-free and 1/3 for 5 at. % Zr doped samples respectively. This result indicates that the 1 at. % Zr doped sample has a lower energy loss, resulting from a low recoverable portion of the magnetization remaining as long as the applied reversal field is below the coercivity Hc. This study provides a promising guideline for the future fabrication of low-energy-loss nanocomposite magnets for electric machines and generators.

Effect of Ce doping on the magnetic and magnetocaloric properties of Pr0.5Sr0.5−xCexMnO3 manganites

The magnetic and magnetocaloric effects of manganites of Pr0.5Sr0.5−xCexMnO3 (x = 0, 0.04, 0.08 and 0.1) prepared by standard solid-state reaction method are investigated. Large magnetic entropy changes (ΔSm) with the ferromagnetic–paramagnetic transition have been found. The ΔSm and Curie temperature (TC) gradually increase with increasing Ce content. The maximum of magnetic entropy change in a low magnetic change of 15 kOe is about −1.93 J kg−1 K−1 for x = 0.1 sample with a TC value of 310 K. Due to the large ΔSm and tunable TC around the room temperature, it is suggested that Pr0.5Sr0.5−xCexMnO3 could be used as desirable active room temperature magnetic refrigerants.

Magnetic and Magnetocaloric Properties of Perovskite Pr0.5Sr0.5-xBaxMnO3

This paper studies the effects of A-site substitution by barium on the magnetic and magnetocaloric properties of Pr 0.5 Sr 0.5-x Ba x MnO₃ (x = 0, 0.04, 0.08 and 0.1). The tetragonal crystal structures of the samples are confirmed by room temperature X-ray diffraction. The dependence of the Curie temperature (T C ) and the magnetic entropy change (ΔS M ) on the Ba doping content has been investigated. The samples of all doping contents undergo the second order phase transition. As the concentration of Ba increased, the maximum entropy change (|ΔS M | max ) increased gradually, from 1.15 J kg ?1 K ?1 (x = 0) to 1.36 J kg ?1 K ?1 (x = 0.1), in a magnetic field change of 1.5 T. The measured value of T C is 265 K, 275 K, 260 K and 250 K for x = 0, 0.04, 0.08 and 0.1, respectively. If combining these samples for magnetic refrigeration, the temperature range of ~220 K and 290 K, where |ΔS M |max is stable at ~1.27 J kg ?1 K ?1 and RCP = 88.9 Jㆍg ?1 for ΔH = 1.5 T. Pr 0.5 Sr 0.5-x BaxMnO₃ compounds, are expected to be suitable for magnetic-refrigeration application due to these magnetic properties.

Enhanced magnetic properties in lean rare earth Pr2Fe14B/Fe3B nanocomposite alloys

Abstract The Pr lean Pr2Fe14B/Fe3B nanocomposite alloys were prepared by melt spinning method and subsequent thermal annealing. The effect of annealing temperature on the magnetic properties and the microstructure of these magnets has been investigated. The results show that the optimal magnetic property of Pr2Fe14B/Fe3B nanocomposite alloy with a high coercivity Hc = 211·4 kA m−1, a large remanence Mr = 1·18 T and a large energy product (BH)max = 73·9 kJ m−3 has been obtained by controlling the annealing temperature in the amorphous alloy. The enhanced (BH)max is mainly attributed to the increase in the intergrain exchange coupling effect due to the refined nanocrystal microstructure. This demonstrates that the control of the nanocrystal microstructure in the amorphous alloys plays a significant role for the further improvement of the magnetic properties of these magnets.