X. Q. Zheng

Magnetocaloric effects in RNiIn (R = Gd-Er) intermetallic compounds

Magnetic properties and magnetocaloric effects (MCEs) of the intermetallic RNiIn (R = Gd-Er) compounds have been investigated in detail. GdNiIn and ErNiIn compounds exhibit a ferromagnetic (FM) to paramagnetic (PM) transition around the respective Curie temperatures. However, it is found that RNiIn with R = Tb, Dy, and Ho undergo two successive magnetic phase transitions with increasing temperature. In addition, a field-induced metamagnetic transition from antiferromagnetic (AFM) to FM states is observed in RNiIn with R = Tb and Dy below their respective AFM-FM transition temperatures (Tt). The maximal values of magnetic entropy change (ΔSM) of HoNiIn are –9.5 J/kg K at Tt = 7 K and –21.7 J/kg K at TC = 20 K for a magnetic field change of 5 T, respectively. These two successive ΔSM peaks overlap partly, giving rise to a high value of refrigerant capacity (RC = 341 J/kg at 5 T) over a wide temperature span. It is noted that the RC value of GdNiIn is as high as 326 J/kg due to the relatively broad distribut...

Large refrigerant capacity of RGa (R = Tb and Dy) compounds

The magnetic properties and magnetocaloric effects (MCEs) of RGa (R = Tb and Dy) compounds are investigated. The TbGa compound exhibits two successive magnetic transitions: spin-reorientation (SR) transition at TSR = 31 K and second-order ferromagnetic (FM)–paramagnetic (PM) transition at Curie temperature TC = 154 K, while the DyGa compound undergoes a SR transition with TSR=25 K and a FM–PM transition with TC = 113 K. It is noteworthy that a broad distribution of the magnetic entropy change peak is observed. The values of the refrigerant capacity (RC) for TbGa and DyGa are found to be 620.6 and 381.9 J/kg for a field change of 0–5 T, respectively. And for a field change of 0–7 T, the values are 900 and 584.2 J/kg, respectively. The large value of RC for TbGa and DyGa originates from the combined contribution from SR and FM–PM transitions, which enlarges the temperature span of large MCE.

Giant magnetocaloric effect in Ho12Co7 compound

Magnetic properties and magnetocaloric effects of Ho12Co7 compound are investigated by magnetization and heat capacity measurement. The Ho12Co7 compound undergoes antiferromagnetic (AFM)-AFM transition at T1 = 9 K, AFM-ferromagnetic (FM) transition at T2 = 17 K, and FM-paramagnetic transition at TC = 30 K, with temperature increasing. There are two peaks on the magnetic entropy change (ΔSM) versus temperature curves and the maximal value of –ΔSM is found to be 19.2 J/kg K with the refrigerant capacity value of 554.4 J/kg under a field change from 0 to 5 T. The shape of the ΔSM-T curves obtained from heat capacity measurement is in accordance with that from magnetization measurement. The excellent magnetocaloric performance indicates the applicability of Ho12Co7 as an appropriate candidate for magnetic refrigerant in low temperature ranges.Magnetic properties and magnetocaloric effects of Ho12Co7 compound are investigated by magnetization and heat capacity measurement. The Ho12Co7 compound undergoes antiferromagnetic (AFM)-AFM transition at T1 = 9 K, AFM-ferromagnetic (FM) transition at T2 = 17 K, and FM-paramagnetic transition at TC = 30 K, with temperature increasing. There are two peaks on the magnetic entropy change (ΔSM) versus temperature curves and the maximal value of –ΔSM is found to be 19.2 J/kg K with the refrigerant capacity value of 554.4 J/kg under a field change from 0 to 5 T. The shape of the ΔSM-T curves obtained from heat capacity measurement is in accordance with that from magnetization measurement. The excellent magnetocaloric performance indicates the applicability of Ho12Co7 as an appropriate candidate for magnetic refrigerant in low temperature ranges.

Large magnetoresistance and metamagnetic transition in PrGa

The magnetic phase transition and the magnetoresistance (MR) in bulk intermetallic PrGa compound are investigated experimentally. Two successive magnetic transitions, ferromagnetic (FM)-antiferromagnetic (AFM) transition and AFM-paramagnetic transition, are observed at T1 = 28 K and T2 = 36 K, respectively. It is found that the PrGa compound exhibits a field-induced metamagnetic transition from AFM to FM state and a considerable change in lattice constants in a temperature range of 28-36 K. Accompanied with the AFM-FM transition, a negative MR occurs, and the maximal MR values are ∼30% and ∼34% at 28 K under the fields of 1 T and 5 T, respectively.

Textured PrCo5 nanoflakes with large coercivity prepared by low power surfactant-assisted ball milling

The effect of the milling time on the structure, morphology, coercivity, and remanence ratio of textured PrCo5 nanoflakes produced by low power surfactant-assisted ball milling (SABM) was investigated. The X-ray powder diffraction (XRD) patterns indicate that the SABM PrCo5 samples are all CaCu5-type hexagonal structure. The average grain size is smaller than 10 nm when the SABM time is equal to or longer than 5.5 h. The thickness of nanoflakes is mainly in the range of 50−100 nm while the length is 0.5−5 μm when the SABM time reaches 8 h. For the field-aligned PrCo5 nanoflakes, the out-of-plane texture is indicated from the increasing (0 0 l) peaks in the XRD patterns, and the easy magnetization direction is perpendicular to the flake surface. The strong texture of PrCo5 nanoflakes leads to a large coercivity Hc (7.8 kOe) and obvious anisotropic magnetic behaviors for the aligned samples.

Textured Pr2Fe14B flakes with submicron or nanosize thickness prepared by surfactant-assisted ball milling

The textured Pr2Fe14B nanoflakes were produced by surfactant-assisted ball milling (SABM). Single phase tetragonal structure was characterized for the samples before and after SABM by X-ray diffraction (XRD). The thickness and length of the as-milled flakes are mainly in the range of 50–150 nm and 0.5–2 μm, respectively. For the field-aligned Pr2Fe14B nanoflakes, the out-of-plane texture (the easy magnetization direction (EMD) along the c-axis) is indicated from the increasing (00l) peaks in the XRD patterns. SEM image demonstrates that the EMD is parallel to flaky surface, which is different from the RCo5 (R = rare earth) system with EMD perpendicular to the surface. We propose a hypothesis that the easy glide planes are related with the area of crystal planes. In addition, a large coercivity Hc = 3.9 kOe is observed in the Pr2Fe14B flakes with strong texture.

Structure and magnetic properties of low-temperature phase Mn-Bi nanosheets with ultra-high coercivity and significant anisotropy

The microstructure, crystal structure, and magnetic properties of low-temperature phase (LTP) Mn-Bi nanosheets, prepared by surfactant assistant high-energy ball milling (SA-HEBM) with oleylamine and oleic acid as the surfactant, were examined with scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the coercivity of LTP Mn-Bi nanosheets was systematically investigated. Results show that the high energy ball milling time from tens of minutes to several hours results in the coercivity increase of Mn-Bi powders and peak values of 14.3 kOe around 10 h. LTP Mn-Bi nanosheets are characterized by an average thickness of tens of nanometers, an average diameter of ∼1.5 μm, and possess a relatively large aspect ratio, an ultra-high room temperature coercivity of 22.3 kOe, a significant geometrical and magnetic anisotropy, and a strong (00l) crystal texture. Magnetization and demagnetization behaviors reveal that wall pinning is the domina...

Evolution of magnetic properties and magnetocaloric effect in TmNi1-xCuxAl (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) compounds

The magnetic and magnetocaloric properties of TmNi1-xCuxAl (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) compounds have been investigated. With the substitution of Ni by Cu, the Tm-magnetic moment rotates its direction from basal plane to the c-axis and finally becomes canted antiferromagnetism structure with larger projected moments along the c-axis near Tord. Furthermore, large reversible magnetocaloric effects have been observed in TmNi1-xCuxAl compounds around Tord, with no thermal hysteresis and magnetic hysteresis loss. The values of −ΔSMmax and refrigerant capacity are greatly improved when the part of Ni was superseded by Cu. In particular, under the magnetic field change of 2 T, a large −ΔSMmax of TmNi0.7Cu0.3Al (10.7 J/kg K) is almost twice that of TmNiAl (5.5 J/kg K) and 17.2 J/kg K for TmCuAl around 4 K. The present results indicate that TmNi1-xCuxAl (x ≥ 0.3) compounds could be considered as good candidate materials for low-temperature and low-field magnetic refrigerant.