S.X. Cao

Martensitic phase transition, inverse magnetocaloric effect, and magnetostrain in Ni50Mn37-xFexIn13 Heusler alloys

In this paper, we have performed the martensitic phase transition, inverse magnetocaloric effect, and magnetostrain in Ni50Mn37-xFexIn13 (x = 1–4) Heusler alloys. Experimental results indicate that the martensitic phase transition temperature in these materials decreases dramatically with increasing Fe substitution for Mn, which can be explained by the hybridization between Ni and Mn atoms. Large magnetic entropy for Ni50Mn35Fe2In13 could be achieved above room temperature under the applied magnetic field up to 80 kOe. In addition, an enhanced magnetostrain (0.28%) at 110 K associated with the phase transition in Ni50Mn33Fe4In13 was observed after the martensitic phase transformation induced by demagnetization at 100 K. The reason for the enhanced strain has been discussed in detail.

A considerable metamagnetic shape memory effect without any prestrain in Ni46Cu4Mn38Sn12 Heusler alloy

Spontaneous strains during martensitic transformation and magnetic-field-induced transformation have been systemically studied for Ni46Cu4Mn38Sn12 Heusler alloy, respectively. A large spontaneous strain with the value of about 0.12% upon martensitic transformation has been observed in this alloy, which is almost three times larger than that in ternary Ni–Mn–Sn alloy. In addition, such a value of strain can be obtained through a fully reverse martensitic transformation induced by a field of about 45 kOe, exhibiting a considerable metamagnetic shape memory effect without any prestrain. This behavior can be attributed to magnetoelastic coupling between stable martensite and metastable fraction of austenite.

Ferromagnetic resonance investigation in as-prepared NiFe/FeMn/NiFe trilayer

NiFe/FeMn/NiFe trilayer prepared by dc magnetron sputtering was systematically investigated by ferromagnetic resonance technique (FMR) at room temperature. For NiFe/FeMn/NiFe trilayer, there are two distinct resonance peaks both in in-plane and out-of-plane FMR spectra, which are attributed to the two NiFe layers, respectively. The isotropic in-plane resonance field shift is negative for the bottom NiFe layer, while positive for the top NiFe layer. And, such phenomena result from the negative interfacial perpendicular anisotropy at the bottom NiFe/FeMn interface and positive interfacial perpendicular anisotropy at the top FeMn/NiFe interface. The linewidth of the bottom NiFe layer is larger than that of the top NiFe layer, which might be related to the greater exchange coupling at the bottom NiFe/FeMn interface.

A large and reproducible metamagnetic shape memory effect in polycrystalline Ni45Co5Mn37In13 Heusler alloy

We present a detailed study of strain behavior associated with martensitic transition in polycrystalline Ni45Co5Mn37In13 Heusler alloy. A spontaneous phase transition strain with the value of about 0.4% in this alloy can be acquired by applying and removing magnetic field, exhibiting a large two-way metamagnetic shape memory effect (MSME) with nonprestrain. This effect is originated from magnetoelastic coupling due to a large difference in Zeeman energy between austenitic and martensitic phases. In addition, it was also found that even after three magnetic field cycles at 320 K, the two-way MSME is still reproducible. Such characteristic could be ascribed to a random orientation of martensite variants in present alloy.

Tuning martensitic transformation and large magnetoresistance in Ni50−xCuxMn38Sn12 Heusler alloys

In this paper, polycrystalline Ni50−xCuxMn38Sn12 alloys (x = 0, 2, 4, 6) were prepared. The influence of Cu doping on the martensitic transformation and magnetic properties were investigated in these alloys. Experimental results indicate that the martensitic transformation temperature decreases and the Curie temperature increases with the increasing of substitution of Cu for Ni. Therefore, the magnetic properties in both austenitic and martensitic phases could be tuned by Cu content in these alloys. In addition, magnetoresistance were also performed and discussed in detail. A large magnetoresistance (up to 39%) was obtained by the magnetic field induced reverse martensitic transformation.

Complex ferromagnetic-antiferromagnetic phase transition and glass-like arrest of kinetics in Sm1−xBaxCrO3 (x = 0 and 0.1)

The dc magnetization studies of polycrystalline sample Sm1−xBaxCrO3 (x = 0 and 0.1) show the existence of a magnetic glass-like arrest of kinetics. There exist constant frozen fractions of antiferromagnetic state in this complex phase transition process, the frozen fractions are about 33% and 17%, respectively, in SmCrO3 and Sm0.9Ba0.1CrO3 at the cooling and warming rates of 1.5 K/min. The degree of ferromagnetic-antiferromagnetic (FM-AFM) phase transitions is closely corresponding to the kinetic behaviors and thermomagnetic irreversibility. The FM-AFM phase transition and the frozen AFM fractions jointly affect the kinetics of glassy behaviors. The magnetic phase transition and glassy state was gradually repressed with the increase of the applied magnetic field, this complex behavior could be tuned in a number of ways in a two parameter (T and H) phase space.

Exchange Bias Properties in Bulk Ni45Co5Mn38Sn12 Heusler Alloy

We report the exchange bias properties in the bulk Ni45Co5Mn38Sn12 quaternary Heusler alloy. The ferromagnetic (FM) –antiferromagnetic (AFM) interactions get reinforced after the Co substitution for Ni in the Ni-Mn-Sn alloy, which increase the exchange bias field (HE). A maximum shift in hysteresis loops of 306 Oe was observed in the 10 kOe field cooled sample. The origin of this large exchange bias field has been discussed. Magnetic hysteresis loop obtained in the zero field cooled (ZFC) mode shows double-shifted loop, and the reason of this phenomenon has been explained in detail.

Martensitic Transformation and Metamagnetic Shape Memory Effect in Ni46Co4Mn37in13 Heusler Alloy

The phase transition strain and magnetostrain during the martensitic transformation have been systematically investigated in Ni46Co4Mn37In13 Heusler alloy. A large phase transition strain with the value of about 0.25% upon martensitic transition has been observed, which is much larger than that in other metamagnetic shape memory alloys. In addition, such phase transition strain can be also obtained by the field change of about 50 kOe, exhibiting a large metamagnetic shape memory effect with nonprestrain. This behavior can be attributed to magnetoelastic coupling, which is caused by large difference in Zeeman energy between austenitic and martensitic phases.

Step and Domain Boundary Effect of Surface Reconstruction to Si(111)-√ 3×√3-Ag

The influence of step and domain boundary on growth of Si(111)-√ 3×√3-Ag has been studied in situ using optical surface second-harmonic generation and low energy electron diffraction. The second harmonic intensity shows a difference of about 50% for Si(111) surfaces with different miscut angles and domain boundary densities, although no significant difference has been observed in low energy electron diffraction patterns, indicating a significant impediment to the growth of Si(111)-√ 3×√3-Ag by step and domain boundaries. Simulation results reveal a 90% coverage of Si(111)-√ 3×√3-Ag on the vicinal substrate with an miscut angle of 0.41o, consistent with the dynamics of Ag atoms on Si(111)-7×7 surface. The influence of two dimentional adatom gas on surface structure has also been discussed.

Chapter 122 – The reentrant behaviour of spin-glass phase in (La,Pr)0.5Ca0.5MnO3 manganites

This chapter presents resistivity, magnetic susceptibility, and magnetization data for La 0.5 Ca 0.5 MnO 3 and Pr 0.5 Ca 0.5 MnO 3 compounds. Reentrant spin-glass phase behavior is reported for La 0.5 Ca 0.5 MnO 3 and Pr 0.5 Ca 0.5 MnO 3 . ac susceptibility curve for both compounds is very similar and a cusp appears at ∼40K after Tc. The p(T) measured in a field of 8 T appears M-I transition, but at lower temperature, the resistivity becomes an insulator again. The M(H) gives the presence of FM clusters in the La 0.5 Ca 0.5 MnO 3. For La 0.5 Ca 0.5 MnO 3 compounds, it has been shown that CO occurs not only in AFM regions but can also occur in FM regions (COFM). On the other hand, accumulating theoretical and experimental evidence indicates the importance of the phase separation (PS), which shows the coexistence of the submicrometer CO and FMM phase. The competition between the coexisting phases opens the possibility for the appearance of locally metastable states. Data indicate that both Pr 0.5 Ca 0.5 MnO 3 and La 0.5 Ca 0.5 MnO 3 compounds have the same ground state, which shows the existence of some FM clusters in the background of remaining region in a spin frozen state.