J. C. Zhang

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 (xu2009=u20091–4) 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 80u2009kOe. In addition, an enhanced magnetostrain (0.28%) at 110u2009K associated with the phase transition in Ni50Mn33Fe4In13 was observed after the martensitic phase transformation induced by demagnetization at 100u2009K. 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.

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 (xu2009=u20090, 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 (xu2009=u20090 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 1.5u2009K/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.

Effects of Ca substitution on the magnetic properties in La1-xCaxMn0.90Cu0.10O3 (x=0.05–0.30) manganites

Systematic AC and DC magnetic measurements were carried out to investigate the magnetic properties of La1-xCaxMn0.90Cu0.10O3 (x=0.05–0.30) system. A striking paramagnetism (PM) to ferromagnetism (FM) transition is observed at the FM ordering temperature TC. Below TC, the samples with x≤.0.20 show a visible unexpected drop in zero-field cooled (ZFC) DC magnetization curves near 100 K, which is believed to be associated with the domain wall pinning effects. As for the sample with x=0.30, there is no anomalous behavior near 100 K, while another different magnetic phase transition is shown up below 50 K in both FC and ZFC curves. Detailed experimental results show that the phenomenon is resulted from the phase competition rather than solely magnetic interactions.

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.

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 123 – Anisotropic transport and magnetic properties of Pr1/2Sr1/2MnO3 single crystal sample

Publisher SummaryrnThis chapter reports evident anisotropy of transport and magnetic properties for Pr1/2Sr1/2MnO3 single crystal. Resistivity and magnetization for Pr1/2Sr1/2MnO3 single crystal samples are measured in the directions of parallel and perpendicular to the ferromagnetic (FM) plane. The observed anisotropic transport and magnetic properties in antiferromagnetic (AFM) and FM states can be explained by the double exchange model with dx2-y2 orbital structure: with the anisotropic orbital structure, carriers in the FM state or AFM state move only in the FM layers and show two-dimensional metallic behavior. As the A-type AFM state undergoes a transition to a canted spin state below TN, it also shows spin-flop transition at T<TN. In such a classical DE model the presence of spin-canted phase is predicted, which is consistent with the magnetization results. Within the ferromagnetic layers in the A-type AFM structure, one can expect that the DE mechanism is in effect, and that it enhances the conductivity within the FM layers. In addition, the crystal structure of the A-type system favors the dx2-y2 orbits, giving rise to two-dimensional band for the eg electrons. Thus, it can be expected the two-dimensional anisotropic transport and magnetic properties for the A-type AFM structure.