Shuiyuan Chen

Large exchange bias field in the Ni–Mn–Sn Heusler alloys with high content of Mn

The exchange bias properties have been investigated in bulk Mn50Ni40−xSn10+x (x=0, 0.5, and 1) Heusler alloys with high content of Mn, in which the largest exchange bias field is up to 910 Oe for Mn50Ni40Sn10 alloy. In these alloys, the excess Mn atoms would occupy not only the Sn sites but also the Ni sites, and the moments of Mn on Sn or Ni sites are coupled antiferromagnetically to those on the regular Mn sites, respectively. The origin of this considerably large exchange bias field has been discussed.

Converse magnetoelectric effect in ferromagnetic shape memory alloy/piezoelectric laminate

In laminates, the converse magnetoelectric (CME) effect is often achieved by an elastic coupling between magnetostrictive and piezoelectric layers. Here the authors report on an alternative mechanism for obtaining CME. In a transition-metals-based ferromagnetic shape memory alloy/piezoelectric ceramic laminated composite, the stress-induced martensitic transformation is utilized to gain the magnetic changes, which gives rise to a giant CME effect consequently. The strong CME is observed at room temperature over a broad bandwidth, under weak magnetic bias and electric field.

Electric field control of magnetism without magnetic bias field in the Ni/Pb(Mg1/3Nb2/3)O3-PbTiO3/Ni composite

This paper reports on the electric field control of magnetism without magnetic bias field in a Ni/Pb(Mg1/3Nb2/3)O3-PbTiO3/Ni composite prepared by electrochemical deposition. The converse magnetoelectric effect, which was measured by an induction method, shows a peak value of 0.45 G/V at the resonance frequency of 102 kHz. Without magnetic bias field, the magnetization of the Ni layers can be controlled by an applied dc electric field in a reversible and reproducible way and shows an analogous on-off behavior with the electric field switching on and off alternatively.

Direct and converse magnetoelectric effects in Ni43Mn41Co5Sn11/Pb(Zr,Ti)O3 laminate

A ferromagnetic shape memory alloy was utilized to construct a Ni43Mn41Co5Sn11/Pb(Zr,Ti)O3 laminate. Large direct and converse magnetoelectric (ME) effects were observed at resonance frequencies around the martensitic transition temperature of Ni43Mn41Co5Sn11 alloy, and the temperature affects the ME properties remarkably. The ME coefficients respond almost linearly to the applied ac electric or magnetic field. The mechanism of both direct and converse ME effects in the laminate is discussed.

Surface and size effects of magnetic properties in ferromagnetic nanoparticles

The oscillatory behavior of the average magnetic moment as a function of the cluster size and shape is studied. Based on Monte Carlo simulation, the temperature dependence of magnetic moment with different cluster size is studied for free and embedded Co clusters. It is found that the oscillations superimposed on the moment decrease are associated with not only the geometrical structure effects but also the thermal fluctuation roles. The fitting results on the temperature dependence of moment for both free and embedded clusters by using Bloch exponent law reveal that differences between them exist. At the same time, the simulated results are compared with the experimental facts.

Non-Volatile Ferroelectric Switching of Ferromagnetic Resonance in NiFe/PLZT Multiferroic Thin Film Heterostructures.

Magnetoelectric effect, arising from the interfacial coupling between magnetic and electrical order parameters, has recently emerged as a robust means to electrically manipulate the magnetic properties in multiferroic heterostructures. Challenge remains as finding an energy efficient way to modify the distinct magnetic states in a reliable, reversible, and non-volatile manner. Here we report ferroelectric switching of ferromagnetic resonance in multiferroic bilayers consisting of ultrathin ferromagnetic NiFe and ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films, where the magnetic anisotropy of NiFe can be electrically modified by low voltages. Ferromagnetic resonance measurements confirm that the interfacial charge-mediated magnetoelectric effect is dominant in NiFe/PLZT heterostructures. Non-volatile modification of ferromagnetic resonance field is demonstrated by applying voltage pulses. The ferroelectric switching of magnetic anisotropy exhibits extensive applications in energy-efficient electronic devices such as magnetoelectric random access memories, magnetic field sensors, and tunable radio frequency (RF)/microwave devices.

Effect of electric field on magneto-transport properties in La2/3(Ca0.6Ba0.4)1/3MnO3/Pb(Zr0.52Ti0.48)O3 laminated composite

The effects of electric field on the magnetization and Hall resistivity were investigated in a laminated composite consisting of polycrystalline perovskite La2/3(Ca0.6Ba0.4)1/3MnO3 (LCBMO) material and Pb(Zr0.52Ti0.48)O3 (PZT) ferroelectric ceramic. Upon applying an electric field (9 kV/cm) on the ferroelectric ceramic, the Hall resistivity change of the LCBMO layer is up to − 23%. The electric field-modulated Hall resistivity in LCBMO/PZT composite is attributed to the coaction of magnetization change and carrier concentration change, which result from stress-induced variation of both metal–insulator transition and ferromagnetic–paramagnetic transition.

Dynamics of Magnetization Reversal in Thin Polycrystalline Co Films

The thin polycrystalline Co films with different annealed time were prepared by magnetron sputtering method. XRD and hysteresis loops of the samples were measured. A mean field equation with Heisenberg model for calculating dynamic scaling was derived. The experimental and simulated results indicate that, the scaling law, A=A0+H0 a ω b, describes well dynamic magnetization along easy and hard axes for the anisotropy magnetic films; the anisotropy scaling exponents exist clearly in the anisotropy films; the simulated results are consistent with the experimental those.

Nonvolatile Modulation Effects of Electric Field on the Magnetic and Electric Properties in La–Ca–MnO 3 /PMN-PT Heterostructures

We demonstrate that ferroelectric (FE) domain switching induces a nonvolatile tuning of the magnetic and electric properties in La_0.6Ca_0.4MnO₃ (LCMO)/Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ heterostructure. The FE domain switching in the substrate contributes to an in-plane strain that changes the spin exchange coupling in the LCMO layer, and therefore results in a nonvolatile magnetization difference of up to -17.5% at zero external magnetic field, as well as a nonvolatile resistance difference of up to 20.3%. This nonvolatility of the modulation effect on the magnetic and electric properties by an electric field demonstrates great potential for the applications of magnetic and electric devices.

Magnetic Properties for Magnetic Quantum Dot Arrays: Fast Fourier Transformation and Micromagnetism Study

Based on the Monte-Carlo simulation and fast Fourier transformation-micro-magnetism (FFTM) method, magnetic properties with different parameters for the 4×4 Magnetic Quantum Dot Arrays (QDA) were studied. The calculating processes show that the same calculated results can be obtained by both methods above. But the FFTM method can save much time in obtaining results, which suggest that the method be employed to study more complex systems. The calculated results indicate that there exists obvious difference in the magnetic hysteresis loops with different temperatures, which can be well explained by considering the relationship between the easy-magnetization axis and the organization anisotropy of the QDA system. Furthermore, saturation field (Hs) increases with the dipolar interaction increasing, which is attributed to the competition between dipolar energy (ED) and Zeeman energy (EZ). The calculated results can fit the experimental results very well. Besides, it is found that the dipolar interaction constant D has a great influence on magnetic properties.