Huiyuan Sun

Magnetic properties and microstructures of FePt∕Ti bilayer films sputter deposited onto glass amorphous substrates

FePt∕Ti granular films were fabricated onto glass amorphous substrates using a dc facing-target magnetron sputtering system at various Ti underlayer thickness, then annealed at temperature Ta ranging from 200 to 700°C. In the FePt(30nm)∕Ti(1nm) film annealed at 600°C, the coercivity about 12kOe is obtained. The results of x-ray diffraction indicate that a ternary FePtTi alloy is formed. Thus, the formation of the ternary FePtTi alloy is considered to play an important role in magnetic properties.

Magnetic characterization of diluted magnetic semiconductor thin films

In studies of weak magnetism in diluted magnetic semiconductor thin films, there is often a significant difficulty in subtracting the background signal arising from the substrate. In the present work, an improved magnetic correction method is proposed. For Al doped ZnO and Fe doped TiO2 films, the magnetic moment and coercivity of the samples were corrected by the improved method, and the maximum fitting error due to the glass substrate was calculated. The accuracy and rationale of the improved method are discussed and compared with the traditional method. The results show that room temperature ferromagnetism is observed in Fe doped TiO2 thin films. The ferromagnetism is strongly correlated with the substitution of Ti by Fe in the TiO2 lattice, which results in a change in the crystal structure and the quality of the crystallization of the TiO2 films. The changes are responsible for altering ferromagnetism in the films.

Optical and magnetic properties of porous anodic alumina/Ni nanocomposite films

A simple method to tune the optical properties of porous anodic alumina (PAA) films embedded with Ni is reported. The films display highly saturated colors after being synthesized by an ac electrodeposition method. The optical properties of the samples can be effectively tuned by varying the oxidation time of aluminum. The ultrashort Ni nanowires (100 nm long and 50 nm in diameter) present only fcc phase and show no apparent averaged effective magnetic anisotropy. The coercivity mechanism of the Ni nanowires in our case is consistent with fanning mechanism based on a chain-of-spheres model. PAA/Ni films with structural color and magnetic properties have friability-resistant feature and can be used in many areas, including decoration, display, and multifunctional anti-counterfeiting technology.

Optical and magnetic properties of PAA@Fe nanocomposite films

A simple method to fabricate porous anodic alumina films embedded with Fe is reported. The films exhibit vivid structural colors and magnetic properties after being synthesized by an ac electrodeposition method. The optical properties of the samples can be effectively tuned by varying the oxidation time of aluminum. The coercivity mechanism of the Fe nanowires in our case is consistent with fanning reversal mode. PAA@Fe films can be used in many areas including decoration, display and multifunctional anti-counterfeiting applications.

The annihilation of vertical-Bloch lines in the walls of hard domains to which bias fields and in-plane fields are alternately applied ☆

Abstract The annihilation of vertical-Bloch lines in magnetic domain walls of the ordinary hard bubbles, to which both bias fields and in-plane fields are alternately applied, is investigated experimentally. The influence of an in-plane magnetic field on ordinary hard bubbles (OHB), dumbbell domains of the first kind (ID), and dumbbell domains of the second kind (IID) was analyzed, and a critical in-plane field range [ H ip 0 , H ip 2 ] for vertical Bloch line (VBL) annihilation was found. For the three types of hard domains ( H ip 0 is the minimum critical in-plane field of VBLs which begin to be unstable, H ip 2 is the minimum critical in-plane field which only needs to be applied one time for collapse of all OHBs), the critical field range is the same with H ip 0 ≐8 πM s . We hypothesize that there exists a direction along which the vertical-Bloch lines in the domain walls are annihilated most easily. It is also observed that the stability of vertical-Bloch lines in the domain walls does not depend on the initial state. This provides a more detailed description of the minimum critical in-plane field than previously known.

Microstructure and magnetic properties of Ti/CoCrPt/Ti pseudo-sandwich nanogranular films

We prepared Ti/CoCrPt/Ti pseudo-sandwich granular films by radio-frequency and dc magnetron sputtering onto glass substrates and subsequent in situ annealing. We investigated the microstructure and magnetic properties of the films as a function of Ti overlayer thickness (x). X-ray diffraction profiles show that the CoCrPt magnetic layers are formed as the hexagonal close-packed (HCP) structure. Vibrating sample magnetometer measurements indicate that the out-of-plane coercivity reaches the maximum 1675.5 Oe when x=5 nm. Atomic force microscopy images show the minimum average grain size D=7.2 nm and the average roughness R/sub a/=1.0 nm. Magnetic force microscopy images show that the minimum average magnetic cluster size is about 6.4 nm at x=5 nm.

Influence of temperature on vertical Bloch lines in the domain walls of three kinds of hard domains

The temperature stability of vertical Bloch lines in the domain walls of three kinds of hard domains in uncompressed states is investigated experimentally. It is found that there exist three critical temperature ranges in which vertical Bloch lines are unstable for each kind of hard domain, i.e., [T01,(T0)OHB] for ordinary hard bubbles (OHBs), [T01,(T0)ID] for the first kind of dumbbells (IDs), and [T01,(T0)IID] for the second kind of dumbbells (IIDs). Here T01 is the initial critical temperatures in which vertical Bloch lines, in the walls of ordinary hard bubbles, the first kind of dumbbells and the second kind of dumbbells, are annihilated, while (T0)OHB, (T0)ID, and (T0)IID are the final critical temperatures at which vertical Bloch lines in their corresponding hard domains annihilate completely.

The annihilation of VBLs in the walls of second kind of dumbbell domains to which bias fields and in-plane fields are alternately applied

Abstract The annihilation of vertical Bloch lines in magnetic domain walls of the second kind of dumbbell domains, to which both bias fields and in-plane fields are alternately applied, are investigated experimentally. A critical in-plane field range [Hip(0), Hip′] is found. We hypothesize that there exists a direction along which the vertical Bloch lines in the domain walls annihilate most easily. It is observed that the annihilation of vertical Bloch lines in the domain walls does not depend on the initial state. This provides a more detailed description of the minimum critical in-plane field than obviously known.

Analysis of the domain wall structures of the three kinds of hard domains in garnet bubble films

It was found experimentally that dumbbell domains of the second kind produced at high temperature can convert to dumbbell domains of the first kind at low temperature. And the ordinary hard bubbles produced at low temperature can convert to dumbbell domains of the first kind at high temperature. So we conclude that the domain wall structures of the three kinds of hard domains are the same. We also observe that the equilibrium separation between two neighboring vertical-Bloch lines is widened with the increasing temperature when the hard domains collapse under the effect of bias field.

Electric field control of magnetization in Cu2O/porous anodic alumina hybrid structures at room temperature

Cu2O nanoporous films are deposited on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. This paper focuses on voltage driven magnetization switching in Cu2O/PAA (CP) composite films prepared by DC-reactive magnetron sputtering. By applying a dc electric field, the magnetization of the CP composite films can be controlled in a reversible and reproducible way and shows an analogous on-off behavior. The magnitude of the change in the magnetization was about 75 emu/cm3 as the electric field was switched on and off. Resistive switching behavior was also observed in as-prepared CP composite films. Further analysis indicated that the formation/rupture of conducting filaments composed of oxygen vacancies is likely responsible for the changes in the magnetization as well as in the resistivity. Such reversible change of magnetization controlled by an electric field at room temperature may have applications in spintronics and power efficient data storage technologies.