D. Y. Shin

Precise Investigation of Domain Pinning Energy in GaMnAs Using Planar Hall Effect and Magnetoresistance Measurements

The planar Hall effect (PHE) and magnetoresistance (MR) measurements have been carried out on a GaMnAs ferromagnetic semiconductor. The PHE and MR spectra exhibit interesting two-step magnetization switching behavior arising from the magnetic anisotropy properties of the system. By fitting the angle-dependent planar Hall resistance (PHR) data taken at 5 kG with the Stoner-Wohlfarth model, the cubic and uniaxial anisotropy constants were independently obtained. The anisotropy constants lead to the precise determination of easy axis direction, which turns out to be in good agreement with the easy axis determined from the angular plot of the switching field. The domain pinning energies were further obtained by fitting the angle dependence of the switching field, including the effect of uniaxial anisotropy

Distribution of magnetic domain pinning fields in Ga 1 − x Mn x As ferromagnetic films

Using the angular dependence of the planar Hall effect in GaMnAs ferromagnetic films, we were able to determine the distribution of magnetic domain pinning fields in this material. Interestingly, there is a major difference between the pinning field distribution in as-grown and in annealed films, the former showing a strikingly narrower distribution than the latter. This conspicuous difference can be attributed to the degree of non-uniformity of magnetic anisotropy in both types of films. This finding provides a better understanding of the magnetic domain landscape in GaMnAs that has been the subject of intense debate.

Tunable quaternary states in ferromagnetic semiconductor GaMnAs single layer for memory devices

The authors show that staggered asymmetric planar Hall resistance (PHR) loops observed in GaMnAs ferromagnetic semiconductor films with biaxial in-plane magnetic anisotropy result in four stable resistance states at zero magnetic field owing to the formation of a stable multidomain structure during magnetization reversal. The values of PHR can be systematically controlled by changing the direction and the scanning range of the applied magnetic field. The possibility of a quaternary memory device based on the observed four PHR states is demonstrated by obtaining consistent results in the writing process using appropriate sequences of magnetic field pulses.

Single and multidomain characteristics of GaMnAs investigated by magnetotransport measurements

We have investigated the magnetization reorientation process of GaMnAs ferromagnetic films by changing external field direction in planar Hall effect (PHE) measurement. While the angular dependences of PHE data taken with clockwise and counterclockwise under strong magnetic field (i.e., above 400Oe) are completely overlapped without hysteresis, they are significantly different under small magnetic field (i.e., below 50Oe) by exhibiting nonabrupt hysteresis. We have analyzed such angular dependence of PHE using the magnetic free energy based on Stoner-Wohlfarth model. The behavior observed under the high field was well understood in terms of coherent rotation of magnetization in the form of single domain. However, the nonabrupt hysteric behavior observed with low field cannot be explained by a single domain picture and requires involvement of multidomain structures.

Growth of Polycrystalline Cd0.8Zn0.2Te Thick Films for X‐Ray Detectors

Cd 1-x Zn x Te is known as promising medical X-ray detector material but CdZnTe as a single crystal is not available in large sizes. As an alternative to single crystal, CdZnTe thick film was grown by vacuum thermal evaporator to 100 μm thickness. The characteristics of thick films were analyzed by XRD, EDS, SEM and current-voltage measurements. Zn composition is x = 0.2 and resistivity is higher than 10 9 Ω cm.

Effect of shape anisotropy on the magnetization reversal process of (Ga,Mn)As ferromagnetic semiconductors

We have carried out the planar Hall effect measurement on two different sizes of Hall bar devices fabricated from GaMnAs ferromagnetic films. The detailed information on the magnetic anisotropy properties including the shape anisotropy field were obtained from the angular dependence of planar Hall resistance. The shape anisotropy field per magnetization in the device with 10μm channel width was about 39G. Though the value of shape anisotropy is small, it affects the magnetization reversal processes of the 10μm Hall device by showing steplike feature in the angular dependence of switching fields.

Four states memory function in GaMnAs ferromagenic semiconductor epilayer

GaMnAs ferromagnetic semiconductor has strong biaxial in-plane anisotropy, which generates four stable magnetization easy axes at zero magnetic field. This feature results in double switching behavior in the main loop of planar Hall resistance (PHR) spectrum. The minor loops of PHV spectrum exhibited four stable states corresponding to four magnetic easy axes at zero magnetic field. This feature clearly demonstrates the possibility of quaternary memory device application using GaMnAs ferromagnetic semiconductor.