Hijung Kim

Effective spin injection in Au film from Permalloy

The electrical injection of spin current in the lateral Permalloy/Au/Permalloy spin valve devices was investigated. Clear spin valve effects were found in nonlocal spin valve measurements. The spin diffusion length of Au was evaluated to be 168nm. High spin injection polarization of 26% at 15K was achieved from our samples with low interface resistance. The observed spin injection reveals the highest polarization among the reported values. This work demonstrates the high spin injection polarization through clean interface with low interface resistance.

SrFeO3 nanoparticles-dispersed SrMoO4 insulating thin films deposited from Sr2FeMoO6 target in oxygen atmosphere

Dielectric SrMoO4 thin films were deposited from Sr2FeMoO6 target in oxygen atmosphere, showing obvious M–H hysteresis loops at room temperature. It was revealed by transmission electron microscopy that SrFeO3 nanoparticles are dispersed in the SrMoO4 grains, to which the hystersis loops of the thin films are ascribed. This SrMoO4 thin film can be useful as a barrier material for Sr2FeMoO6-based devices, owing to easy fabrication process and compatibility with Sr2FeMoO6. Magnetic SrFeO3 nanoparticles are expected to enhance tunneling magnetoresistance.

Microstructure and magnetoresistance of sputtered bismuth thin films upon annealing

We investigated the microstructure and magnetotransport properties of sputtered Bi upon annealing. The grain size and the orientation of polycrystalline Bi thin films can be manipulated through a proper annealing treatment. Weak-oriented fine grains, of which size is about 0.1μm, were found in as-sputtered Bi films. Careful annealing at 270°C results not only in a grain growth of up to 1.1μm but also in a [001]-preferred orientation structure. The grain size increases exponentially with annealing time in the temperature range of 266–270°C. The grain-growth exponent (n) and the activation energy (Q) were evaluated to be 0.32±0.05 and 70.7kJ∕mol, respectively. The magnetoresistance (MR) of Bi films is strongly dependent on the microstructure and thickness of the film, and on the measured temperature. A very high MR of 30,000% can be observed in the annealed 7-μm-thick Bi films when measured at low temperature (4K). The drastic increase in MR after annealing is largely attributed to the trigonal-axis-oriente...

Structure and magneto-optical properties of fine-grain garnet thin films

Abstract The structure and magneto-optical properties of fine-grain garnet thin films crystallized by the rapid recurrent thermal annealing (RRTA) method have been studied. The RRAT method has been used to crystallize BiGaDyIG garnet single-layer or BiGaDyIG/AI double-layer films and to get nanometer grain size (about 30–50 nm), which results in a large Faraday rotation angle, a smoother surface and fewer voids in the films. Meanwhile we have discovered that the Faraday rotation angle increases with the number of recurrences during the rapid annealing and quenching. With the more recurrent annealing one can not only get a strong Faraday effect, but it suppresses the appearance of DyFeO 3 phase in garnet films, which has been explained very well. By applying the new method, the as-deposited films have been succesfully crystallized to the (BiDy) 3 (FeGa) 5 O 12 garnet phase. They exhibited excellent magneto-optical properties with a coercivity of about 1500 Oe and effective Faraday rotation angle of 1.5°. The composition, magnetic and magneto-optical properties of the crystallized garnet films have been examined.

Observation of Spin-Orbit Interaction Parameter Over a Wide Temperature Range Using Potentiometric Measurement

Spin-orbit interaction parameter (¿) can be obtained by measuring the Shubnikov-de Haas oscillation, but this method is valid at only very low temperature. The current induced spin polarization in a 2-D electron gas layer is measured by potentiometric geometry which measures spin dependent chemical potential shifts. Subsequently, a spin-orbit interaction parameter can be extracted up to T = 250 K. In an inverted In_0.52Al_0.48As/In_0.53Ga_0.47As/In_0.52Al_0.48As quantum well system, a of 5.65 × 10^-12 eVm and 3.85 × 10^-12 eVm are obtained at T = 1.8 and 250 K, respectively.

Two magnetic phases in the co-sputtered Fe-Si/sub 3/N/sub 4/ thin film

The structure and magnetic properties of Fe-Si/sub 3/N/sub 4/ thin films fabricated by a co-sputtering technique were studied by X-ray diffractometry and magnetometry. With increasing area fraction of Si/sub 3/N/sub 4/ pieces on the Fe target, magnetization of the films decreased due to reduced Fe content and reduced grain size of the bcc crystalline phase. The temperature dependence and field dependence of magnetization of co-sputtered thin films can be explained by a mixture of two types of particles showing paramagnetism and ferromagnetism.

Detection of Rashba field using a rotational applied field

The intrinsic Rashba field in an InAs quantum well is observed using a potentiometric geometry in which a circular shaped permalloy electrode is utilized with a rotational applied field. From the ratio of the curve shift to the applied field and the amplitude of potentiometric signal, a Rashba field of 8.84 T can be estimated. This method is a very simple and accurate alternative to quantitatively observe the Rashba field.

A new measurement system for magnetic anisotropy with pulsed rotation field

A novel approach for the measurement of magnetic anisotropy is introduced, and a preliminary small-scale system is described. In order to create a rotating magnetic field without mechanical rotation of the electromagnet, two pairs of electromagnets are placed so that their axes are mutually perpendicular. One of the pairs of electromagnets is excited with a sinusoidal current and the other with a cosine current. Thus, the net magnetic field vector rotates. The exciting currents are intermitted by a zero crossing analog switch to minimize power loss in the electromagnets and power supplies. The rotating magnetic field generates a torque on the magnetically anisotropic sample placed in the center of the field. The torque is measured with a piezoelectric sensor. In a preliminary experiment, a rotating field intensity of 0.2 T was obtained with a 1-kg electromagnet and a 20-W power amplifier. The calibration for the measurement was carried out with pure nickel wire. The anisotropy constants of several amorphous ribbons were measured. >

Spin transfer enhancement and switching behavior in exchange bias spin valves

Spin transfer from polarized conduction electrons to the free layers magnetic moment is considerably enhanced when the fixed layer of a spin valve is magnetically pinned by an exchange bias antiferromagnet. This enhancement leads to significantly lower threshold current densities for spin transfer magnetization switching and to much higher total current induced effective fields. The phase diagram is not symmetric as in non-exchange biased spin valves but asymmetric over the field axis.

The low temperature dependence of magnetization of as-deposited Fe-Hf-C-N nanocrystalline thin films

Abstract We have studied the magnetic properties of as-deposited Fe-Hf-C-N and Fe-Hf-N nanocrystalline thin films with good soft magnetic properties. Thin films have been prepared by a reactive magnetron sputtering method in a nitrogen atmosphere. The as-deposited thin films are fully nanocrystallized during deposition by controlling the composition and sputtering condition. Fe-Hf-C-N and Fe-Hf-N films show good soft magnetic properties of saturation magnetization of about 17 kG and coercivity of 0.5 Oe. In order to investigate the intrinsic magnetic properties, we analyzed the temperature dependence of magnetization. Both of the thin films are composed of finely dispersed Fe(~ 5 nm) and smaller Hf precipitates. It seems that exceptionally small grains and precipitates enhance the soft magnetic properties.