Basic Magnetic Characteristics Research Articles

표면 자기광 커 효과의 이해

지난 20여년간 표면자성 현상의 연구에 가장 도움이 많이 되었던 실험방법중 하나인 표면 자기광 커효과(Surface magneto-optic Kerr effect, SMOKE) 실험 방법을 소개하고자 한다. 예를 들어 단일층의 철막이 강자성이 되는지, 또 큐리(Curie)온도는 bulk와 비교하여 얼마나 떨어져 있는지, 자화 용이축(easy-axis)은 어느 방향인지 등 매우 기본적인 자성박막의 특성은 스핀트로닉스(spintronics) 분야의 연구에 가장 기본적인 정보이다. 표면 자기광 커 효과(SMOKE)는 이러한 물음에 대한 답을 줄 수 있는 매우 효율적인 방법이다. We will introduce the surface magneto-optic Kerr effect (SMOKE), which is one of the most helpful experimental methods in the area of surface magnetism for the last two decades. The basic magnetic characteristics of magnetic thin film is the most essential part for the further understanding and application. For example, the possibility of the realization of ferromagnetism for a single layer of iron, its Curie temperature far below that of bulk iron, and the direction of easy axis are the fundamental questions for the spintronic application. SMOKE is an efficient method to answer for the questions above.

ChemInform Abstract: ε‐Fe2O3: An Advanced Nanomaterial Exhibiting Giant Coercive Field, Millimeter‐Wave Ferromagnetic Resonance, and Magnetoelectric Coupling

AbstractReview: 104 refs.

ε-Fe2O3: An Advanced Nanomaterial Exhibiting Giant Coercive Field, Millimeter-Wave Ferromagnetic Resonance, and Magnetoelectric Coupling

Nanosized iron oxides still attract significant attention within the scientific community, because of their application-promising properties. Among them, e-Fe2O3 constitutes a remarkable phase, taking pride in a giant coercive field at room temperature, significant ferromagnetic resonance, and coupled magnetoelectric features that are not observed in any other simple metal oxide phase. In this work, we review basic structural and magnetic characteristics of this extraordinary nanomaterial with an emphasis on questionable and unresolved issues raised during its intense research in the past years. We show how a combination of various experimental techniques brings essential and valuable information, with regard to understanding the physicochemical properties of the e-polymorph of Fe2O3, which remained unexplored for a long period of time. In addition, we recapitulate a series of synthetic routes that lead to the formation of e-Fe2O3, highlighting their advantages and drawbacks. We also demonstrate how magne...

Magnetic and Cytotoxicity Properties of La1−xSr x MnO3(0 ≤ x ≤ 0.5) Nanoparticles Prepared by a Simple Thermal Hydro-Decomposition

This study reports the magnetic and cytotoxicity properties of magnetic nanoparticles of La1−xSrxMnO3(LSMO) withx = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 by a simple thermal decomposition method by using acetate salts of La, Sr, and Mn as starting materials in aqueous solution. To obtain the LSMO nanoparticles, thermal decomposition of the precursor was carried out at the temperatures of 600, 700, 800, and 900 °C for 6 h. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM, and SEM. Structural characterization shows that the prepared particles consist of two phases of LaMnO3(LMO) and LSMO with crystallite sizes ranging from 20 nm to 87 nm. All the prepared samples have a perovskite structure with transformation from cubic to rhombohedral at thermal decomposition temperature higher than 900 °C in LSMO samples ofx ≤ 0.3. Basic magnetic characteristics such as saturated magnetization (MS) and coercive field (HC) were evaluated by vibrating sample magnetometry at room temperature (20 °C). The samples show paramagnetic behavior for all the samples withx = 0 or LMO, and a superparamagnetic behavior for the other samples havingMSvalues of ~20–47 emu/g and theHCvalues of ~10–40 Oe, depending on the crystallite size and thermal decomposition temperature. Cytotoxicity of the synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result shows that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extract of LSMO nanoparticles.

A simple thermal decomposition synthesis, magnetic properties, and cytotoxicity of La0.7Sr0.3MnO3 nanoparticles

This study reports the new and simple synthesis of magnetic La0.7Sr0.3MnO3 (LSMO) nanoparticles by thermal decomposition method using acetate salts of La, Sr and Mn as starting materials. To obtain the LSMO nanoparticles, thermal decomposition of the precursor is carried out at the temperatures of 600, 700, 800, 900, and 1000°C for 6 hours. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM and SEM. Structural characterization shows that the prepared particles consisted of two phases of LaMnO3 (LMO) and LSMO with crystallite sizes ranging from 18 to 55 nm. All the prepared samples have a perovskite structure which changes from cubic to rhombohedral with the increase in the thermal decomposition temperature. Basic magnetic characteristics such as saturation magnetization (M S) and coercive field (H C) are evaluated by sample vibrating magnetometry at room temperature (20°C). The samples show soft ferromagnetic behavior with M S values of ∼9–55 emu/g and H C values of ∼8–37 Oe, depending on the crystallite size and thermal decomposition temperature. The relationship between the crystallite size and the magnetic properties is presented and discussed. The cytotoxicity of synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result showed that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extraction of LSMO nanoparticles.

Magnetic properties and structural parameters of nanosized oxide ferrimagnet powders produced by mechanochemical synthesis from salt solutions

The phase composition, the structural parameters, and the basic magnetic characteristics of a number of nanosized powders of simple spinel ferrites produced by the method of mechanochemical reactions from salt systems were studied. The influence of size and surface effects on the saturation magnetization and magnetic anisotropy was determined. The applicability of the shell model to the description of the magnetic properties of nanosized spinel ferrites is discussed.

Preparation, structure and properties of La0.67Pb0.33(Mn1-xCox)O3-δ

La0.67Pb0.33(Mn1-xCox)O3-δ ceramics with x=0, 0.01, 0.03, 0.06, 0.1 and 0.15 have been prepared in a two-step procedure. Precursor gels were made by the wet chemical malic acid method. The gels were calcined and then converted into ceramics by heat treatment at 950 °C and 1000 °C in air. X-ray diffraction showed that the compounds were phase pure. The crystal structure symmetry of the compounds was confirmed to be rhombohedral (space group R3c) for the whole investigated range of x. All compounds undergo a paramagnetic–ferromagnetic phase transition between 335 K and 225 K. The basic magnetic characteristics such as the Curie temperature \(\mathit{T}_{\mathrm{C}}\), the paramagnetic Curie temperature θ, the effective magnetic moment \(\mathit{\mu}_{\mathrm{eff}}\) and the saturated magnetization \(\mathit{\mu}_{\mathrm{s}}\) decrease with increasing Co doping. The ferromagnetic transition is accompanied by an anomaly in the electrical resistance for all compounds. The high-temperature insulator–metal transitions (\(\mathit{T}_{\mathrm{p}}\)) do not coincide with the relevant \(\mathit{T}_{\mathrm{C}}\). A large magnetoresistance peak of about 15% was observed for all compounds at \(\mathit{T}_{\mathrm{C}}\).

Theory of ferromagnetic (III,Mn)V semiconductors

The body of research on (III,Mn)V diluted magnetic semiconductors initiated during the 1990's has concentrated on three major fronts: i) the microscopic origins and fundamental physics of the ferromagnetism that occurs in these systems, ii) the materials science of growth and defects and iii) the development of spintronic devices with new functionalities. This article reviews the current status of the field, concentrating on the first two, more mature research directions. From the fundamental point of view, (Ga,Mn)As and several other (III,Mn)V DMSs are now regarded as textbook examples of a rare class of robust ferromagnets with dilute magnetic moments coupled by delocalized charge carriers. Both local moments and itinerant holes are provided by Mn, which makes the systems particularly favorable for realizing this unusual ordered state. Advances in growth and post-growth treatment techniques have played a central role in the field, often pushing the limits of dilute Mn moment densities and the uniformity and purity of materials far beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds, material quality and magnetic properties are intimately connected. In the review we focus on the theoretical understanding of the origins of ferromagnetism and basic structural, magnetic, magneto-transport, and magneto-optical characteristics of simple (III,Mn)V epilayers, with the main emphasis on (Ga,Mn)As. The conclusions we arrive at are based on an extensive literature covering results of complementary ab initio and effective Hamiltonian computational techniques, and on comparisons between theory and experiment.

Fe3C nanopowder synthesized by laser pyrolysis and its annealing behaviour

AbstractWe describe the Fe3C‐based nanopowder obtained through the laser‐induced pyrolysis of the gas mixture of Fe(CO)5 and C2H4. This ferromagnetic nanopowder was characterized by XRD, HRTEM and magnetic measurements. Aggregated core‐shell nanoparticles were identified in the nanopowder; Fe3C cores were coated with pyrolytic carbon. The mean coherence domain size estimated by the Scherrer formula was 18 nm. Basic magnetic characteristics were measured at 20 °C: HC = 42.0 kA m−1; σR = 31.2 A m2 kg−1; σS = 95.7 A m2 kg−1 (at 1200 kA m−1). The Curie temperature TC was 227 °C. Thermally induced phase transformations are discussed. Copyright © 2006 John Wiley & Sons, Ltd.

Magnetism of cigarette ashes

Mineral composition of cigarette ashes is well studied in the literature, but no reports are available about the magnetic fraction. Our study presents an investigation of the basic magnetic characteristics of ashes from several commercially available cigarette brands and a wood ash. Magnetic susceptibility, which is a concentration-dependent parameter in case of uniform mineralogy, shows that cigarette ashes contain relatively high amount of magnetic iron minerals, similar to that in wood ash from our study and other literature data. Magnetization data suggest that cigarette ashes contain some 0.1 wt% or lower quantity of magnetite, depending on the brand. Analyses of magnetic mineralogy imply that the main magnetic minerals in ashes from higher quality cigarette brands are magnetite and iron carbide cementite, while in ashes from lower quality brands without additives magnetic minerals are pure and substituted with foreign ions magnetite. Magnetic grain-size analysis shows that cigarette ashes contain significant amount of very fine, nano-meter sized magnetic particles, as well as coarser (up to several microns), magnetically stable grains. Thus, the magnetic study of cigarette ashes proved that these plant ashes possess non-negligible magnetic properties. The results could serve for better elucidation of mineralogy of cigarette ashes as a whole, as well as for future investigation on the presence of magnetic ultra fine particles in cigarette smoke, which may be inhaled in lungs during smoking.

Study on Manufacture of 2:17 Sm-Co Magnets by Powder Injection Molding

Manufacture of 2:17 Sm-Co magnets by powder injection molding was investigated. The binder of thermoplastic polymer was selected as the wax-based system including paraffin wax, stearic acid and high density polyethylene. Before mixing with paraffin wax and high density polyethylene, the powder of 5-8 µm was coated by stearic acid. The molding compacts were obtained under 200°C without deficits. Solvent debinding and thermal debinding were combined to remove the binder. The basic magnetic characteristics of the specimen were of the same level as those by powder metallurgy technique, which indicated that to fabricate 2:17 Sm-Co magnets by powder injection molding was feasible.

Temperature dependence of magnetic properties in Fe-Co and Fe-Cr base nanocrystalline alloys

The temperature dependence of the magnetic properties (i.e., ac magnetic permeability and magnetoimpedance voltage) is analyzed for Fe-Co and Fe-Cr base nanocrystalline materials. Around the Curie point of the residual amorphous matrix a magnetic transition is detected, associated with the magnetic decoupling of ferromagnetic crystallites. The magnetic nature of such magnetic transition is analyzed within the framework of the random anisotropy model, taking into account the basic structural and magnetic characteristics of the constituent magnetic phases.

Special Features of the Divertor Region in the Magnetic Field of the l =2 Yamator

The structure of edge magnetic field lines of the l =2 Yamator (the region outside closed magnetic surfaces) is numerically analysed. Yamator is a new stellarator-type magnetic system, where a significant magnetic well can be formed at moderate values of basic magnetic surface characteristics. In comparison with a straight classical stellarator or a torsatron, this system has a double number of separatrix ribs (or so-called "X-points"). The present investigations give a general idea about the behavior of the edge magnetic field lines in the l =2 Yamator and give grounds to discuss a feasible concept of the divertor.

Preparation and characterization of glass covered magnetic wires

The amorphous glass covered magnetic wires (AGCW) are of great interest due to their specific magnetic properties that can be controlled through the composition as well as through the metallic core diameter and the thickness of the glass cover. The specific magnetic properties are determined by the magnitude of the magnetic anisotropies induced by the mechanical stresses due to the preparation process. This paper presents a series of conditions that are determinant for the preparation process of the AGCW. The basic magnetic characteristics of the highly positive, negative and nearly zero magnetostrictive AGCW are presented as a function of composition and samples state. Recently performed FMR measurements showed that the metal–glass interface influences the magnetic characteristics including the magnetic anisotropy. The magnetic domain structure of the highly positive AGCW presents a single domain axially magnetized with some closure domains at the ends of the wire while for the wires obtained after the glass removal it presents an axially magnetized inner core with a typical maze domain configuration at the surface of the wire.

Induction Pulse of Compound Magnetic Wires by the Large Barkhausen Jump

The compound magnetic sensors using twisted vicalloy and permalloy wire were composed and their basic characteristics were investigated. This compound magnetic wire could generate a pulse voltage with high S/N even when flux change was extremely slow. This type of magnetic sensor seems to be applicable for magnetic recording head when they are prepared as thin film device. Before applying to recording head, the basic magnetic characteristics of these wires and their pulse induction phenomena caused by large Barkhausen jump were precisely investigated and their induction principle was compared with that on Wiegand wire.

A multipurpose magnetometer for measuring basic magnetic characteristics with a newly designed capacitive torque sensor

An economic and versatile magnetometer for measuring basic magnetic characteristics such as hysteresis loops, magnetic anisotropy and magnetostriction with a single system was built. It is based on the principle that most magnetic characteristics could be obtained by analyzing the torque acting on a sample under an appropriate magnetic field. A capacitive torque sensor with 0.1 nJ resolution measures such torque. By limiting the duration of electromagnetic excitation only to the measuring period (about 4 s), temperature rise of the magnet becomes negligible so that a very compact and economic electromagnet and power supply (10 kg weight, 25 mm air gap, 350 W power consumption, and 480 kA/m of generated field) is realized.

Radial density profiles in a poloidal divertor modelled by diffusion across a region with variable connection length

AbstractA simple model to describe the diffusion of particles in the scrape‐off layer of a poloidal divertor tokamak is presented. This model takes into account the basic magnetic characteristics of an open poloidal divertor and provides analytical expressions for the plasma density profiles at the divertor target, that are used to fit the experimental measurements in JET.

Micromagnetic analysis of a coupled thin-film self-biased magnetoresistive sensor

A theoretical micromagnetic study of the basic magnetic and performance characteristics of an unshielded dual coupled thin-film self-biased magnetoresistive sensor is presented. The usual sense current flowing in the Permalloy magnetoresistor (MR) provides a magnetizing field for a strongly coupled magnetically soft adjacent layer (SAL) whose resulting demagnetization field acts as a bias source for the MR. The analysis methods presented provide quick, accurate, and numerically well-conditioned solutions of the relevant micromagnetic equations. Results presented include the self-biasing capability of the MR-SAL sensor as a function of sensor height, the MR-SAL thickness ratio, and sense current density, as well as device performance (output amplitude, second harmonic, and phase distortion) as a function of element height and record density. Theoretical results computed via the present method are compared with experimentally measured quantities as well as results (neglecting exchange) obtained via two-dimensional boundary integral methods. A brief comparison of the SAL and permanent magnet bias techniques for the MR sensor is also included.

Magnetic properties of superlattices formed from ferromagnetic and antiferromagnetic materials.

We present theoretical studies of basic magnetic response characteristics of superlattice structures formed from alternating layers of ferromagnetic and antiferromagnetic materials, each described through use of a localized spin model. The geometry explored here is one in which the antiferromagnet consists of sheets parallel to each interface within which the spins are aligned ferromagnetically. The study of the classical (mean-field) ground state as a function of magnetic field shows that a sequence of spin-reorientation transitions occur, particularly for superlattices within which the antiferromagnetic constituent consists of an even number of layers. For the various phases, we present calculations of the spin-wave spectrum, and also the infrared absorption spectrum.

On some magnetic characteristics of a system of lithium ferrites for microwave applications

The purpose of the present work is to study the influence of Mn, Zn and Bi on the basic magnetic characteristics 4π M s, Δ H, tg δ μ and T c of the system Li 0.5(1+ y) Zn 0.5 x+ity Mn z Fe2.5(1-0.4 x-0.6 y-0.4 z-ϵ)O 4, where the values of the parameters vary in the limits O≤ x≤0.5, 0.1≤ y≤0.3, 0.03≤ z≤0.05.