Variation of the saturation magnetization through a neon implanted YIG film

The saturation magnetization of a YIG film implanted with 5*10¹⁴ neon ions/cm² at an energy of 450 keV was studied. By removing very thin layers from the ion implanted part of the film the magnetization was found to change. As a result of the analysis of these changes in the saturation magnetization it was possible to establish a profile for the magnetization as a function of depth through the ion implanted part of the film. The profile is asymmetric and shows a decrease in the magnetization of up to 35 % of the initial value at a depth coinciding with the depth of maximum strain.     

Structural and magnetic properties of Co-C composite films and Co/C multilayer films

CoC composite films and Co/C multilayer films have been prepared by a method incorporating ion beam sputtering and plasma chemical vapor deposition. It has been found that the structure and magnetic properties of both the Co-C composite and the Co/C multilayer films depend strongly on the substrate temperature during deposition. The Co-C composite film deposited at room temperature is amorphous, with relatively low saturation magnetization and coercivity. On the other hand, the film deposited at 250 °C is composed of fine Co crystallites separated by amorphous C or Co-C phase. As a result, both the saturation magnetization and coercivity are increased compared with the film deposited at room temperature. When deposited at room temperature, the Co/C multilayer film exhibits good periodicity, with a period of 70 nm (Co: 40 nm, C: 30 nm) and sharp and flat Co-C interfaces. High magnetization (602 emu/cm³) and low coercivity (1.6 Oe) are obtained for such a film. However, increasing the substrate temperature to 250 °C was found to be detrimental to the magnetic properties due to the formation of cobalt carbide at the Co-C interface. Received: 11 July 2000 / Accepted: 13 July 2000 / Published online: 30 November 2000     

Studies of the magnetic and reversal properties for thin CoCrTa films

The effects of magnetic layer thickness on film structural and magnetic properties were studied systematically with emphasis on the thermal effects on thin recording media films. X-ray diffraction measurements reveal structural changes as thickness decreases, and the existence of a “Cr enriched phase” associated with the interface. The saturation magnetization M_s decreases with thickness and the thickness of the “dead layer” was found to be ∼23 Å. Systematic measurements of effective anisotropy, coercivity and saturation magnetization as functions of temperature have been carried out. Magnetic viscosity measurements reveal that thermal stability is affected not only by grain sizes but also by anisotropy reduction associated with nanostructure evolution, as the film thickness decreases.     

Magnetic properties of ultrathin Ni films

The magnetic properties of Au/Ni/Si(100) films with Ni thicknesses of 8–200 Å are studied at T=77 K using a scanning magnetic microscope with a thin-film high-temperature dc SQUID. It is found that the Ni films, with an area of 0.6×0.6 mm, which are thicker than 26 Å have a single-domain structure with the magnetic moment oriented in the plane of the film and a saturation magnetization close to 0.17 MA/m. For films less than 26 Å thick, the magnetization of the film is found to drop sharply.     

Microscopic field in nanocrystalline ferromagnetic metal films and the opportunity for studying it by the μSR method

The relation of the microscopic (local) field in nanocrystalline ferromagnetic metal films to macroscopic characteristics (the external magnetic field, average magnetization, saturation magnetization) is determined for the case where a nanocrystalline ferromagnetic film consists of crystallographically ordered grains separated by disordered regions and where the dimensions of grains along a normal to the film plane are much smaller than those in the film plane. In the case of a strong external field (? ? M), the magnetization direction is determined in grains in the form of oblate ellipsoids for metals with uniaxial or cubic magnetocrystalline anisotropy. Expressions are derived for the spin polarization of an ensemble of rapidly diffusing and nondiffusing muons in nanocrystalline ferromagnetic films. It is shown that experiments with “slow” positive muons make it possible to measure all parameters of such structures and to obtain important information for studying phase transition physics.     

Pinning of vortices by the domain structure in a two-layered type II superconductor-ferromagnet system

The effectiveness of magnetic pinning of vortices in a layered system formed by a uniaxial ferromagnet and type II superconductor is considered. It is shown that, irrespective of the saturation magnetization of the ferromagnet, the energy of pinning at the domain structure does not exceed, in order of magnitude, the energy of artificial pinning at a column-type defect. The limitation of pinning energy is caused by the interaction of external vortices with a spontaneous vortex lattice formed in the superconducting film when the magnetization of the ferromagnetic film exceeds the critical value.     

Optimization of MO Bragg diffraction of guided optical waves by MSW in YIG films by using inclined magnetic bias field

We describe a new scheme of noncollinear interaction geometry for magneto-optical (MO) Bragg cells based on inelastic scattering of guided optical wave beams by magnetostatic waves in yttrium–iron–garnet (YIG) films. A great increase of the diffracted light intensity was obtained when using an inclined magnetization of the film, in the case when static in-plane magnetization component is directed along the light propagation direction. It is shown that the diffraction efficiency can be increased more than two times, at a specific value of the angle (≈35°) between the saturation magnetization vector and the normal to the film surface. The effect can be explained through a four-wave model of the diffraction process, which can take place in optical waveguides with MO gyrotropy. The results obtained by a simple analytical solution of the diffraction problem are found to be in good qualitative agreement with the experimental observations.     

Impact of magnetic surface anisotropy on the precessional switching of magnetization in Pt-alloy nanofilms

Precessional switching of magnetization in CoPt and FePt nanofilms is investigated by solving the Landau–Lifshitz–Gilbert (LLG) equation analytically and numerically. Switching in these films occurs only above a critical value of the magnetic field, and it further depends on the magnetocrystalline anisotropy and saturation magnetization of the film. The presence of magnetic surface anisotropy in these films reduces the switching time significantly. Also, the switching time in the case of Pt-alloys of Co and Fe is low compared to that in the case of pure Co and Fe films.     

Microstructure and magnetic properties of Ni-rich Ni54Mn25.7Ga20.3 ferromagnetic shape memory alloy thin film

A Ni₅₄Mn_25.7Ga_20.3 ferromagnetic shape memory alloy thin film has been fabricated by using the RF magnetron-sputtering technique. The structure and magnetic properties of the film were systematically investigated. The results show that the film is in ferromagnetic martensite state at room temperature with the Curie temperature (T_c) of about 370 K. The saturation magnetization (M_s) of the film reaches 45 emu/g at 300 K, which is about 80% as large as that of Ni–Mn–Ga bulk material. The magnetization hysteresis loops significantly depend on temperatures. The residual magnetization (M_r) and the coercive force (H_c) increase with decreasing temperatures. The grains homogeneously distribute in the film. The microstructure of the film consists of martensite plates. The interface between the martensite variants is clear and straight, indicating a good mobility.     

Linear micromagnetics in thin films: I. Basic equations in the case of in-plane and of perpendicular uniaxial anisotropies

Within the framework of a linearized micromagnetic approach we calculate the formal solutions of the basic equations describing the position dependence of the vector of magnetization in a thin magnetic film. Thereby various cases of mutual orientation of the easy axis of the uniaxial anisotropy, of the external field and of the plane of the film are considered including the situation where the magnetization is perpendicular to the plane of the film. As the origin of local deviations of the direction of magnetization from its mean direction (magnetization ripple) we assume not only random fluctuations of the anisotropy but also a position dependence of the saturation magnetization and of the exchange energy. The stochastic fluctuations of these parameters are known to be closely related to the defect structure of the magnetic material. Furthermore, we derive the relation between correlation functions of the defect structure and the resulting magnetization correlations. This relation serves as the starting point for a full discussion of the statistical properties of the ripple. In part II of this paper we shall give such a discussion in detail for the case of polycrystalline films.     

Magnetic properties of magnetite thin films close to the Verwey transition

Temperature dependence of the magnetic properties of magnetite thin film across the Verwey transition has been investigated. As the temperature is decreased, the magnetization of the film in a fixed field showed a sharp decrease close to the Verwey transition temperature (T_v). The M–H loops of the film have been recorded at various temperatures below and above T_v. It is found that film does not saturate at any temperature and saturation becomes more difficult below T_v. While cooling through T_v, the extrapolated value of magnetization to infinite field (Q), calculated from the numerical fit 4πM=Q [1−(H*/H)^1/2], does not show a drop, but the coefficient indicating difficulty in saturation (H*) shows a sharp rise as does the coercivity.     

Magnetic proximity effect in EuO-Cs interface

In the surface of the ferromagnetic insulator EuO is covered with a small amount of cesium, the photoelectric magnetization curves P(H) show magnetic saturation in contrast to those of the pure surface. The proximity of the Cs film causes the paramagnetism of the clean EuO surface to disappear.     

Temperature dependence of the saturation magnetization of ion-implanted YIG films

The temperature dependence of the saturation magnetization of a series of ionimplanted YIG films is presented. The films were implanted with neon ions at an energy of 450 keV; the dose ranged from 2 to 5*10¹⁴ ions/cm². The experimental data can be described by the molecular field theory showing that the ion-implanted part of the film can be approximated as consisting of two regions each having their own magnetization and Curie temperature. The values of these magnetic parameters vary as a function of dose and differ strongly from the values for pure YIG.     

Effect of a planar magnetic field on the domain wall dynamics in a double-layer uniaxial magnetic film

Motion of an isolated domain wall in a double-layer uniaxial magnetic film, where the film layers differ in characteristic length, saturation magnetization and damping parameter, is investigated by solving the Slonczewski equation. A planar magnetic field is applied normal to the domain-wall plane. The dependences of the threshold field and limiting velocity of disruption of the steady-state motion of the domain wall on the planar magnetic field value are obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 60–63, December, 2008.     

CoPt–Al 2 O 3 Nanocomposite Films: Synthesis,Structure, and Magnetic Properties

The structure and magnetic properties of CoPt–Al2O3 nanocomposite films synthesized by the annealing of Al/(Co3O4 + Pt) bilayers on a MgO(001) substrate at 650°C in vacuum are investigated. The synthesized composite films contain ferromagnetic CoPt grains with an average size of 25–45 nm enclosed in a nonconducting Al2O3 matrix. The saturation magnetization (Ms ~ 330 G) and coercivity (Hc ≈ 6 kOe) of the films are measured in the film plane and perpendicular to it. The obtained films are characterized by a spatial rotational magnetic anisotropy, which makes it possible to arbitrarily set the easy magnetization axis in the film plane or perpendicular to it using a magnetic field stronger than the coercivity (H > Hc).     

Hydrogen-induced changes of the structural and magnetic properties of cerium/iron multilayers

Multilayers of Ce and Fe show a low Curie temperature and saturation magnetization below a critical thickness of the individual Fe layers where amorphous growth occurs. We have studied on a series of such multilayers with different modulation lengths prepared by ion-beam sputtering the impact of hydrogen absorption on their magnetic properties. Hydrogenation was performed during film growth either reactively by introducing hydrogen gas into the UHV chamber or by irradiation with a beam of low-energy hydrogen ions. Hydrogen is absorbed only in the Ce layers, with a concentration near CeH₂. For suitable modulation lengths, the Curie temperature and saturation magnetization are considerably enhanced with respect to the non-hydrided multilayers. This is correlated with the changes in structure and the quality of the interfaces induced by hydrogenation: the irradiation process itself reduces the critical thickness for amorphous growth of Fe, and the chemical interaction of hydrogen causes a considerable sharpening of the interfaces.     

Saturation magnetization of MnBi films with different thicknesses and composition

The saturation magnetization of MnBi films in the low-temperature phase and the quenched high-temperature phase was measured at room temperature by a new method recently described. The measurements were performed with samples of varying thickness and composition (ratio Mn:Bi). The results obtained show no dependence either on film thickness or on composition. Hence, the different magnetization values given in the literature for bulk and thin film samples of the quenched high-temperature phase must not be attributed to a thickness dependence of the samples or to stoichiometric variations. This work has been supported by the data processing program of the Federal Department of Research and Technology of the FRG. The authors alone are responsible for the contents.     

The role of nucleation field of media in heat-assisted magnetic probe recording

We characterize a method of heat-assisted magnetic probe recording on perpendicular media. Heating source is field emission current from a scanning tunneling microscope (STM) tip. Recording media are three kinds of magnetic films, Co/Pt, CoNi/Pt, and Co/Pd multilayers with different nucleation fields. Pulses with amplitude of 5 V were applied between the STM tip and the recording medium. Experiments show that magnetic marks with an average size of 180 nm were formed on both Co/Pt and CoNi/Pt films whose nucleation fields are greater than their saturation magnetization. No marks were observed on the Co/Pd film whose nucleation field is smaller than its saturation magnetization. A model is built to simulate the dynamic process of domain formation in probe-based magnetic recording system. Simulation results agree with experiments and it explains the effect of the nucleation field of medium in perpendicular recording.     

溶胶-凝胶法制备Ni_xZn_(1-x)S薄膜的磁性分析

由于离子掺杂可有效改善ZnS薄膜的特性,故本研究以溶胶-凝胶法制备Ni_xZn_(1-x)S薄膜(x=0.00, 0.05, 0.10, 0.15),并利用XRD、PL光谱及磁性测试仪分析Ni掺杂对其磁性的影响.研究结果表明Ni掺杂量x为0.00、0.05、0.10及0.15时薄膜的饱和磁化强度随分别为6.59×10~(-6) emu/cm~3、4.61×10~(-6) emu/cm~3、3.88×10~(-6) emu/cm~3及3.52×10~(-6) emu/cm~3,即饱和磁化强度随x增加而减小. PL分析表明缺陷发光强度随x增加而减弱,能隙发光强度则随之增强,结合束缚极化子理论便知饱和磁化强度会随x增加而减小. XRD分析表示结晶品质随x增加而变好,说明薄膜中的缺陷数量会随x增加而减少,使得磁信号无法通过缺陷方式传导而导致其磁性减弱.     

Electrical properties of epitaxial magnesium-manganese-zinc ferrite films

The resistivity of Mg-Mn-Zn ferrite films from 2.4 to 12 μ thick was studied as a function of the temperature during cyclic heating from 20 to 450 °C and subsequent cooling. The resistivity and activation energy were found as functions of the film thickness. A study was made of the effect of annealing in air on the resistivity, activation energy, exchange-interaction parameter, saturation magnetization, and domain structure of the Mg-Mn-Zn ferrite films.