V.N. Lepalovskij

Magnetic Properties and Giant Magnetoimpedance of FeNi-Based Nanostructured Multilayers With Variable Thickness of the Central Cu Lead

The magnetoimpedance effect is attractive for thin film-based magnetic sensor applications. Recently a significant progress has been made in the development of appropriate theories, preparation and characterization of MI thin film-based structures. In the present work FeNi(100 nm)/Cu(3.2 nm)]4/FeNi(100 nm)/Cu(LCu)/[FeNi(100 nm)/Cu(3.2 nm)]4/FeNi(100 nm) multilayered structures with open magnetic flux have been prepared by RF-sputtering. Their magnetic properties and MI were studied as a function of the thickness of the central Cu lead. It was shown that the thickness of the Cu lead is an important parameter. The highest sensitivity (≈ 50%/Oe, f=160 MHz) was observed for the sample with a central Cu layer thickness of about a half-thickness of a magnetic layer (LCu ≈ 250 nm). The maximum sensitivity of the real part of the impedance was also obtained for this thickness (≈ 75%/Oe).

Fe20Ni80/Fe50Mn50 film magnetoresistive medium

The influence of several physico-technological factors on the microstructure and the magnetic and magnetoresistive properties of film structures based on Fe20Ni80/Fe50Mn50 bilayers with exchange (magnetic) bias is investigated. The dependences of the magnetic bias, coercive force, and anisotropic magnetoresistance on the deposition sequence and thickness of layers in the structures, substrate temperature, annealing temperature, and measurement temperature are determined for films obtained by magnetron sputtering, including with a high-frequency electric bias applied to the substrate. It is shown that the film SiO2/Ta(5)/Fe20Ni80(5)/Fe50Mn50(20)/Fe20Ni80(40)/Ta(5) structure offers an optimal combination of properties as a magnetoresistive medium with internal magnetic bias. Testing data for magnetic sensors made of this material by optical lithography are presented.

Tailoring the Exchange Bias in FeNi/FeMn Bilayers by Heat Treatment and FeMn Surface Oxidation

The FeNi(30 nm)/FeMn(20 nm) bilayers were deposited by magnetron sputtering at room temperature onto glass substrates in a magnetic field. Afterward, they were subjected to heat treatments at temperatures from 50 °C to 400 °C in vacuum or in a gas mixture containing oxygen. The as-deposited FeNi/FeMn bilayers presented an exchange bias field Hex = 30 Oe, a coercivity Hc ≈ 3 Oe, and a blocking temperature Tb ≈ 140 °C. An increase of the annealing temperature results in a monotonous decrease of Hex for temperatures up to 200 °C. For higher annealing temperatures, Hex remains almost constant. Hc sharply increases in the range from 200 °C to 300 °C, and finally decreases dramatically upon annealing>300 °C. Preferential surface oxidation of Mn during heat treatment in a gas mixture results in the formation of the ferromagnetic α-Fe(Mn) phase and leads to the change of the magnetic moment of the samples. The adjustment of temperature and annealing time in a gas mixture allows us to increase the switching field value of exchange biased FeNi/FeMn bilayers.

Effect of phase separation in an Fe20Ni80/Fe50Mn50 structure with exchange coupling

The effect of heat treatment and partial oxidation of an Fe50Mn50 layer on the structure and magnetic properties of exchange-coupled Fe20Ni80/Fe50Mn50 layers has been investigated. The behavior of the exchange-bias field and coercive force depending on the temperature of annealing upon heat treatment in a vacuum or in an oxygen-containing gas mixture has been studied. It has been shown that, by adjusting the parameters of annealing in the gas mixture, it is possible to increase the field of switching of the exchange-coupled Fe20Ni80/Fe50Mn50 layers.

Nanostructured Magnetoimpedance Multilayers with Different Thickness of FeNi Components

Magnetic properties and magnetoimpedance of [FeNi/Cu]n/FeNi/Cu (500 nm)/[FeNi/Cu]m/FeNi MI asymmetric and symmetric structures were studied for multilayeres with different thickness (25, 50 or 170 nm) of permalloy layers. The asymmetric structures in the case of FeNi layers of 50 nm show higher sensitivities comparing with symmetric structures. Asymmetric multilayered structures with 25 nm thick FeNi layers are an interesting subject for further investigation as the interactions between FeNi layers seem to be providing the best MI response.

Surface Modification of Thin Iron Films in Aromatic Solvents at Ambient Conditions

Recently we reported interesting phenomenon resulting in formation of irregular polycyclic structures on the surface of Fe or Ni nanoparticles immersed in toluene at ambient conditions. The objectives of the present work were to test the possibility of ambient deposition of carbon on the surface of Fe film, to study the kinetics of the deposition and to characterize the structure of the deposits. Periodic structural and magnetic measurements were performed on the dry samples just taken out of toluene. We observed that carboneous layers on the Fe surface are formed rather fast – they can be initially detected after about one week treatment.

Effect of temperature on magnetization reversal characteristics of ferromagnetic 3d metal layers within exchange-coupled FeMn-based structures

Multilayer films Fe20Ni80/FeMn/FM (with FM = Ni, Fe11Ni89, Fe20Ni80, Co30Ni70, Fe, Co) have been prepared and their structure has been estimated. Their hysteretic properties and interlayer coupling parameters have been studied in a temperature range of 5–350 K. Regularities of the magnetization reversal of ferromagnetic layers under magnetic exchange-bias conditions have been interpreted.

Peculiarities of the Giant Magnetoimpedance in Permalloy-Based Film Structures in the Important Temperature Range for Practical Applications

Multilayer structures based on Fe19Ni81 films have been obtained by ion-plasma sputtering and investigated on an impedance spectroscopy apparatus equipped with a temperature unit. An increase in the magnetoimpedance ratios for the total impedance and its real part has been found for the multilayer structure (Cu/FeNi)5/Cu/(Cu/FeNi)5 upon heating from 25 to 50°C. The maximum of the giant magnetoimpedance ratio of the total impedance ΔZ/Z = 56% has been observed at a frequency of 80 MHz with a sensitivity of 18%/Oe, while the maximum of the real part ΔR/R = 170% was observed at the frequency of 10 MHz with the sensitivity of 46%/Oe. Magnetization and resistivity at the direct current have been found to depend insignificantly on the temperature and, hence, the relaxation mechanism due to the magnetoelastic anisotropy was proposed as the most probable mechanism of increasing the value and sensitivity of the magnetoimpedance effect.

Antidot patterned single and bilayer thin films based on ferrimagnetic Tb-Co alloys with tailored magnetic anisotropy

Introduction of periodically arranged nanoscale holes is an effective way of tuning the magnetic anisotropy and coercivity of magnetic films [1].

Using magnetoresistive films with unidirectional anisotropy to register elastic deformations

The magnetoresistive properties of FeMn/Fe10Ni90 films with unidirectional anisotropy have been studied under controlled elastic deformation. It has been shown that linear strain or compression significantly affects the magnetic anisotropy of the films and, as a consequence, leads to major changes in magnetoresistance curves. The dependences of the magnetoresistance on the relative deformation have been determined for varied external magnetic field, magnetic biasing, film thickness, and sample geometry. An optimum combination of the listed parameters has been found that corresponds to the maximum sensitivity and nearly anhysteretic type of the tensomagnetoresistive effect.