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The results of the study on the magnetic properties of Fe Ti B O nanocrystalline films, subjected to annealing in vacuum at 200, 300, and 400 C, are presented. Films with a mixed (nanocrystalline amorphous) structure, 0.52 m thick, were obtained by magnetron deposition on glass substrates. Hysteresis loops were measured using a vibrating magnetometer, and the field and spectral dependences of the transverse Kerr effect (TKE) were determined. Magnetization reversal processes were visualized using a magneto-optical Kerr magnetometer. It was shown that the processes of partial crystallization of the initially amorphous phase and the redistribution of Ti and B within crystalline grains and grain boundaries, leading to the formation of new phases as a result of annealing, manifest themselves in a two-stage magnetization reversal process and in the modification of the TKE spectra. [ABSTRACT FROM AUTHOR]

Composite films of (Cd As ) (MnAs) on silicon and sitall substrates with Mn concentration of 5.8–16.4 at were obtained by vacuum-thermal evaporation. The structural properties of the films were investigated by X-ray phase analysis and scanning electron microscopy. Magneto-optical properties were studied using the transverse Kerr effect (TKE) method in the energy range of 0.5–4.0 eV in magnetic fields up to 3 kOe at temperatures of 20–300 K. In the geometry of the transverse Kerr effect, the spectral, field, and temperature dependences of TKE were obtained. Analysis of experimental data showed that at Mn contents more than 12.9 at the films contain the -phase of the topological Dirac semimetal Cd As in the form of large granules, as well as ferromagnetic MnAs granules. The Curie temperature of the films depends on their Mn content and is lower than that of bulk MnAs samples. At Mn contents in the film of 5.8 and 6.4 at , no magneto-optical response was detected, indicating the formation of a superparamagnetic state or a spin glass state at low Mn concentrations. At an Mn content in the film of 9.9 at , a significant change in magneto-optical spectra was observed, indicating the formation of MnAs nanoclusters and partial dissolution of Mn in the Cd As matrix. [ABSTRACT FROM AUTHOR]

A scaling behavior of the anomalous Hall effect resistivity ρAHE versus the longitudinal resistivity ρ in (CoFeB)x(LiNbO3)100 −x nanocomposites with a low content of dispersed Co and Fe atoms (Nd ~ 4 × 1020 cm−3) in an amorphous LiNbO3 matrix is studied in the range x ≈ 40–48 at % below the percolation threshold xp ≈ 49 at %. A logarithmic temperature dependence of the conductivity σ ~ lnT has been observed in the range x ≈ 44–48 at %, which is transformed in the range x ≈ 40–42 at % to a square root law lnσ ∝ ‒(T0/T)1/2, which is characteristic of cotunneling transport processes in nanocomposites. It has been found that the exponent n ≈ 0.24 in the scaling law ρAHE/x ∝ [ρ(x)]n coincides within an accuracy of 5% with the exponent n in a similar dependence for nanocomposites based on the (CoFeB)x(Al2O3)100 −x matrix with a high content Nd ~1021–1022 cm–3 and with the exponent n in a parametric dependence ρAHE ∝ [ρ(T)]n for the samples with the minimum content x ≈ 40 at %. The found features are attributed to the correlated change in the probability of cotunneling transitions in a set of more than three centers under the effect of spin–orbit coupling. The manifestation of the barrier tunneling anomalous Hall effect at granule interfaces is also p-ossible. [ABSTRACT FROM AUTHOR]

A strongly nonmonotonic temperature dependence of the magnetoresistance in (CoFeB)x(LiNbOy)100 –x film nanocomposites (x ≈ 40–48 at %) is observed in the temperature range of 3–250 K at the magnetic field up to 14 T near the percolation threshold on its insulating side. The magnetoresistance has a minimum at 40 K and increases steeply on cooling. Such behavior of the magnetoresistance is attributed to the coexistence of superferromagnetic regions with exchange-coupled granules separated by regions with superparamagnetic granules in the nanocomposite. In this case, an increase in the negative magnetoresistance at T > 40 K is due to the destruction of superferromagnetic ordering, whereas an increase in the magnetoresistance at T < 40 K is related to the processes involving simultaneous elastic tunneling via the chains of granules. At the saturation of the magnetization, an additional negative contribution arises, which is probably due to the quantum interference effects. At T < 4 K, a double-well shape of the field dependence of the magnetoresistance is observed, which could be attributed to the effect of a positive contribution that competes with the negative magnetoresistance. [ABSTRACT FROM AUTHOR]

We present results of magneto-optical investigations of (CoFeZr) x (Al2O 3 ) 1 0 0 − x film nanocomposites in transverse Kerr effect (TKE) geometry in the spectral range 0.5–4.0 eV and magnetic field up to 3.0 kOe. Nanocomposites were deposited onto a glass-ceramic substrate by ion-beam sputtering. The TKE response at room temperature strongly depends on the wavelength of light, applied magnetic field H and the volume metallic fraction. From the analysis of the field dependences of TKE at different wavelengths, it follows that in the as-deposited samples, the interaction between nanoparticles at x < 3 0 at.% is small and the nanocomposite is an ensemble of superparamagnetic particles; as x increases to 32 at.%, a superspinglass-type state arises, then, in the vicinity of 34 at.%, along with individual superparamagnetic particles, superferromagnetic regions appear. Long-range ferromagnetic order arises at concentrations x less than the percolation threshold for conductivity x per = 4 2. 6 at.%. In the presence of two different magnetic states in the samples, TKE is not proportional to the magnetization. Both the field dependences at near-infrared region and the spectral dependences of TKE change significantly after annealing of the samples, while the changes in the field dependences of the magnetization are almost imperceptibly. [ABSTRACT FROM AUTHOR]

Magnetostructural transition was observed in Ni-Mn-In-Cr Heusler alloy with help of Magnetic Force Microscopy (MFM). The crystal structure of a sample and characteristic temperatures of the phase transition were controlled by roentgenostructural phase analysis and magnetometry, respectively. It appeared prominently important to prepare the surface of the sample until the nanometer level of surface roughness. Magnetic study performed with scanning probe microscope revealed existence of magnetic domains, which were spread across the surface evenly. Further studies revealed that intensity of magnetic signal decreases as fading out of the contrast of the MFM images. It was found that location of domains shifted after the heating/cooling cycle above Curie temperature for the studied alloy. Location of new domain walls appeared correlating with surface scrapings and defects, whilst it became independent from those after heating until just 70°C. The mechanism behind the observed transition is proposed.

We present the results of the studies of magnetic and magnetocaloric (MCE) properties of quaternary Heusler alloys Ni48.5Mn35In15Co1.5 and Ni50Mn35In13.5Al1.5 in temperature range between 80 K and 400 K. While doping initial ternary Ni-Mn-In alloy with 1.5 at.% Al does not change TCA as well as MS, doping with 1.5 at.% Co significantly increases both TCA and MS. The direct magnetocaloric measurements around martensitic transition and austenite Curie temperature reveal the competition between the contributions of different signs. The latter is related to the vicinity of transition temperatures of austenite and martensite, resulting in mixed state, where both phases undergo magnetic order-disorder transformation in the same temperature region. Additionally temperature dependencies of adiabatic temperature change ΔTad and magnetic entropy ΔSM of the system exhibit additional peak feature which we attribute to intermartensitic transition occurring in these alloys.