Relaxation Of Remanent Magnetization Research Articles

Features of Relaxation of the Remanent Magnetization of Antiferromagnetic Nanoparticles by the Example of Ferrihydrite

The relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles at the exchange bias effect implemented in these systems has been investigated. The magnetization relaxation depends logarithmically on time, which is typical of the thermally activated hoppings of particle magnetic moments through the potential barriers caused by the magnetic anisotropy. The barrier energy obtained by processing of the remanent magnetization relaxation data under the field cooling conditions significantly exceeds the barrier energy under standard (zero field cooling) conditions. The observed difference points out the possibility of using the remanent magnetization relaxation to analyze the mechanisms responsible for the exchange bias effect in antiferromagnetic nanoparticles and measure the parameters of the exchange coupling of magnetic subsystems in such objects.

Influence of Tempering Temperatures on Magnetoelastic Relaxation Behavior of 30KH13 Steel

Magnetoelastic tests of 30KH13 (30X13) steel were carried out under cyclic loadings. The article focuses on the property of magnetoelastic power relaxation of remanent magnetization. With the load amplitude increasing, complexes of power approximation coefficients reflect typical mechanical loads at various tempering temperatures.

Magnetic reversal dynamics of NiFe-based artificial spin ice: Effect of Nb layer in normal and superconducting state

Square arrays of artificial spin ice (ASI) constituting weakly interacting NiFe nano-islands, with length ∼312 nm, width ∼125 nm, thickness ∼20 nm, and lattice constant ∼570 nm, were fabricated on Nb thin film and on thermally grown 300 nm SiO2 on silicon. Detailed investigations of magnetic force microscopy (MFM) at room temperature, and magnetization M(H) loops and relaxation of remanent magnetization (Mr) at various temperatures were carried out in two in-plane field geometries, namely, parallel (“P”-parallel to the square lattice) and diagonal (“D”- 45° to the square lattice). The magnetic response of the ASI samples shows striking difference for insulating (SiO2), metallic (Nb, T > 6.6 K) and superconducting (Nb, T < 6.6 K) bases, and the field geometry. For instance, with the Nb base in the normal metallic state (T > 6.6 K), (1) in “P” geometry the M(H) loops are found to be more “S” shaped in comparison with that for SiO2 base; (2) the ratio of magnetic vertex population of Type II to Type III vertices extracted from MFM studies in “P”(“D”) geometry is ∼1:1.1(1.2:1) that changed for the SiO2 base to ∼2.1:1 (4: 1). However, the NiFe-ASI on both metallic Nb and SiO2 bases exhibit a highly athermal decay of magnetization, and the % change in Mr in about two hours at T = 10 K (300 K) lies in a range of ∼1.07–1.80 (0.25–0.62). With Nb base in superconducting state (T < 6.6 K), the M(H) loops not only look radically different from those with SiO2 and metallic Nb as bases but also show significant difference in “P” and “D” geometries. These results are discussed in terms of inter-island magnetostatic energy as influenced by field geometry, presence of metallic Nb base and competing vortex pinning energy of superconducting Nb base.

Anisotropy of amorphous nanogranular composites CoNbTa-SiO n and CoFeB-SiO n

A comparative investigation of the magnetic properties of amorphous nanogranular composites (Co41Fe39B20)x(SiOn)100 − x and (Co86Nb12Ta2)x(SiOn)100 − x has been performed in the subpercolation region at temperatures in the range 4.2–300 K. The thermomagnetic dependences in the range 4.2–300 K and the processes of magnetization reversal and remanent magnetization relaxation at liquid-helium temperatures have been studied. It has been established that the average anisotropy constants of amorphous nanograins are equal to 3.6–7.0 kJ/m3 for the (Co41Fe39B20)x(SiOn)100 − x composites and 5–8 kJ/m3 for the (Co86Nb12Ta2)x(SiOn)100 − x composites. The fundamental differences in the concentration dependences of the anisotropy constant Keff and the coercive force HC have been revealed for the two systems under investigation. It has been demonstrated that, as the concentration of the metal phase increases, the quantities Keff and HC increase for the (Co86Nb12Ta2)x(SiOn)100 − x composites and decrease for the (Co41Fe39B20)x(SiOn)100 − x composites.

Vortex dynamics in heavy fermion CeCoIn5

Local magnetic measurements utilizing a micro-Hall probe were performed on a superconducting heavy fermion CeCoIn5 single crystal. We show that the critical current follows a power law as predicted by Ginzburg–Landau theory. This behavior is found to be universal in different heavy fermion and high-Tc superconducting materials. Furthermore, we report on remanent magnetization relaxation showing a high relaxation rate with approximately linear temperature dependence. Although qualitatively similar to another undoped heavy fermion, UBe13, this relaxation rate is significantly higher, providing evidence that CeCoIn5 can be grown in the clean limit.

Magnetism of Ti4+ diluted manganites La1−xPbxMn1−yTiyO3 (y⩽x)

The effect of nonmagnetic Ti4+ substitution for Mn4+ on magnetic ordering of La1−xPbxMn1−yTiyO3 (x=0.15,0.26, and 0.4; 0⩽y⩽x ) has been studied. The ferromagnetic transition temperature and the magnetization decrease with increasing amount of titanium. Complete substitution of Mn4+ by Ti4+, for x=y, excludes the Mn3+–O–Mn4+ double exchange. However, these compounds still show ferromagnetism if the dilution of the Mn sublattice by Ti is small enough (y⩽0.2). This ferromagnetism probably originates from a ferromagnetic Mn3+–O–Mn3+ superexchange. A thorough study of magnetic properties including AC magnetic susceptibility, magnetization, temperature dependence of coercivity and relaxation of remanent magnetization has been carried out and gives evidence of cluster spin glass behaviour for La0.6Pb0.4Mn0.6Ti0.4O3.

Spin-glass behavior in LiMn2O4 spinel

LiMn 2 O 4 spinel exhibits spin-glass behavior below 25 K. A cusp in the ac susceptibility appears at 25 K, below which the susceptibility increases with decreasing frequency. The dc magnetization shows irreversibility, and relaxation of remanent magnetization is seen on the macroscopic time scale. The randomness and frustration necessary for spin-glass behavior are explained in a manner compatible with the cation and charge ordering present in this material.

Single vortex creep in Tl2Ba2CaCu2O8 epitaxial thin films.

By measuring the magnetization hysteresis loops and the remanent magnetization relaxation for an epitaxial ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ thin film, we determined the temperature dependence of the experimental critical current density j(T) and the normalized relaxation rate S(T) at ${\mathit{B}}_{\mathit{e}}$=0.4 T. It is shown that the data j(T) and S(T) can be well fitted to the single vortex creep model with only one fitting parameter in each fitting process. The data j(T) and S(T) were then used as the input for the generalized inversion scheme (GIS); the output of the GIS, i.e., the temperature dependence of the true (unrelaxed) critical current density ${\mathit{j}}_{\mathit{c}}$(T) and the pinning potential ${\mathit{U}}_{\mathit{c}}$(T), follows the theoretical expressions predicted by the single-vortex collective pinning model. Finally, the magnetization (and thus the current) dependence of the activation energy U(${\mathit{M}}_{\mathit{T}=0}$, T=0) was determined by using the magnetization relaxation data. Again, the single vortex creep model explains the resulting U(${\mathit{M}}_{\mathit{T}=0}$, T=0 K) relation very well. \textcopyright{} 1996 The American Physical Society.

Fishtail effect and small size normal core pinning in melt-textured-growth YBa2Cu3O7−δ bulks

By measuring the magnetization hysteresis loops and the remanent magnetization relaxation for a melt-textured-growth YBa2Cu3O7−δ bulk with two different oxygen concentrations, we found that the extra oxygen deficiencies enhance the flux pinning and the fishtail effect in low and intermediate temperature region. This strongly suggests that the fishtail effect is related to the elementary pinning centers. A model concerning the nonuniform distribution of upper critical field among the pinning sites is proposed to explain the fishtail effect. Finally, we present some evidence to support this model.

Low-temperature magnetic relaxation of organic coated NiFe2O4 particles

We report measurements of relaxation rate of the remanent magnetization versus temperature for NiFe2O4 particles coated with the surfactant oleic acid. It has been reported that the organic coating induces a strong surface anisotropy resulting in surface spin canting and anomalous hysteresis properties at low temperature as compared to the bulk material. We have measured, at temperatures down to 400 mK, relaxation of remanent magnetization which extrapolates to a nonzero value at zero temperature. Macroscopic quantum tunneling at these temperatures has been predicted and observed only for materials with high magnetocrystalline anisotropy, so it is particularly interesting to observe it in NiFe2O4, which has a relatively low bulk anisotropy. It is suggested that the strong surface anisotropy induced by the organic coating may be responsible for tunneling in these particles.

The relaxation of the monodomain TmBa 2Cu 3O x single crystal magnetization in the superconducting state

Measurements of the remanent magnetization relaxation RM( t) in the monodomain TmBa 2Cu 3O x single crystal are reported. The relaxation rate r( T) = d RM( T, t)/d(ln t) has a sharp maximum at temperature T = T max. The T max value is about 15 K for H = 2.8 kOe and it strongly depends on the magnitude of the applied magnetic field being shifted to higher temperatures as H is decreased. The normalized rate r( T)/ RM 0 in contrast to the r( T) behavior, is almost isotropic irrespective of the H direction. The r( T) maximum is qualitatively reproduced by the calculation taking into account the thermal activated flux creep and Abrikosov vortices distribution according to the Bean model.

Time relaxation of the untwinned TmBa2Cu3O7−δ single crystal remanent magnetization

Measurements of the remanent magnetization relaxation M(t) in the TmBa2Cu3O7−δ single crystals with the small twins density are reported. The relaxation rate r(T)=dM(T.t)/d(lnt) has a sharp maximum at temperature T=Tmax. The Tmax value shifts to lower temperatures as H is increased. The r(T) maximum is reproduced by the calculation taking into account the thermal activated flux creep and the Abrikosov vortices distribution according to the Bean's model.