Spontaneous magnetization of Fe - Mn - B Amorphous alloys under high pressures

Abstract

We have investigated the influence of high pressure (up to 2 GPa) on the spontaneous magnetization of six Fe_80-x Mn_x B₂₀ alloys (x = 6, 10, 15, and three alloys with x close to 20). In all cases a decrease of spontaneous magnetization with pressure was noticed, in some considerable.     

The influence of pressure on spontaneous magnetization of Fe60Mn20B20 amorphous alloy at temperature range 77.4–300 K

Abstract

Amorphous, ferromagnetic, invar like, Fe₆₀ Mn₂₀ B₂₀ alloy has been investigated. Two kinds of experiments were carried out for this alloy. The first, using high pressure technique, revealed the influence of pressure on B(H) dependencies within the wide range of temperature under pressure of 0.5 GPa. From the magnetization curves obtained during these experiments the decrease of spontaneous magnetization caused by applied pressure 0.5 GPa at temperature -180°C has been calculated at the rate about 7 10^?11T/Pa.

In the second kind of experiments the measurements of volume magnetostriction up to 720 kA/m magnetic field intensity have been done. Volume magnetostriction coefficient at temperature 77.4 K has been determined to be about 2 10^?11 [A/m]^?1.     

Pressure dependence of the magnetization of NiFe3N

Abstract

The experimental result of the decrease of the magnetization with pressure within the ordered nitride NiFe₃N is addressed using the A.S.W. (augmented spherical wave) method. Among the two magnetic sublattices i.e. Ni and Fe in the structure only the latter is found responsible of the pressure dependence of the magnetization.     

Study of matter at high pressure using small angle scattering and depolarization of neutrons

Abstract

The method of studying matter under high pressure using the measurement of the transmitted neutron beam is proposed. Method is based on the very small angle scattering and depolarization of neutrons combined with the anvil pressure technique. Test experiments have been carried out demonstrating feasibility of the method for studying phase transitions accompanied with the change of density or magnetization and equations of state. The obtainable pressure range of the method is discussed.     

Magnetization of Gd cluster: Anomalous thermal behavior

Theoretical studies of the temperature (T) dependence of magnetization of Gd₁₃ clusters have been carried out within a classical Heisenberg model using Monte-Carlo simulations. It is shown that for a broad range of values of , defined as the ratio between competing ferro and anti-ferro magnetic couplings, the cluster magnetization increases with T in the low T region, as seen in experiment. The clusters are also shown to exhibit a wide distribution of moments at a given T, which broadens significantly with increasing T. It is suggested that this may affect the observed magnetic behavior of magnetic clusters in Stern-Gerlach experiments. Received 29 May 1999 and Received in final form 5 September 1999     

Transport and magnetic properties of a Zn<Subscript>0.1</Subscript>Cd<Subscript>0.9</Subscript>GeAs<Subscript>2</Subscript> + 10 wt % MnAs composite with magnetic clusters at high pressure

The temperature (T = 77–420 K) dependences of the electrical resistivity and the magnetization, the magnetic-field (H ≤ 5 kOe) and pressure (P ≤ 7 GPa) dependences of the resistivity, the Hall coefficient, and the magnetization have been measured in the Zn_0.1Cd_0.9GeAs₂ + 10 wt % MnAs composite with the Curie temperature T _C = 310 K. The magnetoresistive effect has been observed at high hydrostatic pressure to 7 GPa. At nearly room temperature, the pressure dependence of the magnetization demonstrated a transition from the ferromagnetic to paramagnetic state at P ~ 3.2 GPa that was accompanied by the semiconductor–metal phase transition.     

An influence of pressure on the ferromagnetic hall effect of some amorphous alloys

Abstract

The Hall resistivity curves Q₁₁(B) of Fe_80-x Mn_x B₂₀ (x=6, 10, 20) amorphous alloys have been investigated within the pressure up to 2 GPa showing considerable changes. The spontaneous magnetization changes have been calculated on this basis and compared with those obtained from classic method.     

Magnetostructural transition in NdCu2

The magnetic (H , T)-phase diagram of the orthorhombic compound NdCu₂ was investigated for external magnetic fields up to 15 T parallel to the crystallographic c-direction. Magnetization and magnetostriction measurements reveal an anomalous change of the magnetic properties as well as giant magnetostriction (GMS) and large hysteretic effects. This behaviour is similar to that observed in some other RCu₂ compounds where it has been interpreted as a conversion of the magnetic Ising axis. In contrast to these other RCu₂ compounds, however, the easy axis of magnetization in NdCu₂ is the b-axis. The macroscopic measurements are compared with neutron diffraction experiments which reveal GMS along the b-axis and a new magnetic phase with propagation vector in the converted crystal. Received 27 March 2000 and Received in final form 11 September 2000     

Magnetic anisotropy of a system of nanocrystalline BaO·6Fe2O3 particles

The anisotropy of a system of barium ferrite particles with an average diameter of 60 nm has been studied. The effective anisotropy constant has been determined in the temperature range from 4.2 K to T _c by the law governing approach to saturation magnetization. The observed deviation from the magnetocrystalline anisotropy constant is explained as due to a negative contribution of the “surface” anisotropy constant. An estimate is made of this contribution as a function of particle size. Fiz. Tverd. Tela (St. Petersburg) 40, 1894–1897 (October 1998)     

Dynamic magnetization of <Emphasis Type="Bold">γ</Emphasis>- nanoparticles isolated in an amorphous matrix

We have studied the magnetization of a system of γ-Fe₂O₃ (0.68 vol.%) nanoparticles isolated in an SiO₂ amorphous matrix placed in an alternating magnetic field with a frequency of 640 Hz and in the temperature range of (77-300) K. Compared to temperatures closer to 300 K (where the system has a superparamagnetic behaviour), at lower temperatures, the magnetization has a dynamic hysteresis loop due to the magnetization's phase shift between the field and the magnetization. The delay of the magnetization (attributed to the Néel relaxation processes) increases with the decrease of temperature. It has been shown that the relaxation time resulting from the Néel theory is determined by an effective anisotropy constant ( K ) that takes into account the magnetocrystalline anisotropy, as well as the shape, surface and strain anisotropies. In the following we will show that the surface and strain anisotropy components have the most significant influence. When the temperature decreases from 300 to 77 K, the relative increase of the saturation magnetization of the nanoparticles is much higher than that of the (spontaneous) saturation magnetization of bulk γ-Fe₂O₃. This increase is due to the increase of the mean magnetic diameter of the particles attached to the core of aligned spins, from 10.16 nm to 11.70 nm, as a result of the modification of the superexchange interaction in the surface layer. Received 25 April 2002 / Received in final form 11 August 2002 Published online 14 February 2003 RID="a" ID="a"e-mail: ccaizer@physics.uvt.ro     

Sm2(TM)17合金的磁性(自旋再取向相变)研究

本文研究了Sm₂(FeNiCoM)₁₇合金(M为非磁性组元)的磁性。样品由六角结构无序型的2∶17主相及少量FeNi合金杂相组成。在六角结构的e轴方向(易磁化方向)观察到下述异常现象:低温(273K以下)时的磁化及反磁化曲线发生明显的跃变,跃变时相应的磁场H_r随温度下降而增大;磁滞迴线是蜂腰型的,温度愈低蜂腰愈明显;升温时磁化强度随温度变化(1.5K至居里点T_C)的曲线上出现极大值,其相应的温度T_t随磁场增大而降低;降温时观察到了热磁滞后现象。但在基面(难磁化方向)上及Co含量增多(>18at％)时,样品却表现了正常的铁磁行为。本文提出用磁矩非共线结构排列的自旋再取向相变来解释上述异常现象,并给出自旋倒向所需越过的能垒高度U=9.2×10^-15erg,用设想磁结构的模型得到的磁化强度的计算值与实验值也符合得较好。 关键词：     

Magnetic Moment of Fe and Magnetocrystalline Anisotropy of Fe-rich Intermetallic Compounds Under Pressure

Magnetization and magnetocrystalline anisotropy of Fe-rich R -Fe intermetallics ( R =Y and rare earths) have been studied under pressure up to 1 GPa in temperatures from 5 K to 350 K using a miniature CuBe pressure cell and a SQUID magnetometer. A decrease of Fe-moment under pressure depends strongly on local environment parameters such as a local atomic volume, local coordination of Fe-atoms and hybridization. The pressure-induced changes of magnetocrystalline anisotropy energy are caused by both, the pressure decrease of magnetization M S and the pressure effect on the crystal electric field interactions. The pressure experiments allow to distinguish both the effects.     

Light scattering studies of oleic acid under high pressure

Abstract

Elastic light scattering of oleic acid has been studied at room temperature and at pressures up to 0.5 GPa, where the strong scattering of radiation in the visible region occurs. For the application of pressure above 0.21 GPa the strong increase of the scattered light intensity has been observed some seconds after an application of pressure. More detailed analysis shows that Me theory is not sufficient to explain experimental results for size of Scattering particle greater than 18 μm.     

Magnetization of an electron plasma by microwave pulses: Faraday induction

It has been argued theoretically that the recently proposed vacuum fieldB ⁽³⁾ is not accompanied by a real electric fieldE ⁽³⁾ . Experimental evidence for this interence is available in the data reported by Deschampset al. [10], using microwave magnetization of an electron plasma set up in helium gas. Faraday induction due toB ⁽³⁾ does not occur in the inert gas and is not observed experimentally in the absence of free electrons. WheneverB ⁽³⁾ interacts with free electrons, however, Faraday induction occurs through a pulse of induced magnetization (i.e., induced orbital electronic angular momentum).     

Effect of noncrystallographic magnetic anisotropy on magnetization reversal in multilayer magnetic films

A study has been carried out of the magnetization of a layered system consisting of two exchange-coupled easy-axis ferromagnetic layers separated by a nonmagnetic spacer and having mutually perpendicular anisotropy axes. It is shown that the magnetization of such a system can undergo stepwise decrease with increasing magnetic field. The field dependence of the magnetization has a bifurcation point. The magnetization orientation can exhibit jumps in excess of 90° depending on the angle of magnetic-field orientation. Fiz. Tverd. Tela (St. Petersburg) 41, 660–664 (April 1999)     

Photoinduced changes in the space-modulated magnetic order of a FeBO<Subscript>3</Subscript>:Mg single crystal

An effect of nonpolarized white light on the modulated magnetic structure of a FeBO₃:Mg single crystal, which arises in this light-plane weak ferromagnet in the low temperature range during technical magnetization, has been revealed. It has been found that the degree of the light action on the magnetic state of FeBO₃:Mg depends both on its duration and on the orientation of the spontaneous magnetization vector M of the crystal during illumination. Interpretation of the results obtained has been performed in the context of the “magnetic ripple” theory on the assumption that the absorbed light induces additional uniaxial magnetic anisotropy in the easy plane of the crystal and that the anisotropy axis is collinear to the vector M during illumination.     

Investigation of Nd2CuO4 crystal structure at high pressure by neutron diffraction

Abstract

The crystal structure of Nd₂CuO₄ has been studied by neutron diffraction at pressure up to 5 Gpa. The volume compressibility value was determined as 5·6·10^?3/Gpa. The decrease of positional parameter of neodymium at high pressure has been observed. This structural change is explained by pressure induced neodymium ions charge increase.     

Direct measurement of magnetization isotherms of Fe64Ni36 Invar alloy in a diamond anvil cell

Magnetization isotherms of the Fe₆₄Ni₃₆ Invar alloy have been measured under pressure up to 5.3?GPa in magnetic field up to 5?T using a diamond anvil cell and SQUID magnetometer. The unambiguous change of the pressure parameter dlnM_S/dP (from ?9 to ?13×10^?2?GPa^?1) has been observed in a narrow pressure interval from 2.5 to 3.5?GPa at all temperatures in the range from 5 to 300?K. The pressure interval, where the sharp decrease in magnetization was observed, coincides with the critical pressures of the pressure-induced decrease in Fe-moment that were determined by the X-ray Magnetic Circular Dichroism and the X-ray Emission Spectra studies, recently. The pronounced decrease in the Curie temperature of the Fe₆₄Ni₃₆ alloy under pressure, dT_C/dP = ?44 ±2?K/GPa, has been confirmed.     

Mesoscopic oscillations of the magnetization near Ising impurity centers in strong magnetic fields

The frequency of orientational quantum oscillations of the magnetization near impurity-ion clusters with Ising properties in a saturated magnetic crystal is calculated. It is noted that in compounds of the type Ho_xY_3−x Fe₅O₁₂, where magnetic phase transitions are observed, additional magnetization reversal and magnetic resonance features due to mesoscopic oscillations of the magnetization can be observed at low concentrations x<0.001 and cryogenic temperatures in fields comparable to the intersublattice exchange interaction field. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 6, 445–448 (25 March 1997)     

Long time relaxation effect of liquid castor oil under high pressure conditions

Abstract

The relaxation times of Liquid castor oil have been investigated by observing the scattered light of a He-Ne gas laser during the slow or rapid application of pressure up to 0.7 GPa at 293 K. For the application of pressure above 0.36 GPa the strong increase of the scattered light intensity approximately by a factor of 10² has been observed 12 hours after an application of pressure. This pressure effect is also observed for subsequent pressure cycles, i.e., the pressure effect is reversible. Experimental results are interpreted according to a model of a liquid of long rod molecules.