Pressure Dependence Of Magnetic Properties Research Articles

Pressure dependence of magnetic properties in Fe–Mn–B amorphous alloys: evidence for inhomogeneous ferromagnetism

The pressure dependence of the saturation magnetization and Curie temperature was studied in melt-spun Fe60Mn20B20, Fe56Mn24B20 and Fe75B25 amorphous alloys up to 0.9 GPa, corresponding to volume changes up to 0.45%. In addition, in situ high-pressure (up to 40 GPa) x-ray diffraction was performed to determine the compressibility of the latter two alloys. Both the Curie temperature TC (at atmospheric pressure TC = 201 ± 3 and 159 ± 3 K) and the low-temperature saturation magnetization M5 K,5 T decrease remarkably with increasing pressure: dTC/dp =− 31 ± 0.5 and −32 ± 5 K GPa−1 and dlnM5 K,5 T/dp =− 0.15 ± 0.02 and −0.13 ± 0.03 GPa−1 for xMn = 20 and 24 at.%, respectively. Compared to dlnM5 K,5 T/dp =− 0.016 ± 0.003 GPa−1 measured for Fe75B25, the pressure dependence of M5 K,5 T is one order of magnitude larger in the ternary alloys. The bulk moduli for the Fe56Mn24B20 and Fe75B25 glasses were measured to be 152 GPa and 173 GPa, respectively. These data are also compared with the pressure dependence of the hyperfine field and theoretical calculations of the saturation moment for Fe–B alloys reported in the literature. The results were interpreted within an inhomogeneous itinerant-electron model of ferromagnetism.

Electronic structure and pressure dependence of magnetic properties of Fe/N/Fe multi-layers

The electronic structure and magnetic properties of the Fe/N/Fe multi-layers were obtained by means of self-consistent band structure calculations employing the Linear Muffin-Tin Orbital method (LMTO). Calculations were carried out for several lattice parameters in order to obtain ground-state properties such as equilibrium lattice parameters and the critical pressure of these multi-layers. The analysis of the density of states at equilibrium volume gives a good understanding of the electronic and magnetic properties of these multi-layers, showing remarkable differences from the bulk properties of iron-based nitrides. Ferromagnetic calculations show that the Fe/N/Fe multi-layers, at equilibrium volume, have a ferrimagnetic order of 1.45 μB and −0.22 μB as the magnetic moments at the two non-equivalent iron sites. At nitrogen sites a moment magnetic of −0.16 μB was found, which is opposite to the very small values found in bulk iron nitrides. The magnetic moment and hyperfine field (the Fermi Contact) show a strong dependence with the lattice spacing with a collapse of the magnetic moments at certain critical lattice spacing.

Pressure dependence of magnetic properties of CrO 2 from theory

From self-consistent electronic structure calculations bulkmodulus of CrO 2 (270 GPa) is within agreement of experimental value 280 ± 20 GPa. At different simulated isotropic compressions the system remains half metallic for 1 < P < 60 GPa then becomes metallic with lowered magnetization for 60 < P < 120 GPa. This is accompanied by decreasing energy difference between the ferromagnetic ground state and an antiferromagnetic configuration so that both are accessible at high pressures. Spin fluctuation theory analysis points to critical pressure for magnetic order disappearance P C = 150 GPa and d T C/d P = −0.027 K GPa −1. This positions CrO 2 between soft (Invar) and very hard (fcc–Ni) magnetic systems pointing to its magnetic hardness.

Pressure effect on some magnetic properties of the HfFe6Ge6-type ScMn6Sn5.45In0.55, YMn6Sn5.65In0.35 and LuMn6Sn5.1In0.9 compounds

Temperature and pressure dependence of magnetic properties of HfFe6Ge6-type ScMn6Sn5.45In0.55, YMn6Sn5.65In0.35 and LuMn6Sn5.1In0.9 compounds are reported. The three compounds are characterized by similar magnetic properties. At ambient pressure, they order ferromagnetically about the room temperature (293⩽Tc⩽356K) and undergo a ferro- to helimagnetic transition upon cooling (235⩽Tt⩽327K). The external pressure acts in the same way for all three compounds. The increase of pressure yields a linear increase of Tc and a decrease of Tt. The present results are discussed and compared with the corresponding properties of the isotypic compounds RMn6Ge6−xGax (R=Sc, Y, Lu).

Pressure and magnetic field effect on magnetic properties of RMn6Ge6–x Gax (R = Y, Sc, Lu) solid solutions

AbstractTemperature and pressure dependence of magnetic properties in YMn6Ge6–xGax for x = 0.56, ScMn6Ge6–xGax for x = 0.65 and x = 0.75 and LuMn6Ge6–xGax for x = 0.6 and x = 0.7 are reported. For the first three compounds the external pressure causes an increase in the Néel temperature while for Lu compounds dTN/dP = 0. Only for LuMn6Ge5.35Ga0.65 the external pressure changes the magnetic properties at low temperatures.

Pressure effect on magnetic properties of NdMn 2− xFe xGe 2 (0.1⩽ x⩽1.0) series of solid solutions

Temperature and pressure dependence of magnetic properties in the NdMn 2− x Fe x Ge 2 series of solid solutions (0.1⩽ x⩽1.0) are reported. The ( P, T) magnetic phase diagrams are determined on the basis of the AC magnetic susceptibility measured in a weak magnetic field. The measurements were carried out under hydrostatic pressure up to 1.5 GPa in the temperature range 80−430 K. The reported data show that in the studied series of solid solutions, a drastic change in magnetic properties takes place in a narrow dilution parameter range (0.4⩽ x⩽0.5). While taking into account the magnetic properties, the studied range of Fe content could be divided into four regions. Only in the case of x=0.3 and 0.4, the external pressure significantly influences the magnetic properties of the samples.

Pressure dependence of magnetic properties of Fe 4N and Mn 4N

The value of the magnetization of ferromagnetic Fe 4N is found to decrease under pressure while that of ferrimagnetic Mn 4N increases. The magnitude of the effective field at the 55Mn nucleus of the Mn(I) site of Mn 4N also increases under pressure. It is deduced that the magnitude of the moment at the Mn(II) site decreases under pressure, while that of the Mn(I) site is independent of pressure, in agreement with the model of covalent magnetism for Mn 4N.

Pressure dependence of magnetic properties of Nb 1− yFe 2+ y

The pressure dependence of magnetic properties was investigated in antiferromagnetic (stoichiometric) and ferromagnetic (off-stoichiometric) NbFe 2 with the C14 Laves phase structure.

Magnetic properties of NdSb, GdSb, TbSb, DySb, HbSb and ErSb under hydrostatic pressure

The hydrostatic pressure dependence of magnetic properties are reported for antiferromagnetic RSb where R = Nd, Gd, Tb, Dy, Ho or Er. Measurements were made for pressures 0 ≤ p ≤ 10 kbar, magnetic fields 0 ≤ H 0 ≤ 60 kG, and temperatures 1.4 K ≤ T ≤ 35 K. dT N/dP shows no systematic trend and ranges from -0.038 K/kbar for DySb to + 0.21 K/kbar for NdSb. The magnetic properties of DySb are strongly P-dependent, whereas those of HoSb are P-independent, but sample-dependent.