Mixed Magnetic Phase Research Articles

Magnetic properties of singlet ground states in RM2X2 compounds

A simple survey of the magnetic properties of new tetragonal RM2X2 compounds is given. Particular attention is paid to the interaction of Crystal Field in the case of nonmagnetic singlet ground states. A number of physical effects which result from this situation are discussed. In particular, the nature of this type of ground state is proved to be indispensable for the existence of amplitude magnetic structures at 0 K and for the most amazing of mixed magnetic phases, in which Rare Earth ions with two magnetic states are involved. Evidence of this behaviour through several examples in such compounds as PrNi2Si2, TbNi2Si2, TbRu2Si2 and TbRu2Ge2 from the joint analysis of different magnetic properties will be presented.

Mixed magnetic phases in tetragonal

A careful analysis of neutron diffraction experiments under magnetic field performed on a single crystal of tetragonal is presented. It shows that the zero-field-low-temperature magnetic phase is not the natural compensated antiphase structure proposed so far for the Q = (3/13, 0, 0) propagation vector, but a mixed phase where the moment of two of the 26 Tb sites of the unit cell vanishes. The magnetic structures of the first three field induced phases of the multistep metamagnetic process agree with previous analysis whereas the fourth field induced phase is not the non-mixed proposed one but a mixed one with two zero moments as in zero field. Contrary to previous interpretations, the transition at 4.7 K observed by specific heat and susceptibility corresponds to the change of the magnetic structure from the mixed low-temperature one to a slightly modulated non-mixed one. Numerical simulation allowed us to account for the main properties observed and emphasizes the crucial role of the crystal field.

Evidence of mixed magnetic phases inTbRu2Ge2

In compounds with normal rare earths at the same crystallographic site, mixed magnetic phases with two distinct rare-earth magnetic states, namely, a zero moment one and another with a high moment, can be stabilized at low temperature not only in zero applied field but also in different field-induced magnetic phases of a metamagnetic process. These characteristics are observed in tetragonal ${\mathrm{TbRu}}_{2}{\mathrm{Ge}}_{2}$ from neutron diffraction and magnetization measurements on a single crystal. It is shown that such magnetic structures may originate from a moment instability due to the crystal field in the presence of frustrated exchange interactions. Numerical simulations using the periodic-field model allowed us to satisfactorily account for the observed properties and emphasize the crucial role played by the crystal field.

A Mössbauer spectral study of Nd6Fe13X, where X is Cu, Ag, and Au and of the spin reorientation in Nd6Fe13Si

The Mössbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 80 and 500 K. A model corresponding to a basal alignment of the magnetic moments leads to excellent, internally consistent, fits for the Cu, Ag, and Au compounds. The resulting temperature dependences of the spectral hyperfine parameters are uniform and reveal for each Fe site the expected correlations between the isomer shift and the Wigner–Seitz cell volume and the hyperfine field and the number of Fe near neighbors. For Nd6Fe13Si, a different model must be used because of the presence of a spin reorientation below 155 K. Above 155 K, because of the axial alignment of the moments, and in agreement with the 295 K powder neutron diffraction results, the spectra can be analyzed with four sextets. Below 155 K, five additional sextets are required to fit the spectra because of a progressive transition towards a basal alignment of the Fe moments. At 80 K the mixed magnetic phase is 75% basal and 25% axial, whereas at 110 K the mixture is 50:50. The hyperfine parameters of the basal and axial sextets found for Nd6Fe13Si are consistent with those found for the basal Cu, Ag, and Au compounds and those observed for basal Nd6Fe13Sn. The lattice properties of the compounds, obtained from the temperature dependences of the isomer shift and the spectral absorption area, are consistent with the Wigner-Seitz cell volumes and the bonding of each crystallographically distinct Fe site. The magnetic anisotropy of a variety of Nd6Fe13X compounds is controlled by the s-p hybridization of the Nd–X bonds, a hybridization which is very sensitive to the electronic configuration of X.

Magnetic properties and magnetic phase diagram of the frustrated Co1-xFexPt3 compounds.

The investigation of the magnetic properties of the pseudobinary ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Pt}}_{3}$ L${1}_{2}$ ordered compounds resulting from alloying the ferromagnet ${\mathrm{CoPt}}_{3}$ and the frustrated antiferromagnet ${\mathrm{FePt}}_{3}$ is reported. dc susceptibilities and zero field cooled and field cooled magnetizations as a function of temperature and field (0--35 T) have been investigated. On the Co-rich side (x0.6), the compounds display a long-range ferromagnetic order characterized by the occurrence of two reentrant spin-glass phases (or mixed magnetic phases) at low temperature and magnetic field starting at very low iron concentration. This ferromagnetic region is closed by a multicritical point located around x=0.55 and T=120 K. On the iron-rich side, an antiferromagnetic region with two antiferromagnetic [1/21/20] and [1/200] structures is observed for 1\ensuremath{\ge}x\ensuremath{\gtrsim}0.8. Beyond 0.8 the basic antiferromagnetic order [1/21/20] changes progressively into a spin-glass ordering and the less stable one [1/200] persists at low temperature up to Fe concentrations as high as 0.6. Although the complex behavior of the iron-rich side in the intermediate region is not totally elucidated, a tentative phase diagram is proposed and discussed comparatively with the previously determined (Fe-Mn)${\mathrm{Pt}}_{3}$ and (Co-Mn)${\mathrm{Pt}}_{3}$ phase diagrams. The occurrence of a spin-glass phase that separates the long-range ferromagnetic region from the antiferromagnetic one is specific to the (Co-Fe)${\mathrm{Pt}}_{3}$ system in agreement with theoretical models. The (Co-Fe)${\mathrm{Pt}}_{3}$ appears as the most frustrated among the three systems considered. \textcopyright{} 1996 The American Physical Society.

Mixed magnetic phase in Co-rich metallic glasses

ac susceptibility (χ) and magnetoresistance (MR) have been measured in Co-rich amorphous ferromagnets [Fe5Co50Ni17−xCrx(BSi)28 (x=0,5,10,15), Fe5Co50Mn17(BSi)28, and Fe7.8Co31.2Ni24Mn15(BSi)22] to understand the changes in magnetic phase brought by the addition of Cr/Mn. The Tc decreases monotonically with Cr/Mn addition. Samples with x=0–15 remain ferromagnetic down to 16 K. But for the Mn substituted samples below 80 K, χ decreases drastically and at 16 K it is only 5% of its value at 80 K indicating spin freezing. dc magnetization data show a peak around 30 K as well as a time dependence in the Mn17 sample. Presence of significant ferromagnetic anisotropy of resistance (FAR) even at the lowest temperature for both Mn-containing samples indicates that ferromagnetism persists even when transverse spin freezing is present. With lowering of temperature FAR increases, and below 30 K it should have decreased considerably if the lowest temperature phase was purely spin-glass-like but here it remains almost constant. The high-field slopes for T < Tc in both orientations are negative. In particular, for Mn15 sample the slope has a broad maximum decreasing on both sides as T → Tc and T<80 K. This behavior is interpreted in terms of a transverse spin freezing. We conclude that the lowest temperature (<30 K) phase in samples containing Mn is a mixture of spin-glass and long-range ferromagnetism. Samples containing Cr show a large positive slope for T < Tc and a very low FAR. The ratio Δρ∥/Δρ⊥ (≂0) indicates that the domain magnetization lies in the ribbon plane and is parallel to the ribbon axis.

Magnetic history of hexanediammonium tetrachloroferrate(II)

The magnetic susceptibility of the two-dimensional antiferromagnet (CH 2) 6(NH 3) 2 FeCl 4 is reported. The compound has unusual dependence on its magnetic history below its Neel temperature T N. Though the magnetic ordering is associated with a structural distortion, this distortion does not seem to explain the magnetic behaviour of the compound. The results have been interpreted in terms of mixed magnetic phases which are likely to exist when the sample is cooled in a magnetic field.

Mixed magnetic phases and the equilibrium B (T) phase diagram of concentrated PtMn spin glasses

The field cooled magnetization, the TRM and the IRM of PtMn spin glasses (10, 15 at% Mn) are measured in fields B = 0.3 mT-3 T between 1.5 and 300 K. From the data a magnetic phase diagram in the B(T) plane is deduced containing two phase transition lines Tf(B) and Bc(T).

Magnetic phase diagram of GdAg1− xZnx

The magnetic phase diagram of GdAg 1− x Zn x , an intermetallic solid solution of an antiferromagnet ( GdAg: T N = 136 K) and a ferromagnet ( GdZn: T C = 269 K), has been elaborated from magnetization measurements. The antiferromagnetic phase boundary T N( x) first passes a broad maximum meeting the ferromagnetic phase boundary T C( x) at x 1 = 0.575 and T 1 = 72 K, where four phases coexist. On approaching ( x 1, T 1) along T N( x) the magnetization phenomena vanish. At x 1 the phase transition still has ferromagnetic appearance but proceeds into a state without spontaneous magnetic moment. Two different ferromagnetic phases (F 1, F 2) and one ferrimagnetic phase (F 3) occur in the composition intervals 0.69 < x 1 <1, and 0.61 < x 2 < 0.69 and 0.51 < x 3 < 0.61. All phase transitions seem to be of second order except th e F 1− F 2 one at x = 0.69 which is of first order. This phase line meets the paramagnetic to ferromagnetic phase boundary T C( x) in a multicritical point with the coordinates x m = 0.69, T m = 123 K. Six further mixed magnetic phases, M 1, 2, ..., 6, are observed between x = 0.33 and 0.6 below the antiferromagnetic branch and exhibit irreversible thermodynamic properties, such as hysteresis, below about 40 K. Assuming local magnetic interactions only between nearest and next-nearest Gd neighbours, the T N( x) and T C( x) phase boundaries can be described fairly well by a simple model calculation using different exchange parameters for a few relevant distributions of Ag and Zn atoms.

Abstract: Evidence for a mixed magnetic phase in the system Ce1−xPrxAl2

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