I.Yu. Gaidukova

Magnetic instability of the Co sublattice in the Ho1−xYxCo3 system

Abstract X-ray thermal expansion, magnetic and electrical resistivity measurements of the pseudo-binary Ho 1− x Y x Co 3 system with PuNi 3 -type structure have been performed in a wide temperature range. Temperature-induced itinerant-electron metamagnetism has been observed in the concentration range 0.0⩽ x ⩽0.4 where the Co sublattice is in the strong ferromagnetic state at low temperatures. The transition was found to be sharper in the diluted compounds with a lower value of the transition temperature, which is in accordance with the nature of the observed effect. The temperatures of the spin-reorientation transition have been determined from low-field magnetisation measurements and the magnetic phase diagram of this system has been constructed.

Magnetic phase transitions in (Tb,Y)Mn2M2 (M=Ge and Si) systems

The temperature- and field-induced magnetic phase transitions in pseudoternary systems Tb1−xYxMn2Ge2 and Tb1−xYxMn2Si2, which are characterized by a separate magnetic ordering of the Mn and Tb subsystems, have been studied on strongly textured samples by magnetization and thermal expansion measurements. In the concentration region 0.4⩽x⩽1.0, where the Mn moments are ordered only, the magnetic structure is antiferromagnetic. The magnetic ordering in the Tb subsystem is accompanied by a transformation of the Mn magnetic structure. As a result, the compounds show a spontaneous magnetization. This transition is of a first-order type. In both systems the transition temperature for the Tb subsystem TC(Tb) decreases linearly with increasing Y concentration and goes to zero at about x=0.40. Canted phases and field-induced first-order transitions into the collinear phase have been observed in both systems below this temperature. It is concluded that the f–d exchange interaction is the primary factor governing the ...

Strongly enhanced thermal expansion in binary Y-Mn intermetallic compounds YMn2, Y6Mn23 and YMn12

Abstract For the three binary compounds YMn 2 , Y 6 Mn 23 and YMn 12 a strong temperature variation of the thermal expansion has been found with values of the coefficient α up to 55 × 10 −6 K −1 . This unusual behaviour of α ( T ) is referred to the existence of two sorts of Mn ionic states whose concentration changes with temperature.

Evolution of the magnetic behavior of the Co subsystem in YCo3 caused by small variations in stoichiometry and Al substitution

Abstract The phase composition at room temperature and the magnetization up to 55 kOe over the temperature interval 5–400 K for polycrystalline compounds YCo 3+ δ (−0.18≤ δ ≤0.24) and Y(Co 1− x Al x ) 2.92 ( x ≤0.1) were studied. It was found that a homogeneous rhombohedral PuNi 3 -type structure is formed within the Co concentration interval −0.14≤ δ 2.88 were determined to be 260±2 K, 0.46±0.3 μ B /Co and a =5.02 A, c =24.38 A (hexagonal set), respectively. The nonlinear variation of T C vs. Al concentration was ascribed to the composition dependence of the Co magnetic moment.

X-ray studies of magnetic phase transitions in the intermetallic compounds RMn2Ge2 (R=La, Sm, Gd, Nd, Tb, and Y)

The lattice parameters a and c of the tetragonal intermetallic compounds RMn2Ge2 (R=La, Sm, Gd, Nd, Tb, and Y) have been measured by x-ray diffraction in the temperature interval 10–800 K. Anomalies are observed in the temperature dependence of a and c due to phase transitions from the paramagnetic to the magnetically ordered state in the Mn subsystem, transitions between various magnetically ordered phases due to a change in the magnitude and sign of the Mn-Mn exchange interaction, and magnetic transitions caused by ordering of the rare-earth subsystem leading to a rearrangement of the magnetic structure of the Mn subsystem. It is concluded that, along with the lattice parameter a, the lattice parameter c also has an influence on the Mn-Mn exchange interaction.

59Co nuclear magnetic resonance in the metamagnetic system Y1−xGdxCo3

A detailed nuclear magnetic resonance (NMR) study of some intermetallic compounds of the series Y1−xGdxCo3 is presented. These are results where the NMR lines corresponding to the four magnetic sites of these compounds appear clearly resolved in the NMR spectra. We found, however, that the number of lines and their widths are strongly dependent on the radio frequency (rf) power level, which may help to explain some of the discrepancies found in NMR literature on these compounds. From the dependence of the NMR spectra with rf power we concluded that the site labeled 18h presents the largest local magnetic anisotropy. No significant changes are observed in the value of the hyperfine fields at any site as a function of the Gd concentration, x.

Influence of the f-d exchange interaction on the field-induced magnetic phase transitions in the Y1−tGdtCo3 intermetallics

A metamagnetic transition of the itinerant Co-sublattice induced by an external (t < 0.25) or an intersublattice molecular (t 0.25) field was studied in the Y 1−t Gd t Co 3 system by magnetization measurements up to 40 T. In the range 0.50 ≤ t ≤ 0.55 field-induced non-collinear magnetic structures were observed. The strength of the intersublattice molecular field is discussed

The onset of a long-range magnetic order in the spin glasses Y(Co1-xMnx)2 induced by Gd substitution

Abstract The influence of the f-d exchange interaction (induced by substitutions of Gd for Y) on the magnetic behaviour of the itinerant spin glasses Y(Co 1− x Mn x ) 2 is studied for x = 0.07 and 0.25. The substitutions give rise to a long-range ferrimagnetic order in Y 1− t Gd t (Co 1− x Mn x ) 2 systems at t ≥ 0.05 ( x = 0.25) and t ≥ 0.2 ( x = 0.07), with both f- and d-subsystems being magnetically ordered. At lower Gd concentrations the spin glass state is kept in these systems. The mean field approximation is used for analyzing the magnetization processes in compounds with homogeneously polarized d-band. The magnetization curve in effective fields up to ⋍ 1200 kOe is drawn for Y(Co 0.75 Mn 0.25 ) 2 .

The magnetic phase diagram and the effect of pressure on the magnetic properties of the intermetallic compounds

The magnetization up to 50 kOe, the magnetic susceptibility under external pressure up to 5 kbar and the thermal expansion of the cubic Laves phase compounds were studied over a wide temperature range. Two well defined concentration regions were isolated in the x-T phase diagram: , in which the antiferromagnetic structure is primarily determined by the d-d interaction (-type), and , in which the f-d interaction plays a dominant role (-type). It is concluded that both the Gd and the Mn sublattices are ordered in below , the change in the magnetic characteristics at 40 K being interpreted as an antiferromagnetism-non-collinear ferrimagnetism transition. The intermediate compound shows a freezing and time-dependent behaviour at low temperatures characteristic of short-range order. The effects can also be induced by external pressure at higher Gd concentrations.

Exchange interactions in a dinuclear manganese (II) complex with cyanopyridine-N-oxide bridging ligands

Abstract The magnetic properties of dinuclear manganese(II) complex [Mn(hfa) 2 cpo] 2 (where hfa is hexafluoroacetylacetonate anion and cpo is 4-cyanopyridine-N-oxide) are presented. The non-monotonous dependence of magnetic susceptibility is explained in terms of the hierarchy of exchange parameters by using exact diagonalization. The thermodynamic behavior of pure cpo and [Mn(hfa) 2 (cpo)] 2 is simulated numerically by an extrapolation to spin S =5/2. The Mn–Mn exchange integral is evaluated.