Andrzej W. Pacyna

Crystal and magnetic properties of GdTSn compounds (T = Ag, Au)

Abstract The results of structure, ac and dc susceptibilities, and 119 Sn Mossbauer studies of GdAgSn and GdAuSn compounds are presented. It was found that these compounds order anti-ferromagnetically at T N = 34.3(2) K, and T n = 22.9(2) K, respectively. Additionally a second transition at T f = 15.3(2) K was discovered for both intermetallics. The nature of this second transition is discussed and strong experimental arguments supporting the spin-glass origin and reentrant antiferromagnetic character of the compounds under study are given.

Structure, magnetic properties and {sup 119}Sn Mossbauer spectroscopy of PrRhSn

AbstractPrRhSnwassynthesizedinpolycrystallineformbyareactionofpraseodymium,rhodium,andtininanarc-meltingfurnace.Thesample was investigated by powder and single crystal X-ray diffraction: ZrNiAl type, space group P¯62 m; a ¼ 742:49ð7Þ,c ¼ 415:05ð5Þpm, wR 2 ¼ 0.0737, 353F 2 values and 14 variables. The PrRhSn structure has two crystallographically independentrhodiumsiteswithatricappedtrigonalprismaticcoordination,i.e.[Rh1Sn 3 Pr 6 ]and[Rh2Sn 6 Pr 3 ].Therhodiumandtinatomsbuildup a three-dimensional [RhSn] network with short Rh–Sn contacts (278 and 285pm), in which the praseodymium atoms filldistorted hexagonal channels. The magnetic and electronic properties of PrRhSn have been studied by means of AC and DCmagnetic susceptibility measurements as well as 119 Sn Mo¨ssbauer spectroscopy. A transition from a paramagnetic to aferromagneticstatewasfoundatT C ¼ 3:0K.r 2005ElsevierInc.Allrightsreserved. Keywords: Intermetalliccompound;Magnetism;Mo¨ssbauerspectroscopy 1. IntroductionThe rare-earth metal based stannides RERhSn(RE ¼ rare-earthelement)havethoroughlybeeninves-tigated in recent years [1–5, and references therein].A detailed literature overview is given in [1] and [5].Especially, the valence fluctuations of CeRhSn andthe heavy fermion behavior of YbRhSn are of greatinterest.The crystal chemistry and the physical propertiesof the RERhSn stannides with the early rare-earthelementshavecontroversiallybeendiscussed.ThelatticeparametersforCeRhSn,PrRhSn,andNdRhSnreportedbyRoutsietal.[6]aredifferentfromthosereportedbyMishra et al. [1]. A recent single crystal study of theNdRhSnstructure[7]clearlyconfirmedtheX-raypowderdatagivenin[1].Thetwodifferentstudiesalsorevealedadiscrepancyconcerningthemagneticordering.Whilenohint for magnetic ordering was evident in the originalwork [6], ferromagnetic ordering at T

Solid solutions TbFe1−xAlxO3 (0 ⩽ x ⩽ 1): Structure and magnetic behaviour☆

Abstract Magnetic X-ray, neutron diffraction and DSC measurements for a solid solution of the TbFe 1− x Al x O 3 system have been carried out. The results obtained indicate an essential role for Al substitutions on the magnetic behaviour of the compounds examined. For low Al concentration, a radical reduction of magnetic susceptibility of the compounds has been observed. The increase in Al concentration ( x = 0.4−0.7) generates a compensation temperature (∼35 K) in the system. This effect is responsible for the change in the type of Tb-Fe coupling (from ferromagnetic to antiferromagnetic).

Influence of Temperature Independent Contribution of Magnetic Susceptibility on the Curie-Weiss Law

A fitting procedure of the Curie-Weiss law, eliminating the temperature independent contribution (0) from the experimental susceptibility data, was used for determination of the magnetic parameters, i.e. a Curie constant, a Curie-Weiss temperature and an effective magnetic moment, because the theoretical considerations showed that the Curie-Weiss law is invalid for 0  0, even small. This method revealed for the HgCo(NCS)4 paramagnet, commonly accepted as a magnetic susceptibility standard, 0 = 2.43710-6 cm3/g, while for the ZnCr2Se4 antiferromagnet, known as a matrix of various diluted systems, – 0 = -2.56610-6 cm3/g, for comparison.

Magnetic susceptibility of powder and single-crystal TmFeO3 orthoferrite

Abstract This paper presents the results of magnetic susceptibility investigations carried out on TmFeO 3 samples, both single crystal and powder. It is shown that powder specimens exhibit a pronounced magnetic thermoremanence effect. This effect can be employed to determine phase transition temperatures from susceptibility measurements performed on polycrystalline substances. Until now, these temperatures had been obtained only from examining the spontaneous magnetisation of single-crystal specimens. The spin reorientation temperatures obtained from various measurements are compared.

Double exchange magnetic interaction and giant negative magnetoresistivity in the spin glass state of the new compound CuCr1.6Sb0.4S4

Abstract CuCr 1.6 Sb 0.4 S 4 crystallizes in the spinel structure with the lattice parameter a =9.9680(1) A and the anion parameter u =0.3820(1). The very hard magnetization of the sample, the shape of the magnetization isotherms as well as the lack of magnetic saturation even in a field of B =14 T indicate that the antiferromagnetic superexchange interaction dominates the long-range magnetic interactions between the magnetic moments localized on the chromium ions. A high positive value of the paramagnetic Curie–Weiss temperature Θ C–W (equal to 318 K) testifies that the short-range interaction is ferromagnetic and strong which means that in the corresponding microregions the double exchange interaction is present and predominates. A suggestion is made that these microregions behave like superparamagnetic clusters. As the result of the competition of the interactions mentioned above the sample under study reveals a spin glass state at low temperatures, which is confirmed by the temperature dependence of the magnetic susceptibility curves. The spin-freezing temperature is lower than 50 K. CuCr 1.6 Sb 0.4 S 4 is a semiconductor with a giant negative magnetoresistivity equal to 74% at 38 T and 3 K. The driving force of this effect is the double exchange magnetic interaction. Three values for the activation energy were observed: E 1 =0.118 eV, E 2 =0.004 eV and E 3 =0.033 eV. These are most probably connected with the energy levels generated by the crystal field.

Magnetic behaviour of TmFe1−xAlxO3 system (x≤0.1)

Magnetisation measurements for some representatives of TmFe 1−x Al x O 3 system were performed. Singularities on the experimental curves mark some phase transition points of the investigated substances. The obtained results indicate an essential influence of Al substitution on magnetic behaviour of examined compounds: a rise in T c and T t1 , T t2 , compensation and spin reorientation process temperatures respectively, as well as broadening of the temperature range of reorientation process

Crystal and magnetic structure of TbNiGe and DyNiGe compounds

Abstract The results of X-ray neutron diffraction and magnetometric measurements for TbNiGe and DyNiGe compounds are presented. Both compounds crystallize in an orthorhombic TiNiSi-type crystal structure and are antiferromagnets with Neel temperature of 18 and 6 K, respectively. At low temperatures both compounds have square modulated structures with a wave vector k = ( 2 3 , 1 3 , 0) . With increase in temperature a change to a sinusoidally modulated structure for TbNiGe and probably a cycloidal spiral structure for DyNiGe is observed. In both structures and both phases the magnetic moments are parallel to the c -axis. In the case of the TbNiGe compound a coexistence of two magnetic structures over a wide temperature range is observed. The experimentally determined magnetic structures are in agreement with those proposed by symmetry analysis.

Magnetic superexchange interactions and metamagnetic phase transitions in the single crystals of the spinels ZnCr2−xInxSe4 (0 ≤ x ≤ 0.14)

Abstract The experimental data for the magnetization and the magnetic susceptibility, as well as their dependence on temperature, on the induction of the external magnetic field and on the concentration x have been analyzed. The metamagnetic phase transitions induced by the external magnetic field have been observed as plateau areas and jump-like increments on the magnetization curves at 4.2 K. High values of the effective magnetic moment μ eff and of the Curie constant C M point to the existence of Cr 2+ ions as well as Cr 3+ ions. The exchange constants, transfer integrals and the spiral angles for the solid solutions under study have been evaluated.

AC susceptibility of TmFeO3 single-crystal

Abstract This paper presents the results of AC-susceptibility measurements performed on TmFeO 3 single-crystal orthoferrite. The AC-measurements were carried out without any static magnetic field ( H 0 =0) but for different frequencies and amplitudes of the oscillating field. It is shown that singularities of both (in-phase and out-of-phase) AC-susceptibility components closely correlate with phase transitions in TmFeO 3 . From the dynamic susceptibility temperature dependence some information about magnetic domain and system non-linearity can be derived.