Bulk Magnetization Measurements Research Articles

Influence of the Cr 5+ ion on the magnetic properties of YbCrO 4 oxide

The magnetic properties of the YbCrO 4 oxide have been studied by both bulk magnetic measurements and 170Yb Mössbauer spectroscopy. Ferrimagnetic ordering is shown to be present below 25 K, driven by the exchange within the chromium sublattice. In the saturation state, the magnetic moment is 0.55 μ B for Yb 3+, and presumably 1 μ B for Cr 5+, the two sublattices being antiferromagnetically coupled. The anisotropic Yb–Cr exchange polarises the Yb 3+ sublattice below 25 K, so as to force the Yb magnetic moments to lie in the hard magnetic a– b plane.

Interplay between Tm 3+ and Cr 5+ magnetic sublattices in TmCrO 4

The compound TmCrO 4 has been studied with bulk magnetization measurements, 169 Tm Mössbauer spectroscopy and muon spin relaxation (μSR). The Cr sublattice in TmCrO 4, which orders with a second-order magnetic phase transition at T C =18.75 K , gradually induces magnetic order in the non-magnetic crystal field ground state of the Tm sublattice.

Magnetic properties of RNi 1− xIn 1+ x (R=Gd–Er) compounds

AC and DC bulk magnetic measurements were performed for RNi 1− x In 1+ x (R=Gd–Er and x=0,0.1, 0.25) compounds. These compounds crystallize in the hexagonal ZrNiAl-type structure. The lattice parameters a and c for the RNiIn series decrease linearly with increasing number of 4f electrons. For nonstoichiometric RNi 1− x In 1+ x additional indium atoms occupy the 2(c) crystallographic site and the a parameter increases while the c parameter decreases with increasing indium content. The stoichiometric samples show ferromagnetic behavior with the critical temperature changing from 96 K for R=Gd to 9 K for R=Er. In the nonstoichiometric RNi 1− x In 1+ x compounds increase in the indium content leads to decrease in the ferromagnetic critical temperatures and to a change of the antiferromagnetic ordering for x=0.25 in the case of R=Dy, Ho and Er.

Magnetic alignment in nominally non-magnetic hexagonal metal hydrides: NMR

Powders of three hexagonal metal-hydrides or -deuterides are found to align in 4.4– 8.3 T magnetic fields used for NMR. The field-alignment is unexpected, since all three systems have very small susceptibilities, as demonstrated by sharp NMR lines. The extent of alignment runs from nearly complete to barely detectable in ZrBe 2(H,D) x , LuD 3, and YD 3, respectively. The preferred alignment direction in ZrBe 2(H,D) x is with the crystallites’ c-axis perpendicular to B, while the c-axis and B tend to be parallel in LuD 3 and YD 3. The susceptibilities χ || and χ ⊥ are determined from bulk magnetization measurements in aligned ZrBe 2H 1.4 powder. The alignment must be considered for proper analysis of NMR spectra in these and related materials.

The interplay of the crystalline electric field and quadrupolarinteractions in the spontaneous magnetic phases of DyIn3

DyIn3orders at TN = 20 Kand undergoes a second spontaneous magnetic transition at16.5 K. From bulk magnetization measurements, performed on asingle crystal along the three main axes of the cubic AuCu3-typestructure, the magnetic phase diagrams have been established. The crystallineelectric field (CEF) scheme, in the paramagnetic phase, and the magneticstructures of the spontaneous and low field-induced phases have been probed byneutron techniques. All the magnetic phases studied are found to be multipleq withqbelonging to the ⟨1/2, 1/2, 0⟩star. In the low temperature phase (T < 16.5 K) the structureis double qwith moments along twofold axes, whereas above 16.5 K it becomes tripleqwith moments along threefold axes. The analysis of the experimentalresults within the periodic molecular field model leads to a coherentinterpretation of the spontaneous magnetic transitions, mainly drivenby bilinear exchange and CEF interactions. Though the existence ofquadrupolar interactions is definitively proved by the stabilization of multipleqmagnetic structures, quadrupolar coefficients are found to be one orderof magnitude smaller than those previously reported for NdIn3 andTbIn3.

A Systematic Exploration of Nickel–Pyrazolinato Chemistry with Alkali Metals: New Cages From Serendipitous Assembly

AbstractThe preparation and properties of fourteen novel paramagnetic [NiIIx] aggregates bridged by pivalate, pyrazolinolate and in most cases hydroxide are reported. A rich structural diversity has been achieved by changing the nature of the alkali of the base used during the synthesis, leading to the nuclearities [NiII4NaI4] (2, 3, 4), [NiII5NaI4] (5, 6, 7), [NiII5LiI6] (8), [NiII8MI2] (M=K (9, 10), Rb (11, 12), Cs (13, 14) and [NiII8] (15). All compounds have been characterised by single‐crystal Xray diffraction; however, full crystallographic details are given only for the representative molecules [Ni4Na4(fpo)4(piv)8(Hpiv)8] (2), [Ni5Na4(OH)2(mpo)4(piv)8(Hpiv)2(MeCN)2] (5), [Ni5Li6(OH)2(fpo)2(piv)12(Hpiv)4] (8), [Ni8K2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (9), [Ni8Rb2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (11), [Ni8Cs2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (13) and [Ni8(OH)4(mpo)2(PhCH2CO2)10(Hmpo)8] (15). Variable‐temperature bulk magnetisation measurements have been performed for each type of complex. The [NiII4NaI4] clusters show intramolecular antiferromagnetic coupling and a spin ground state of S=0. Complexes of the type [NiII5NaI4] also display antiferromagnetic superexchange, leading to an S=1 spin ground state. The molecule with nuclearity [NiII5LiI6], in contrast, exhibits ferromagnetic interactions, resulting in the presence of low energy states with high multiplicity, and a spin ground state S&gt;1. The [NiII8MI2] and [NiII8] clusters have the same topology of spin carriers, which display predominantly antiferromagnetic interactions to yield a diamagnetic ground state. The coupling within these octanuclear NiII clusters is rationalised in terms of the nature of the Ni‐O‐Ni angles within the core.

Magnetization reversal of individual Fe nanowires in alumites studied by magnetic force microscopy

We have studied the magnetization reversal of two-dimensional (2D) arrays of parallel ferromagnetic Fe nanowires in nanoporous alumina templates. Combining bulk magnetization measurements using a superconducting quantum interference device with field-dependent magnetic force microscopy (MFM), we decomposed the macroscopic hysteresis loop in terms of irreversible magnetic responses of individual nanowires. The field-dependent MFM provides a microscopic method by which to obtain the hysteresis curve by registering the fraction of upward and downward magnetized wires for each field. The nanowire system proves to be an excellent example of the 2D classical Preisach model, well-known from the field of hysteresis modeling and micromagnetism.

Magnetic phase transitions in TbRhSn

The magnetic ordering of TbRhSn, crystallizing in the hexagonal ZrNiAl-type structure, has been investigated by high-resolution neutron diffractometry in the temperature range between 1.7 and 23.9K. Tb in TbRhSn has been found to order magnetically below 19K. Its magnetic structure corresponds to propagation vector k→=[12,0,12], and by a new group-theoretical analysis is shown to be based on the two irreducible representations τ2 and τ4. This model also explains the change of magnetic ordering at Tt=11K. New aspects of bulk magnetic measurements are also reported. Moreover, our results are compared with previously published data.

Element-Specified Observation of Surface-Influenced Magnetization Process in Gd/Fe Multilayer

Element-specific magnetic field hysteresis on a Fe(20 A)/[Gd(30 A)/Fe(20 A)] × 50 multilayer has been measured by means of X-ray magnetic circular dichroism at Gd- L 3 and Fe- K edges at 16 K, 195 K and 300 K, together with bulk magnetization measurements. These results are examined on the basis of Camley's model, which describes the multilayer as a one-dimensional spin chain. At 195 K, which is near the compensation temperature, the observed hysteresis curve is interpreted as a series of magnetic states: canted Fe-aligned, surface-twisted, and Fe-dominant bulk-twisted states. These unique spin configurations are promoted by the surface magnetization of outermost Fe slabs and the exchange-spring-like behavior within Gd slabs.

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

The magnetization reversal of two-dimensional arrays of parallel ferromagnetic Fe nanowires embedded in nanoporous alumina templates has been studied. By combining bulk magnetization measurements (superconducting quantum interference device magnetometry) with field-dependent magnetic force microscopy (MFM), we have been able to decompose the macroscopic hysteresis loop in terms of the irreversible magnetic responses of individual nanowires. The latter are found to behave as monodomain ferromagnetic needles, with hysteresis loops displaced (asymmetric) as a consequence of the strong dipolar interactions between them. The application of field-dependent MFM provides a microscopic method to obtain the hysteresis curve of the array, by simply registering the fraction of up and down magnetized wires as a function of applied field. The observed deviations from the rectangular shape of the macroscopic hysteresis loop of the array can be ascribed to the spatial variation of the dipolar field through the inhomogeneously filled membrane. The system studied proves to be an excellent example of the two-dimensional classical Preisach model, well known from the field of hysteresis modeling and micromagnetism.

Spin-gap and antiferromagnetic correlations in low-dimensional PbNi 2-x A x V 2 O 8 compounds (A=Mg, Co)

The effect of the impurity doping in the quantum-spin chains of the PbNi2V2O8 Haldane-gap compound is studied. We report elastic neutron scattering and bulk magnetic susceptibility measurements on the quasi-one-dimensional system PbNi2-xAxV2O8 doped at the Ni2+ (S=1) sites by either non-magnetic A=Mg2+ (S=0) or magnetic A=Co2+ (S=3/2) ions, with x=0.12 and 0.08, respectively. The results reveal that the magnitude of the Neel temperature depends strongly on the spin value of the A cation.

Neutron-scattering studies of the S = 2 antiferromagnetic chain MnCl 3 (C 10 D 8 N 2 )

Quasi-elastic and inelastic neutron scattering studies of the quasi-one-dimensional S=2 antiferromagnet MnCl3(C10D8N2) are reported. The quasi-elastic measurements exhibit a broad peak at Q≈0.69 A-1, which is consistent with short-range antiferromagnetic coupling between neighboring Mn3+ ions. Inelastic experiments, at 150 mK and Q=0.70 A-1, reveal decreased magnetic scattering at energies less than 0.2 meV when compared to similar studies at 20 K. These results provide microscopic evidence for the presence of a Haldane gap and are consistent with the bulk magnetization measurements of Granroth et al.

XMCD Characterization of the Ferromagnetic State of Yb14MnSb11.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effect of included guest molecules on the normal state conductivity and superconductivity of beta''-(ET)(4)[(H(3)O)Ga(C(2)O(4))(3)].G (G = pyridine, nitrobenzene).

Normal state conductivity and superconductivity together with bulk magnetic susceptibility and magnetization measurements have been measured for two molecular charge-transfer salts: beta' '-(ET)4[(H3O)Ga(C2O4)3]G (ET = bis(ethylenedithio)tetrathiafulvalene, G = pyridine for compound I and nitrobenzene for compound II). With the exception of the included guest molecules (G) the crystal structures are almost identical. Both show minima in their electrical transport at 130 K for I and at 160 K for II, but at lower temperatures their behaviors differ markedly. The resistance of I reaches a maximum at 50 K with a further small peak at 2 K and possible superconductivity only below 2 K, whereas that of II increases continuously down to 7.5 K, where an abrupt transition to a superconducting state occurs.

XMCD characterization of the ferromagnetic state of Yb14MnSb11.

X-ray magnetic circular dichroism (XMCD) measurements on Yb14MnSb11 provide experimental evidence of a moment of 5 microB on Mn, with partial cancellation by an opposing moment on the Sb4 cage surrounding each Mn ion. The compound is isostructural to Ca14AlSb11, with Mn occupying the Al site in the AlSb4(9-) discrete tetrahedral, anionic unit. Bulk magnetization measurements indicate a saturation moment of 3.90 +/- 0.02 microB/formula unit consistent with four unpaired spins and implying a Mn3+, high-spin d4 state. XMCD measurements reveal that there is strong dichroism in the Mn L23 edge, the Sb M45 edge shows a weak dichroism indicating antialignment to the Mn, and the Yb N45 edge shows no dichroism. Comparisons of the Mn spectra with theoretical models for Mn2+ show excellent agreement. The bulk magnetization can be understood as Mn with a moment of 5 microB and a 2+ configuration, with cancellation of one spin by an antialigned moment from the Sb 5p band of the Sb4 cage surrounding the Mn.

Magnetic properties of CeFeSi-type RTiSi compounds (R=Gd–Tm, Lu, Y) from magnetic measurements and neutron diffraction

Numerous solid-state syntheses clearly show that the CeFeSi-type (P4/nmm) RTiSi series is limited to the heaviest rare-earth elements (R=Gd–Tm, Lu, Y). Bulk magnetisation and neutron diffraction measurements have been performed on these compounds. YTiSi and LuTiSi are Pauli paramagnets whereas the R(=Gd–Tm)TiSi compounds behave antiferromagnetically below 400, 288, 175, 98, 51 and 20 K, respectively. The magnetic structure of the (Tb–Er)TiSi compounds consists of ferromagnetic (0 0 1) R layers antiferromagnetically coupled along the c-axis with the (++−−) coupling sequence. The three first compounds exhibit an easy-axis anisotropy whereas an easy plane prevails in ErTiSi. In all cases, the R moment value is close to the R 3+ value (gJ). The results are compared with those obtained on the corresponding RTiGe germanides.

Neutron Scattering on Magnetic Materials Under Extreme Conditions

Many materials exhibit various magnetic phenomena as a function of magnetic field, temperature and/or pressure. Usually, bulk magnetic measurements provide first information on the magnetic state of the material by measuring their response on the applied magnetic field. However, it is necessary to investigate materials also on a microscopic scale. This is often done by means of neutron scattering. In this contribution we discuss basic ideas of this method and we report on few experimental results obtained with a split-pair coil 14.5 T superconducting magnet which can be combined with dilution stick offering temperatures as low as 30 mK and/or with a small clamped-type pressure cell which offers pressure up to 1.0 GPa.

11BNMR detection of the magnetic field distribution in the mixed superconducting state ofMgB2

The temperature dependence of the magnetic field distribution in the mixed superconducting phase of randomly oriented MgB$_2$ powder was probed by $% ^{11}$B NMR spectroscopy. Below the temperature of the second critical ($B_{% {c2}}$) field, $T_{{c2}}\approx 27$K, our spectra reveal two NMR signal components, one mapping the magnetic field distribution in the mixed superconducting state and the other one arising from the normal state. The complementary use of bulk magnetization and NMR measurements reveals that MgB$_2$ is an anisotropic superconductor with a $B_{c2}^c<2.35$ Tesla anisotropy parameter $\gamma\approx 6$.

Simultaneous structural and magnetic transitions in YFe 4Ge 2 studied by neutron diffraction and magnetic measurements

The magnetic behaviour of the tetragonal YFe 4Ge 2 compound has been studied by neutron diffraction and bulk magnetisation measurements. Magnetic ordering occurs below T N =43.5 K simultaneously with a structural transition from tetragonal P4 2/mnm→Pnnm to orthorhombic symmetry. Both transitions are of first order. The symmetry breaking is connected with primary displacive order parameters involving shifts of the Fe atoms. The Fe site splits into two sites in Pnnm, the shifts of the Fe atoms with respect to the tetragonal phase have opposite signs along the a (dilatation) and b (contraction) axes. This induces the symmetry breaking tensile strains. The planar canted antiferromagnetic arrangement with eight sublattices is the ground state associated with a magnetic energy involving isotropic exchange and anisotropic (relativistic) interactions. The magnetic structure is invariant under the magnetic space group P 2 1 n′ 2 1 n′ 2 1 m′ ( Sh 58 399) . The moments of the two orbits have the same value. At 1.5 K the Fe moment equals 0.63(4) μ B/Fe atom. The YFe 4Ge 2 magnetostructural phenomena are compared to the more complex analogue of the ErFe 4Ge 2 compound. The structural and magnetic transitions are described phenomenologically within a Landau–Dzialoshinski approach which assumes a triggering mechanism, in which the spontaneous strain is triggered by the exchange contribution to the magnetic ordering.

Magneto-optical investigation of flux penetration in a superconducting ring

Using advanced magneto-optics, the field and current distributions in superconducting thin film ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ rings in an externally applied magnetic field are studied experimentally. The observations are in close agreement with numerical calculations. During the initial flux penetration and field reversal a highly nonuniform current distribution is observed. In particular, concentric counterrotating current loops occur during field reversal. We explore implications of these results for the determination of critical currents and penetration fields from bulk magnetization measurements.