Ho Magnetic Moments Research Articles

Magnetic and electronic transport properties of Y- and Ho-doped La 0.9Te 0.1MnO 3

Magnetic and electronic transport properties of the electron-doped manganites La 0.9− x A x Te 0.1MnO 3 (A = Y or Ho, 0.05 ⩽ x ⩽ 0.15 ) have been investigated by measurements of magnetization, resistivity and magnetoresistance. All samples undergo a paramagnetic (PM)–ferromagnetic (FM) phase transition at Curie temperature T C and T C shifts to lower temperature with increasing Y/Ho doping level. It is very interesting to find that the values of T C and M of the Ho composition are smaller than those of the Y composition for the same concentration, although Y and Ho ions have almost the same ionic radii. Electronic transport measurements indicate that the Ho-doped compound have higher resistivity than the Y-doped one for the same doping level. These observed results are discussed according to the antiferromagnetic (AFM) coupling of the Ho magnetic moment to that of Mn.

Element-selective thermal x-ray magnetic circular dichroism study through the magnetic compensation temperature ofHo6Fe23

We present an x-ray magnetic circular dichroism (XMCD) study performed on both ${\mathrm{Ho}}_{6}{\mathrm{Fe}}_{23}$ and ${\mathrm{Y}}_{6}{\mathrm{Fe}}_{23}$ compounds as a function of the temperature. The combined analysis of both Fe $K$-edge and Ho ${L}_{2,3}$-edge XMCD spectra recorded through the magnetic compensation transition allows us to disentangle the thermal dependence of both Fe and Ho magnetic moments in ${\mathrm{Ho}}_{6}{\mathrm{Fe}}_{23}$. In addition, contributions from Ho ions to the Fe $K$-edge XMCD signals and, conversely, from Fe ions to the Ho ${L}_{2,3}$-edge XMCD spectra have been clearly identified. These extra contributions, arising from the strong $\mathrm{Fe}(3d)\text{\ensuremath{-}}\mathrm{Ho}(5d)$ hybridization, have been isolated from the spectra and correlated with the magnetic state of both Ho and Fe ions surrounding the absorbing site. The influence of these contributions to the values of the orbital and spin moments derived by using sum rule analysis is also shown.

Crystal and magnetic structure of [formula omitted

Crystal and magnetic structure and magnetic properties for deuteride HoNiSnD 0.67 are provided on the basis of high-resolution powder X-ray and neutron diffraction and magnetometric data. This deuteride crystallises with the hexagonal ZrNiAl type related structure and is antiferromagnetic below the Néel temperature equal to 2.6(3) K. The deuterium atoms occupy the tetrahedral 4h Ho 3 Ni sites. At 2 K Ho magnetic moments form a sine-modulated magnetic structure described by the propagation vector k ( = 0.34 , 0.34 , 0.117 ) . The Ho magnetic moment, equal to 5.36 μ B , lies in the basal plane (0 0 1).

Large magnetodielectric effects in orthorhombicHoMnO3andYMnO3

We have found a remarkable increase (up to 60%) of the dielectric constant with the onset of magnetic order at $42\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the metastable orthorhombic structures of $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ and $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ that proves the existence of a strong magnetodielectric coupling in the compounds. Magnetic, dielectric, and thermodynamic properties show distinct anomalies at the onset of the incommensurate magnetic order and thermal hysteresis effects are observed around the lock-in transition temperature at which the incommensurate magnetic order locks into a temperature independent wave vector. The ${\mathrm{Mn}}^{3+}$ spins and ${\mathrm{Ho}}^{3+}$ moments both contribute to the magnetodielectric coupling. A large magnetodielectric effect was observed in $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ at low temperature where the dielectric constant can be tuned by an external magnetic field resulting in a decrease of up to 8% at $7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. By comparing data for $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ and $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ the contributions to the coupling between the dielectric response and Mn and Ho magnetic moments are separated.

Magnetic Order in HoF3 Studied via Ho Nuclear Spin Probes

It is shown that in-situ 166mHo (I = 7) in a spherical single crystal of HoF3 can be used as sensitive internal thermometer to thermally detect NMR (NMR-TDNO) from the 100% abundant stable 165Ho (I = 7/2) nuclei. In addition, new 166mHo NMRON results are reported. Both the 166mHo NMRON and 165Ho NMR-TDNO spectra show three distinct quadrupolar split sub-resonances, in zero applied field. The data is used to make estimates of the Ho magnetic moments and quadrupole parameters for the 166mHo and 166mHo sites.

Magnetic ordering in HoFe0.33 Ge2

The magnetic ordering of HoFe0.33Ge2, crystallizing in the orthorhombic structure of the CeNiSi2-type has been investigated by neutron diffractometry in the temperature range between 1.6 and 15.2K. Ho magnetic moments in HoFe0.33Ge2 have been found to order antiferromagnetically below 8K. HoFe0.33Ge2 magnetic structure corresponds to propagation vector k⇒=12,12,0 and, on the basis of a group-theoretical analysis, is found to be based on the irreducible representation τ1. Also bulk magnetic measurements (susceptibility and magnetization) are reported.

Crystal and magnetic structures of RCuSb2 (R = Dy, Ho) compounds

Powder neutron diffraction measurements have been carried out on RCuSb2 (R = Dy and Ho) compounds at low temperatures. These compounds crystallize in a tetragonal ZrCuSi2-type structure and are antiferromagnets with the Néel temperatures equal to 6.4K (R = Dy) and 4.5K (R = Ho). At 1.5K the magnetic order of DyCuSb2 can be described by the propagation vector k = (0, 0.119, 0.521). At the same temperature the magnetic order in HoCuSb2 is described by three propagation vectors: k1 = (0, 0.465, 0.260), k2 = (0, 0.408, 0.770) and k3 = (0, 0, 0.519). With increasing temperature the structure described by k1 disappears about 3.5K while the two other structures described by k2 and k3 are stable up to the Néel temperature. The Dy and Ho magnetic moments form a sine-wave modulated structure in the basal plane.

Neutron scattering study of dipolar spin iceHo2Sn2O7: Frustrated pyrochlore magnet

By means of neutron scattering techniques we have investigated the frustrated pyrochlore magnet Ho_2Sn_2O_7, which was found to show a ferromagnetic spin-ice behavior below T \simeq 1.4 K by susceptibility measurements. High-resolution powder-neutron-diffraction shows no detectable disorder of the lattice, which implies appearance of a random magnetic state solely by frustrated geometry, i.e., the corner sharing tetrahedra. Magnetic inelastic-scattering spectra show that Ho magnetic moments behave as an Ising spin system at low temperatures, and that the spin fluctuation has static character. The system remains in a short-range ordered state down to T = 0.4 K. By analyzing the wave-number dependence of the magnetic scattering using a mean field theory, it is clarified that the Ising spins interact via the dipolar interaction. Therefore we conclude that Ho_2Sn_2O_7 belongs to the dipolar-spin-ice family. Slow spin dynamics is exhibited as thermal hysteresis and time dependence of the magnetic scattering.

Magnetotransport correlations in Pr- and La-based manganites

The nature of the insulating regime in certain Pr- and La-based manganites having ferromagnetic transition temperatures ( T C) close to room temperature (RT) and at T C⪡RT was studied. It is seen that in a small temperature regime close to T C and/or T P (peak resistivity temperature) the conduction mechanism is of the 3D- variable range hopping (VRH) type while far away from T P, the insulating regime is governed by an Arrhenius and/or polaronic type of behaviour. In the presence of a magnetic field the resistivity data do not fit well to either the VRH or the polaron mechanisms, however, a better fit is obtained using the magnetic localization model. Inverse ac-susceptibility ( χ′) vs temperature curves show a deviation from the Curie–Weiss behaviour at a temperature ( θ P∼paramagnetic Curie temperature) well above T C of the respective compounds, indicating the formation of superparamagnetic clusters close to RT. Our recent studies on Ho- and Y-doped manganites (La 0.7− x R x Ca 0.3MnO 3, R=Ho and Y and x=0.05, 0.075 and 0.1) unequivocally show coupling of Ho-magnetic moment with that of Mn in the lattice [Phys. Rev. B 63 (2001) 184 434].

Magnetic structure and anisotropy of YFe 6 Ga 6 and HoFe 6 Ga 6

The magnetic structure of RFe6Ga6 intermetallic compounds with R = Y, Ho have been determined by neutron powder diffraction, 57Fe Mossbauer spectroscopy, AC susceptibility, TGA (Thermo-Gravimetric Analysis) and magnetization measurements. Both compounds crystallize in the tetragonal ThMn12 structure (space group I4/mmm) with the magnetic structure of YFe6Ga6 consisting of a simple ferromagnetic alignment of Fe moments in the basal plane with a Curie temperature of 475(5) K. Gallium atoms are found to fully occupy the 8i site, with Fe and Ga atoms equally distributed over the 8j site, whilst Fe atoms fully occupy the 8f site. The average Fe moments are 1.68(10) and 1.46(10) at 15 and 293 K, respectively. The average room temperature Fe magnetic moments determined by neutron diffraction are in overall agreement with the average Fe moment deduced from Mossbauer spectroscopy and bulk magnetization measurements on this compound. The magnetic anisotropy of the compound HoFe6Ga6 is also planar in the temperature range 6-290 K, with Ho magnetic moments of 9.28(20) and 2.50(20) at 6 K and 290 K, respectively, coupled anti-ferromagnetically to the Fe sublattice and a Curie temperature of 460(10) K. The magneto-crystalline anisotropies of both compounds are comparable at low temperatures.

Magnetic structure of HoPd2Si2 redefined on the basis of newneutron diffraction data

A new sample of HoPd2Si2 (ThCr2Si2-type structure, space group I4/mmm) hasbeen prepared and investigated. Magnetic susceptibility and magnetization dataindicate antiferromagnetic behaviour below TN = 5.8 K. On the basis of powderneutron diffraction data the magnetic structure of the compound has beenredefined and found to be more complex than reported earlier. In thetemperature region from 20 K to 5 K a short-range magnetic order develops.Between 1.5 K and 5 K a long-range magnetic ordering, that could be describedin an enlarged magnetic unit cell (am = 7a, bm = a and cm = 6c), is observed.A complex magnetic structure of sine-wave modulated type with two propagationvectors and Ho magnetic moments parallel to the b-axis is proposed. Moreover,a new attempt to understand the transition from long- to short-rangemagnetic ordering observed in some rare earth compounds with Pd is made.

Neutron diffraction and Mossbauer study of the magnetic structure of HoFe/sub 6/Sn/sub 6/

We have used time-of-flight (ToF) neutron powder diffraction, and both /sup 57/Fe and /sup 119/Sn Mossbauer spectroscopy, to study the independent magnetic ordering behavior of the Fe and Ho sublattices in HoFe/sub 6/Sn/sub 6/. The crystal structure of HoFe/sub 6/Sn/sub 6/ is orthorhombic (space group Immm). The Fe sublattice orders antiferromagnetically with a Neel temperature of 559(5) K, determined by differential scanning calorimetry. The ToF neutron diffraction patterns obtained at 30 K and 295 K show that the antiferromagnetic ordering of the Fe sublattice is along [100] with a propagation vector q=[010]. The magnetic space group of the Fe sublattice is I/sub P/m'm'm' and the Fe magnetic moment at 30 K is 2.31(5) /spl mu//sub B/. This magnetic structure is confirmed by our /sup 119/Sn Mossbauer spectra in which 37% of the Sn nuclei experience a substantial transferred hyperfine field from the Fe sublattice while the remaining 63% of the Sn sites show no magnetic splitting, due to the cancellation of transferred hyperfine fields from the Fe neighbors, in full agreement with our Wigner-Seitz cell calculations for each of the eight Sn sites in the HoFe/sub 6/Sn/sub 6/ structure. The Ho sublattice orders ferromagnetically at 9(1) K, ToF data obtained at 4 K show that the Ho moments are aligned along [001], i.e. perpendicular to the Fe ordering. The magnetic space group of the Ho sublattice is Im'm'm. The refined Ho magnetic moments at 4 K are 4.4(2) /spl mu/B and 5.2(2) /spl mu/B at the 2a and 4h sites, respectively.

Magnetic properties of a HoCo 10Ti 2 single crystal

The magnetic properties of single-crystalline easy-axis ThMn 12-type ferrimagnetic HoCo 10Ti 2 have been studied. At 4.2 K, the magnetization process with the field applied along the easy c-axis is completely different from that, with the field applied perpendicular to it. The bending process of the initially antiparallel Ho and Co magnetic moments, that is observed in the latter measurement, is briefly described in terms of mean-field theory. Furthermore, when the field is applied in the hard magnetization direction, the bending process has directly been observed by means of measurement of the transversal magnetization.

Magnetotransport studies and mechanism ofHo- andY-dopedLa0.7Ca0.3MnO3

Transport properties of mixed-valence manganites of the type $({\mathrm{La}}_{0.7\ensuremath{-}x}{R}_{x}){\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ where $R=\mathrm{Ho}$ (magnetic) and Y (nonmagnetic) have been investigated above the ferromagnetic transition temperature ${(T}_{C}).$ It is interesting to see that the Ho-doped compounds have less resistivity compared to the Y-doped compounds, although Ho and Y ions have almost the same ionic radii and hence lattice strain effect would be the same in both the cases. The internal magnetic field of Ho $({\ensuremath{\mu}}_{\mathrm{eff}}^{\mathrm{Ho}}=10.5{\ensuremath{\mu}}_{B})$ is found to be responsible for this decrease in resistivity in Ho-doped compounds. Coupling of Ho magnetic moment to that of Mn has been confirmed by magnetization measurements. The resistivity data above ${T}_{C}$ fit well to the magnetic localization model proposed by Viret et al. [Phys. Rev. B 55, 8067 (1997); Phys. Rev. Lett. 75, 3910 (1995)] and the localization lengths thus obtained are reasonable. The localization lengths of the Ho-doped compounds are greater than that of Y-doped compounds of the same composition indicating that the coupling of the Ho moment with that of the Mn moments is responsible for this effect.

Specific heat and magnetocaloric effect study of multiple field-induced phase transitions inHoGa2

Both temperature and field dependences of specific heat C and magnetocaloric effect (MCE) were measured on a ${\mathrm{HoGa}}_{2}$ single crystal in fields up to 8 T at low temperatures down to 0.1 K. The magnetic fields were applied in the [100] direction, for which intermediate magnetic phases appear. Significant Ho nuclear contribution to C is found to dominate below 1 K and its field-independent character reveals that the value of Ho magnetic moments does not change visibly in the measured field range irrespective of the magnetic phases. From anomalies observed in the C and MCE data, the reported field-vs-temperature phase diagram is corroborated thermodynamically. One of the phase transitions occurring at ${T}_{t}=6.6 \mathrm{K}$ in zero field is found to be of first-order transition. Magnetic entropy determined by the MCE measurements shows an enhancement in the intermediate phases and small humps at the phase boundaries. Based on a crystalline-electric-field model, the nuclear specific heat, magnetic entropy of the $4f$ electrons, and anisotropy in the magnetization can be explained consistently. Possible origins of the reported giant magnetoresistance caused by the appearance of the intermediate phases will be discussed.

The effect of oxygen reduction on the magnetic properties of REBa 2Cu 3O 6+ x

We report on μSR measurements probing the dynamic magnetic properties of HoBa 2Cu 3O 6+ x and GdBa 2Cu 3O 6+ x powder samples with different oxygen content x. While the longitudinal field relaxation rate in GdBa 2Cu 3O 6+ x does not indicate a change of the dynamics of the Gd magnetic moments as function of oxygen content, there is a strong dependence of the dynamics of the Ho magnetic moments in HoBa 2Cu 3O 6+ x .

Breakdown of de Gennes scaling in Ho xLu 1− xNi 2B 2C

The temperature dependence of magnetic ordering and the superconducting transition have been studied for polycrystalline Ho x Lu 1− x Ni 2B 2C compounds by susceptibility and resistivity measurements as well as neutron diffraction. For Ho concentrations in the range 0⩽ x⩽0.7, the superconducting transition temperature, T c, decreases from 16.5 K at x=0 linearly with increasing x and, consequently, with increasing effective de Gennes factor. This is in accordance with a generalized Abrikosov–Gor'kov theory. At x=0.7, T c reaches 8.5 K i.e. the value of HoNi 2B 2C. Pair breaking by the Ho magnetic moments is stronger in Ho x Lu 1− x Ni 2B 2C compared to Ho x Y 1− x Ni 2B 2C. This is attributed to the difference between the lattice constants of the Ho–Y and the Ho–Lu systems resulting in different electronic structure parameters. A complete breakdown of the scaling behaviour of T c occurs for x>0.7, where T c becomes independent of the effective de Gennes factor. In this range of x re-entrant behaviour and the presence of an incommensurate a-axis, modulated antiferromagnetic structures have been observed below a characteristic temperature T m. Commensurate and incommensurate c-axis modulated antiferromagnetic structures that are observed both in the Ho–Y and the Ho–Lu systems coexist with superconductivity.

Magnetic structures of HoBdSb compound

Neutron diffraction measurements for two HoPdSb samples obtained by two different ways of preparation (samples 1 and 2) are presented. Neutron data above T N (Néel temperature) indicate that HoPdSb exists in two different crystalline phases: cubic MgAgAs-type ( F 4 3 m space group) and hexagonal LiGeGa-type ( P 6 3 mc space group). The weight percentages of these two phases are 75%-cubic, 25%-hexagonal for sample 1, 3%-cubic, 97%-hexagonal for sample 2. At low temperatures, the Ho magnetic moments in HoPdSb are ordered, whatever the crystal structure. For cubic HoPdSb, below T N = 2.7(2) K, a MnO-type antiferromagnetic structure is obtained, with Ho magnetic moments perpendicular to [1 1 1] direction and equal to 4.50(5) μ B at 1.5 K. For hexagonal HoPdSb, below T N = 3.8(2) K, a collinear antiferromagnetic structure is obtained, with propagation vector k = ( 1 2 0 0) , Ho magnetic moments parallel to c -axis and equal to 2.05(5) μ B at T = 1.5 K.

Neutron powder diffraction study of the nuclear and magnetic structures of HoNi 1.985Co 0.015B 2C and HoNiBC

The nuclear and magnetic structures of HoNi 1.985Co 0.015B 2C and HoNiBC have been analyzed by neutron powder methods. The first of these materials crystallizes with the symmetry of space group I4/mmm, lattice parameters (at room temperature) a = 3.52011(9), c = 10.5286(3) A ̊ , and is isostructrural with the undoped compound HoNi 2B 2C. Cobalt and nickel atoms are disordered over the same crystallographic sites. Well below the Neèl temperature (∼ 8 K), the magnetic moments of the Ho atoms are ordered ferromagnetically in the a, b planes and antiferromagnetically along the c-axis, with a magnitude of the moment of 8.26(6) μ B. The Co doping, even at such low concentrations, destroys the superconducting behavior of the undoped phase. The compound HoNiBC is also tetragonal (space group P4/nmm), with lattice parameters (at room temperature) a = 3.5631(2), c = 7.5486(6) A ̊ , and is isostructural with LuNiBC. Below the Neèl temperature (9.82(8) K), the Ho magnetic moments are ordered ferromagnetically in the bi-layers (HoC)(HoC) with spins lying in the a, b planes, and successive bi-layers are ordered antiferromagnetically along the c-axis. The magnitude of the moments is 6.74(9) μ B. No structural distortions associated with the magnetic ordering were observed in either compound.

The μSR study of the relaxation of Ho and Er magnetic moments in high-Tc 1-2-3 compounds

High temperature superconductors HoBa2Cu3O7−δ (T c ≅93 K), Ho0.5Y0.5Ba2Cu3O7−δ (T c ≅93 K) and ErBa2Cu3O7−δ (T c ≅95 K) were investigated by the zero-field μSR-technique. The muon spin depolarisation rate connected with the fluctuation frequency of rare-earth ion magnetic moments was measured. It was found that the samples with holmium show a fast increase of the muon spin depolarisation rate at temperatures below 20 K, while in ErBa2Cu3O7−δ the depolarisation rate remains low in the whole temperature region studied (4.2 K-270 K). The sharp difference between the behaviours of the muon spin depolarisation rate may be explained by the difference between the ground state of Ho3+ and Er3+ ions in the crystalline field of the lattice.