Exchange energy for conduction electrons in (ZnMn)Se derived from spin-flip Raman scattering and magnetization

Spin-flip Raman scattering, magnetization, and susceptibility data for Zn_0.97Mn_0.03Se are reported. The exchange energy N_oα = 243 ± 10 meV for the conduction electrons is obtained from an analysis of the Raman and magnetization data. At large magnetic fields (H > 60 kOe), the spin-flip energy ΔE saturates at 14 meV. At low fields ΔE does not extrapolate to zero as H → 0, which is characteristic of scattering from donor-bound electrons. The low temperature magnetization curves are fit to a modified Brillouin function. The fit gives $\text{x}\text{?}\text{/x}\text{= 0.67}$ as the fraction of active magnetic ions, and an effective temperature T_eff = T + T_o with T_o = 1.1 K. The magnetic susceptibility follows a Curie-Weiss law between T = 150 and 280 K with a Curie-Weiss temperature θ = ?33 K.     

Analysis of the high-temperature spin-glass susceptibility: Determination of the local magnetic exchange

New measurements are reported of the magnetic susceptibility above the freezing temperature T_f for noble-metal spin-glasses with $\text{1}\text{2}$ to 6 at.% Fe or Mn. The susceptibility for T_f<T?5 T_f is not Curie-Weiss, but local magnetic correlations manifest themselves and provide a key for the determination of the exchange interactions in spin-glasses. The exchange parameters J_n are resolved up to 5 neighbors for $\text{Au}$Fe, $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Pt}$Mn through a configuration ensemble calculation which includes atomic short range order.     

Thermal and magnetic studies of the nearly one-dimensional antiferromagnetic system CsNiBr3

Magnetic susceptibility, specific heat and ¹³³Cs magnetic resonance measurements in a single crystal of CsNiBr₃ are reported. The data reveal two magnetic transitions separating the paramagnetic phase from the antiferromagnetic ground state. At the higher transition temperature T_N2 = (14.25 ± 0.05)K a net magnetic moment is observed only along the hexagonal c-axis, while only below the lower transition temperature T_N1 = (11.75 ± 0.05)K a perpendicular component of the magnetic moment appears also. Above T_N2 CsNiBr₃ can be described as a one-dimensional antiferromagnet with intrachain exchange interaction $\text{J}\text{k}{}_{\mathrm{B}}\text{= ?(17.0 ± 0.2)}\text{K}$ and single-ion anisotropy constant $\text{D}\text{k}{}_{\mathrm{B}}\text{? ?1.5}\text{K}$. Below T_N1, the data are consistent with the non-colinear triangular structure of the Ni²⁺ moments proposed previously for the isomorphic crystal CsNiCl₃. A reduced value of the zero-temperature susceptibility over the classical value is found and atrributed to the zero point deviations.     

Compensation effect in an exchange enhanced superconductor: [(La.993Lu.007)1−xGdx]Ru2

We have measured the upper critical field, H_c2, of alloys of the form [(La_.993Lu_.007)_1?xGd_x]Ru₂. For large $\text{(x?0.02)}$ concentrations of Gd, the critical fields are re-entrant. For small (x?0.01) concentrations of Gd, the critical fields cross the pure sample critical fields and rise above them due to compensation of the externally applied magnetic field by the negative effective internal field of the magnetic impurity. Compensation occurs at relatively low fields (25 KG) in this system as a result of substantial exchange enhancement. From the concentration and critical field of the most compensated sample, we find a value for the exchange integral, J(0) = ?(15+?2) meV, and a susceptibility enhancement factor in excellent agreement with EPR, specific heat and static susceptibility measurements.     

One-dimensional magnetism in N2H6FeF5,

A new Fe(III) fluoride N₂H₆FeF₅ has been investigated by magnetic susceptibility measurements and Mössbauer resonance. It has a one-dimensional magnetic behaviour. The intrachain exchange integral ($\text{J}\text{k}\text{= -10.2}\text{K}$) has been determined by fitting the χ^-1 = f(T) curve and the ratio between the inter- and intrachain exchange integrals evaluated with Oguchi's formula. Below T_N = 9 K, N₂H₆FeF₅ shows a long range three-dimensional anti-ferromagnetic ordering.     

Raman scattering in magnetic US3

A Raman scattering investigation of magnetic US₃ has been made from 7 to 300 K. Comparison of room temperature spectra with those of the non magnetic isostructural sulfide HfS₃ allowed the assignment of most of the lines to $\textcolor{red}{}\text{=}\text{0}$ optical phonons. Drastic changes take place in the 10?150 cm^?1 range when lowering the temperature down to 7 K : four equally spaced lines appear at 54, 72.5, 91 and 109.5 cm^?1. Three of them broaden significantly with increasing temperature and disappear near 50 K, at which previous measurements indicate a maximum in the magnetic susceptibility and suggest a magnetic phase transition. The stronger fourth line is still observed at 100 K and merges into a phonon line at higher temperature. These four lines are attributed to electronic transitions within the 5f² configuration of U⁴⁺. Their temperature dependences appear to involve a spin-dependent scattering mechanism and are consistent with antiferromagnetic ordering.     

Critical behaviour of a uniaxial ferromagnet,ErCl3·6H2O with predominant dipolar interactions

The parallel magnetic susceptibility χ of a uniaxial ferromagnet ErCl₃·6H₂O has been measured between 0.3 and 4.2K and specially near T_c = 0.353 K. The predominant contribution to the Curie-Weiss temperature is due to the dipolar interactions. χ is proportional to ?^?γ with $\text{? =}\text{T}\text{T}{}_{\mathrm{c}}\text{?1}$ in the range 10^?3 < ? < 5 × 10^?2. The γ value, γ = 1.01 ±0.03 is consistent with the theoretical prediction for a uniaxial dipolar ferromagnet.     

Reentrant superconductivity in the orthorhombic system (Tm1−xLux)RuB2

The boundaries between the paramagnetic, superconducting and magnetically ordered phases in the orthorhombic pseudoternary system (Tm_1?xLu_x)RuB₂ have been established by means of ac magnetic susceptibility measurements down to 1.2 K. Reentrant superconductivity occurs between x = 0.52 and x ? 0.68. The absence of coexistence between superconductivity and long range magnetic order in this region suggests a ferromagnetic-like nature of the magnetic state. The initial linear depression of superconducting transition temperature (T_c) gives a coupling constant value N(E_F)$\text{J}$² between conduction electrons and magnetic Tm³⁺ moments of 6.7 × 10^?4 eV-atom-states/ spin direction.     

Magnetic phase transitions,anisotropic susceptibility and dipolar interactions in antiferromagnetic MnNb2O6

The magnetic properties of MnNb₂O₆ single crystals have been studied in the temperature range 1.6–300 K (T_N = 4.4 K), in fields up to 220 kOe. The high field saturation at low temperature, as well as the paramagnetic susceptibility at high temperature, agree well with a ${}^6\text{S}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ state for Mn²⁺ ions. From 1.6 to 3.8 K a spin flop is induced by fields ranging from 17 to 21 kOe, applied in the direction of the a-axis. Elements of the magnetic susceptibility tensors up to rank 12, measured below the spin flop field, are in accordance with a magnetic anisotropy originating mainly from magnetic dipolar interactions.     

Magnetic properties of CuCr2Se4 single crystals

The magnetic properties of CuCr₂Se₄ single crystals, which were grown by chemical transport reactions using iodine as a carrier, have been investigated. The magnetic moment at 0 K is found to be 5.07 μ_B per mole. The susceptibility at high temperatures follows a Curie-Weiss law with an asymptotic Curie temperature 430 K and a Curie constant 2.55 emu · $\text{deg}\text{mol}$. The magnetocrystalline anisotropy constants K₁ and K₂ are ? 6.9x 10⁵ and ? 0.9x 10⁵$\text{erg}\text{cm}{}^3$, respectively, at 5.1 K.In order to examine the effects of annealing on the magnetocrystalline anisotropy, the ferromagnetic resonance at room temperature was measured after annealing in vacuum and subsequently in an atmosphere of Se. It is found that the absolute values of K₁ and K₂ decrease after annealing in vacuum and increase to the initial values after annealing in an atmosphere of Se.     

Magnetic properties of n-type CuInS2

The magnetic susceptibility, χ, of a polycrystalline n-type CuInS₂ sample has been measured in the temperature range 4.2–300 K. A shallow donor level at 0.017 eV has been identified and an antiferromagnetic exchange coupling between donors is observed. These results are inferred from the excellent fit of the data to the equation $\text{χ(10}{}^{\mathrm{?6}}\text{cm}{}^3\text{mole}{}^{\mathrm{?1}}\text{) = -83.7 + 185}\text{[1?exp (}\text{?100}\text{T}\text{)]}\text{(T + 3)}$ in the whole temperature range.     

Magnetic heat capacity of an amorphous Gd-Al alloy

The magnetic specific heat of amorphous GdAl₂ shows a broad maximum near 17.5 K, the temperature of the spin-glass-like cusp in the magnetic susceptibility. At low temperatures it varies as $\text{T}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, with a small negative intercept. This is interpreted in terms of ferromagnetic spin waves excited in regions some 35 Å in size.     

The Meissner effect of polysulfur nitride, (SN)x

The magnetic susceptibility of (SN)_x was measured by the a.c. method. The Meissner effect occurs at 250 ± 3 mK. The real part of the susceptibility nearly saturates at 100 mK and reaches 93 ± 7% of ?$\text{1}\text{4}\text{π}$ at 30 mK for weak field perpendicular to the polymer axis, while for the parallel direction it remains at 65 ± 10% of ?$\text{1}\text{4}\text{π}$. The susceptibility depends strongly on the a.c. magnetic field. There is a peak in the imaginary part of the susceptibility at the transition region to the superconducting state.     

Hall to drift mobility ratio in Ga1−xAlxAs alloys

Hall concentration measurements as a function of temperature ($\text{750 ? T ? 77}\text{K}$) on n-type epitaxial layers of Ga_1?xAl_xAs in the composition range $\text{0 ? x ? 0.78}$, have been used to evaluate the composite dependence of the Hall to drift mobility ratio in this alloy at 300 K. This ratio is found to be close to unity for alloy compositions $\text{0 ? x ? 0.25}$ and $\text{0.6 ? x ? 0.78}$, but attains a maximum value of 3.8 at x = 0.42 due to the multiconduction Hall effect.     

The cooperative Jahn-Teller effect in uranium (4+) hydroxy-sulphate

The magnetic susceptibility measurements of orthorhombic U(OH)₂SO₄ within the temperature range 4.2–300 K have revealed a magnetic anomaly at T_D = 21 K associated with crystallographic transition induced by the cooperative Jahn-Teller effect. Above 21 K the magnetic susceptibility of the uranium (4+) ion corresponds to the electronic ground doublet ${}_{\mathrm{¡}}\text{M}{}_{\mathrm{J}}\text{= ± 2〉}$ confirming thus the antiprismatic symmetry (D_4d) of the crystal field at the uranium site. Below T_D the system of two singlets ($\text{1}\text{√2}$)|2〉 ± ($\text{1}\text{√2}$)|$\text{2}$〉 separated by δ(T) is the ground state of the uranium ion.     

Magnetization and exchange constants in Zn1−xMnxSe

Magnetization of Zn_1?xMn_xSe ($\text{x}\text{≤ 0.1}$) was measured for magnetic field up to $\text{B}\text{= 15}\text{T}$ in the temperature range 2.2 – 30 K. The obtained data were described by Brillouin-like function. The direct comparison of magnetization data with the previous magnetooptical data enabled us to determine the s-d exchange constants in $\text{Zn}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Mn}{}_{\mathrm{x}}\text{Se}\text{:}\text{N}{}_{\mathrm{<mtext>o</mtext>}}\text{α = 0.26}\text{eV}$, $\text{N}{}_{\mathrm{<mtext>o</mtext>}}\text{β = ?1.31}\text{eV}$.     

Evidence for exchange-coupled quadratic nets in CTS

Measurements of the low temperature heat capacity and powder magnetic susceptibility of CTS (Cu(NH₃)₄SO₄·H₂O) are shown to be consistent with quadratic nets of Heisenberg exchange-coupled spins ($\text{s =}\text{1}\text{2}$).     

Magnetic ordering of a d1 compound: VF4

Magnetic susceptibility and nuclear magnetic resonance above and below the ordering temperature show that VF₄ is an $\text{S =}\text{1}\text{2}$, 3d¹ canted antiferromagnet with a transition temperature near 28°K and a canting angle of ～ .02 rad. The compound is not an example of a proposed nonmagnetic singlet ground state of resonating covalent bonds.     

Superparamagnetic-like behaviour of magnetic alloys

The effect of antiferromagnetic interaction on a binary Ising ferromagnetic alloy A_pB_1?p is studied based on cluster-variational method and assuming either J_AB or J_BB or both exchange interactions to be of antiferromagnetic type. In a ferromagnetic state the moment saturates to a value much lower than its full value. Within the temperature interval where moment saturates, the system exhibits superparamagnetic-like behaviour. The induced moment becomes a function of $\text{h}\text{T}$ only, and the zero-field susceptibility follows Curie law. The incomplete saturation of moment persists up to a large value of $\text{h}\text{T}$. The short-range order parameter at T = 0 is much less than that of homogeneous ferromagnet.     

Magnetic structure of BaCaFe4O8-analysis of neutron diffraction measurements

The compound BaCaFe₄O₈ crystallizes in the trigonal space group P$\text{31}$m with one formula unit per unit cell with lattice constants $\text{a = 5.4059}\text{A}$ and $\text{c = 7.7023}\text{A}$ Neutron diffraction measurements carried out on a powder sample over the temperature range 300–900 K showed that the compound undergoes a magnetic transition to an antiferromagnetic state at a Néel temperature T_N = 680 ± 5 K. Analysis of the room temperature neutron diffraction pattern gave a magnetic unit cell that has the same periodicty as the crystallographic one. An antiferromagnetic model is proposed with the iron spin magnetic moments parallel to the c-axis of the unit cell. The magnetic moment of the Fe³⁺ ion was found to be (4.5 ± 0.1)μ_B