External Magnetic Field Measurements Research Articles

Mössbauer study of the amorphous alloy Zr 100− xFe x

The hyperfine field distributions were determined from Mössbauer spectra of Fe 91Zr 9 taken for 6 K < T < 230 K. As in other alloys with invar behaviour, the distribution consists of a high field peak and a broad low field tail. Measurements in external magnetic fields show the ferromagnetic nature of the spin coupling. No evidence was found of an antiferromagnetic component at low fields. For Zr-rich alloys, the distribution of quadrupole splitting was evaluated from the spectra and compared with that found for metastable crystalline alloys. The differences between the two distributions suggest that important changes occur in the short-range order on crystallization.

Experimental and Theoretical Study of the Phase Diagram of the Linear Antiferromagnet (CH3)4NMnCl3 (TMMC)

Magnetic phase diagrams of the most typical quasi-one-dimensional antiferromagnet (CH 3 ) 4 NMnCl 3 ( T N =0.835 K) reported in our previous paper have been investigated in more detail by heat capacity and magnetic susceptibility measurements in external magnetic fields up to 30 kOe. The phase diagrams for the external field applied along the in-plane easy and hard axes normal to the magnetic chain are reproduced satisfactorily by the theory in which the classical anisotropic XY model is assumed for the magnetic chain and interchain interarctions are treated within the molecular field approximation. The magnitude of the anisotropy field in the plane normal to the chain is determined to be 93 Oe.

On rf-magnetoresistance and flux flow resistivity of NbTi

The temperature and magnetic field dependences of the surface impedance of Nb50 wt/oTi were investigated with a TE 011-mode cavity operated at a frequency of 9.67 GHz. The results with the cavity cooled down in the earth's magnetic field show good agreement with the BCS-behaviour of the surface resistance in the Meissner state when a reduced gap, Δ(O) k BT c of 1.97, and a mean free path of 0.5 nm are assumed. Measurements in external magnetic fields up to 3 T were used to obtain the flux flow resistivity (FFR) of NbTi. The FFR obtained in this way shows a marked deviation from the phenomenological straight line behaviour ρ 1 ρ n = B H ∗ c 2 , which has been found all low- and medium-K superconductors. This indicates that the high K of NbTi leads to reduced flux flow losses at lower magnetic fields in qualitative agreement with calculations by Hu and Thompson for gapless high-K superconductors. Investigations of the temperature dependence of the ffr resulted in a resistance minimum being deeper and occurring at higher temperatures than those which have been reported for all other materials investigated to date.

Antiferromagnetism of FCC Fe thin films

Thin iron films (∼18 Å thick and 90% enriched in 57Fe) were prepared on (001) Cu single crystal substrates. By using Mössbauer spectroscopy it was found that antiferromagnetic ordering begins at around 80 K ± 10 K with average hyperfine fields of about 14–20 kOe at 4.2 K. Additional proof for the existence of antiferromagnetism has been obtained by measurements in a longitudinal external magnetic field. The apparent discrepancy in the literature of ferro- and antiferromagnetic ordering in fcc Fe films is discussed.

Magnetic properties of single-crystal β-phase iron-germanium

Mössbauer effect measurements in external magnetic fields up to 50 kOe indicate Fe 5Ge 3 has a collinear magnetic structure. A large anisotropy in the hyperfine magnetic field has been found.

Low temperature thermal expansion and magnetostriction of TmCd

Thermal expansion measurements in various external magnetic fields confirm the recently found Jahn-Teller transition in TmCd at 3.16 K. The tetragonal strain ϵ 3 at T = 0 K is found to be 0.62 × 10 −3. From magnetostriction data we determine a coupling constant g 0 2 = 0.4 × 10 −3 K which is in good agreement with the value found from ultrasonic experiments. In order to explain our magnetostriction results in the cubic phase, g 0 has to be taken negative.

Magnetic Properties of FeCl2·2H2O

The magnetic properties of Fe${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O have been investigated by means of single-crystal magnetic susceptibility, high-field magnetization, and proton nuclear-magnetic-resonance (nmr) measurements. A transition to an antiferromagnetic state is observed at ${T}_{N}\ensuremath{\approx}23\ifmmode^\circ\else\textdegree\fi{}$K. The magnetic susceptibility tensor in the paramagnetic state has uniaxial symmetry about an axis ($\ensuremath{\alpha}$) lying in the ac plane ($\ensuremath{\alpha}={\ensuremath{\alpha}}^{*}+58\ifmmode^\circ\else\textdegree\fi{}$). In the range 30-100\ifmmode^\circ\else\textdegree\fi{}K the measured susceptibilities follow a Curie-Weiss relation with ${g}_{\ensuremath{\alpha}}=2.4$, ${g}_{\ensuremath{\beta}}\ensuremath{\approx}{g}_{\ensuremath{\gamma}}=1.9$, and effective Weiss constants ${\ensuremath{\Delta}}_{\ensuremath{\alpha}}=12\ifmmode^\circ\else\textdegree\fi{}$K, ${\ensuremath{\Delta}}_{\ensuremath{\beta}}\ensuremath{\approx}{\ensuremath{\Delta}}_{\ensuremath{\gamma}}=5\ifmmode^\circ\else\textdegree\fi{}$K. The zero-field proton nmr in the ordered state consists of a single spin-spin doublet with extrapolated center frequency at 0\ifmmode^\circ\else\textdegree\fi{}K ${\ensuremath{\nu}}_{0}=9.231\ifmmode\pm\else\textpm\fi{}0.001$ Mc/sec. Proton nmr measurements in weak external magnetic fields at 4.0\ifmmode^\circ\else\textdegree\fi{}K give four symmetry-related proton local-field directions. The magnetic susceptibility and proton nmr experiments give evidence for a magnetic structure ($\frac{\mathrm{Pc}2}{m}$) in which ferromagnetic chains, parallel to the $c$ axis, are coupled antiferromagnetically to adjacent chains. The direction of sublattice magnetization coincides with the $\ensuremath{\alpha}$ axis. The magnetization behavior at 4.0\ifmmode^\circ\else\textdegree\fi{}K and with $\mathrm{H}\ensuremath{\parallel}\ensuremath{\alpha}$ exhibits two metamagnetic transitions, ${H}_{c1}=39\ifmmode\pm\else\textpm\fi{}1$ kOe and ${H}_{c2}=46\ifmmode\pm\else\textpm\fi{}1$ kOe. The corresponding magnetic moments are ${M}_{1}=1.4\ifmmode\pm\else\textpm\fi{}0.1{\ensuremath{\mu}}_{B}$ and ${M}_{2}=4.25\ifmmode\pm\else\textpm\fi{}0.05{\ensuremath{\mu}}_{B}$. The first magnetization discontinuity is shown to result from an antiferromagnetic intrasublattice interaction which makes the two-sublattice zero-field configuration unstable with respect to a six-sublattice modification in sufficiently strong external fields.

Attenuation of longitudinal ultrasonic waves in aluminium at low temperatures

The attenuation of longitudinal sound waves has been measured in two very pure aluminium single crystals down to 0.4°K at frequencies between 5 and 35 MHz. As would be expected, no dependence on crystal orientation has been found. The ratio between the attenuations in the superconductive and the normal state proved to be slightly frequency-dependent. The results are compared with theory. Measurements in external magnetic fields have also been carried out.