Spin-flop Field Research Articles

Nuclear Magnetic Resonance in Antiferromagnetic Cu2P2O7

The 31P nuclear magnetic resonance has been studied for the antiferromagnetic state of Cu2P2O7. The external field was smaller but in many cases comparable to the spin flop field. It was necessary to correct for the perturbation of the spin system by the applied magnetic field. The data are compared with the spin configuration determined by neutron diffraction, the transferred hyperfine interaction measured in the paramagnetic state, and the magnitude of distortions from a higher symmetry phase.

Magnetic measurements on (CH 3NH 3) 2MnCl 4, a quasi two-dimensional Heisenberg antiferromagnet

We have measured the magnetic susceptibility of the first member of a series of tetragonal compounds of general formula (C n H 2 n+1 NH 3) 2MnCl 4 ( n = 1,2,3,…), which may be considered to consist of nearly isolated antiferromagnetic layers. The interlayer coupling J′ is estimated to be 10 −9-10 −8 of the intralayer exchange J, a result 10 2 smaller than may be realized within the well-known K 2NiF 4 structure. Quantitatively, we obtain J/ k = −5.0 ± 0.2 K for the intralayer exchange and H A / H E = 1.1 × 10 −3 for the anisotropy, the latter being derived from the spin flop field.

Spectroscopic study of Er3+-Gd3+interaction in Er:GdAlO3

Zeeman optical absorption spectra of Er:GdAlO3 have allowed a determination of the principal values of the Er3+-Gd3+ exchange interaction for the ground state and the lowest components of 4S3/2 and 4F9/2 states of Er3+. Using these interaction data, the highly nonlinear behaviour of the low field Zeeman spectra (H<40 kG) can be explained satisfactorily for the highest energy lines, which can be assigned unambiguously. Qualitative evidence for canting of Gd3+ moments which are NN to Er3+ ions is discussed, and a study of the angular dependence of the spin flop field provides evidence that the Gd3+ moments flop into the bc rather than the ab plane.

Critical behaviour of the perpendicular susceptibility of antiferromagnetic (C 2H 5NH 3) 2 CuCl 4

The perpendicular susceptibility of antiferromagnetic (C 2H 5NH 3) 2 CuCl 4, measured as a function of a magnetic field, displays anomalous behaviour near to the transition to the paramagnetic phase. The observed effects have been qualitatively predicted by spin wave theory. The temperature dependence of the latent heat of transition at the spin flop field H 1 has also been obtained. It is discussed that for this salt the sign of d H 1/d T is negative.

Ultrasonic Attenuation andMn55Nuclear Acoustic Resonance in MnTe

The ultrasonic attenuation in MnTe for longitudinal waves with propagation vector in the hexagonal plane was measured as a function of temperature for frequencies up to 530 MHz. The attenuation below the N\'eel temperature comprises both background losses and an extraordinarily intense (attenuation up to 300 dB/cm) temperature-dependent resonance absorption caused by ${\mathrm{Mn}}^{55}$ nuclear acoustic resonance. Extrapolation to zero temperature yields a resonance frequency ${f}_{\mathrm{NAR}}=466.5$ MHz and a hyperfine field ${H}_{n}=442$ kOe. Theoretical expressions for the sound absorption due to electronic and nuclear spins were derived. Comparison with the measured magnetic-field dependence of background and nuclear-acoustic-resonance (NAR) absorption suggests that spins located in domains rather than inside domain walls are mainly responsible for the observed effects. The spin-flop fields, observed in the NAR experiments, are much higher than the values calculated from anisotropy constants and susceptibilities. Good agreement between experiments and theory is obtained for $H\ensuremath{\gg}{H}_{\mathrm{S}\mathrm{}\mathrm{F}}$.

Magnetic Phase Diagram of Hexagonal FeGe

The magnetic phase diagram (B-T phase) of hexagonal FeGe was determined by measurements of the differential magnetic moment dM/dB. In an external pulsed magnetic field parallel to the magnetic axis (c-axis) spin flop transitions were observed for temperatures from 1.5 K to 290 K. The critical spin flop field at 4.2 K is 7.1 T (71 kG).

The effect of anisotropy on the critical temperature of two-dimensional heisenberg antiferomagnets

The anisotropy derived from the spin flop field, is 4 times larger for Rb 2NiF 4 than for K 2NiF 4. The effect of this difference in H A H E on T N, expressed as kT N J , is only small: i.e. 17 ± 5%.

Magnetic phase diagram of Cs 3Cu 2Cl 7.2H 2O

The magnetic phase boundaries of Cs 3Cu 2Cl 7.2H 2O, with Néel point 1.625°K, have been determined in external fields up to 56 kOe. The temperature dependence of the spin flop field is described by the equation H c(kOe) = 5.50 + 0.27 sinh 1.19 T.

Nuclear magnetic resonance and magnetic structure of antiferromagnetic Mn2P2O7

The nuclear magnetic resonance of 31P in antiferromagnetic Mn2P2O7 has been investigated at constant r.f. frequencies with the external field smaller than the spin-flop field. Resonance measurements were made in a single crystal sample at liquid helium temperatures. Experimental data, including the angular dependence, the external field dependence, and the temperature dependence of the resonances, are satisfactorily explained by the spin Hamiltonian formalism for NMR in antiferromagnets, proposed by the authors. NMR results confirm the spin direction obtained from susceptibility measurements, and establish the magnetic space group as C2c2.

Low temperature magnetic heating in single crystal NiO

Abstract We have observed a latent heat associated with the spin flop phenomena in a NiO single crystal at 2°K. This measurement shows the spin flop field to be less than 600 oe and the inplane anisotropy field to be approximately 0.1 oe.

Spin-flopping in CsMnCl3 · 2H2O

The magnetization of CsMnCl3·2H2O has been measured up to 22.5 kOe. The spin-flop field Hc and the direction of the flopped spins has been determined.

Theoretical Studies of an Absorption Spectrum of an Antiferromagnetic Rare-Earth Garnet, Dy3Al5O12

Crystal field calculations have been performed on the 6 F 3/2 , 6 F 5/2 , 6 F 7/2 , 6 H 5/2 and 6 H 15/2 states of the Dy 3+ ion in the paramagnetic state. The optical absorption spectra for the transition 6 H 15/2 → 6 F 5/2 have also been studied in detail. The results indicate that the signs of some of the crystal field parameters V n m based on a point charge calculation have to be changed in order to reproduce the observed level positions and g values of the 6 F 5/2 state. Such change of the crystal field parameters may be ascribed to large shielding of the crystal field potential. The selection rules derived in the present paper are consistent with the ones obtained in the preceding paper. The theoretical selection rules have been applied successfully to the splittings of the 6 F 5/2 and 6 H 15/2 states below the Neel temperature by using the molecular field approximation. The magnetic-field effect on the absorption lines below the spin-flop field has also been discussed.

Temperature Dependence of the Antiferromagnetic Resonance Linewidth in EuTe

The linewidth of EuTe has been measured as a function of temperature through and above the Néel temperature. The samples used were single-crystal spheres, the magnetic field lying in a (111) plane along a 〈112̄〉 direction. EuTe is an easy-plane antiferromagnet having an in-plane spin-flop field of 700 G. These measurements at 24 GHz and about 8½ kG were for the low-frequency branch in the spin-flopped condition. The temperature dependence of the linewidth is similar to results obtained on other antiferromagnets. The linewidth rises from 150 G at 0.1 TN to a sharp maximum of 2700 G near, but slightly above TN, dropping to 1000 G at 2.0 TN. The results in the paramagnetic region have been compared with the [T/(T−TN)]¾ dependence predicted by Mori and dependence predicted by Mori and Kawasaki. Fitting this expression to the measured linewidth at 77°K gives good agreement down to 12°K (TN=9.6°K). For the antiferromagnetic region, the linewidth decreases approximately linearly with temperature and is not explained by existing theories.

Magnetic Properties of Antiferromagnetic GdAlO3

Specific-heat and magnetic-susceptibility measurements on GdAlO3 show that it undergoes a transition to antiferromagnetism at 3.69°K. Magnetization measurements on a single crystal at temperatures down to 0.6°K in fields up to 70 kOe show that the ordered state is a simple two-sublattice structure with the orthorhombic b axis as the axis of alignment. The spin flop, exchange, and anisotropy fields have been found to be 11.2 kOe, 20 kOe to 25 kOe, and 2.3 kOe to 3.0 kOe, respectively. No parasitic ferromagnetism is observed. Optical absorption studies of Er3+ and Dy3+ in GdAlO3 observe the spin flop and confirm that in the ordered structure the distorted simple cubic lattice of Gd3+ ions divides into two sublattices with each ion surrounded by six nearest neighbors belonging to the opposite sublattice.

High-Field Antiferromagnetic Resonance inCr2O3

Antiferromagnetic resonance (AFMR) experiments in single-crystal ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ are summarized with specific emphasis on the high-field resonance mode. Most of the experiments involve pulsed magnetic fields and millimeter wavelength radiation. A brief description of the experimental techniques is included. The experimental results include AFMR as a function of temperature (from 4.2\ifmmode^\circ\else\textdegree\fi{}K to the N\'eel temperature), frequency (36 to 135 kMc/sec), magnetic field, and angle between the magnetic field and the $c$ axis. Results of the spinflop resonance mode are also presented as a function of temperature, field, frequency, and angle. Magnetic measurements at the spin-flop field and low-field static susceptibility measurement both parallel and perpendicular to the $c$ axis are also given as a function of temperature. Normalized plots of the AFMR based on the molecular field approximation are presented as a function of angle and field and compared with experiment. The AFMR experiments agreed with the molecular field results when the static susceptibility data were included in the calculations. The characteristic quantity ${(2{H}_{E}{H}_{A})}^{\frac{1}{2}}$, where ${H}_{E}$ is the exchange field and ${H}_{A}$ is the anisotropy field, is 60\ifmmode\pm\else\textpm\fi{}3 kG from 4.2 to 235\ifmmode^\circ\else\textdegree\fi{}K. The unusual temperature independence of ${(2{H}_{E}{H}_{A})}^{\frac{1}{2}}$ is partly accounted for by the crystalline field contribution to ${H}_{A}$ which is only 700 G at 4.2\ifmmode^\circ\else\textdegree\fi{}K. Assuming only dipolar and crystalline field contributions to ${H}_{A}$ the crystalline field portion at low temperatures is 1000 G. This corresponds to an axial $D$ contribution which is 1/9 that of ${\mathrm{Cr}}^{3+}$ in ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and of the opposite sign. More recent optical and related data which confirm this result are discussed and some possible mechanisms of the unusual temperature dependence are indicated. A nonzero value of the parallel static susceptibility at low fields is also observed and briefly discussed.

Magnetoelectric Effects in Cr2O3 and (Cr2O3)0.8· (Al2O3)0.2

Magnetic field induced magnetoelectric (ME) effects in Cr2O3 and (Cr2O3)0.8·(Al2O3)0.2 have been examined with an ac method as a function of temperature and magnetic field. The ME effect parallel to the c axis reverses in sign at low temperatures for both materials, and is linear in H for all temperatures up to the spin-flop field HC after which the ME effect approaches zero. The temperature dependence of the extrema of (dE/dH) vs H leads to a measure of HC vs T which agrees with earlier antiferromagnetic resonance and magnetic moment data in similar materials. Complete reversibility of the ME effect is observed when the magnetic field exceeds HC and then returns to lower values, thus demonstrating a stable memory of the domain distribution introduced during magnetic annealing. Brief remarks are made on the angular dependence of the ME effect, and indications of nondiagonal contributions in the vicinity of HC are mentioned.