High External Magnetic Field Research Articles

Spin-lattice relaxation in erbium ethylsulphate

Data are presented on the paramagnetic spin-lattice relaxation times in concentrated erbium ethylsulphate. The results, above 4 K, can be described by means of an Orbach process: (τ L) H c = 0.5 kOe = 1.55 × 10 −10 exp( 54 T ) s. In a single crystal with H c ⊥ c axis double relaxation processes have been observed at the temperature of liquid helium at external magnetic fields above 3 kOe. This behaviour is studied extensively on several samples. It is noticed that the double relaxations become less pronounced if the crystal size decreases and this suggests the double relaxation behaviour is related to phonon bottleneck effects. The relaxation time in the powdered sample, at low temperatures and high external magnetic fields, is found to be proportional to T -1.8 H c -1.8; this may indicate that relaxation dependences have been observed intermediate between that of an Orbach process and that of a direct process. The b/ C value is found to be 9.7 x 10 4 Oe 2 if H c ⊥ c axis and 1.5 x 10 6 Oe 2 if H c c axis.

Mössbauer Effect in 57Fe in Copper and the Spin-Compensated State

The results of Mössbauer experiments on dilute Fe in Cu in high external magnetic fields (42–146 kOe) are presented here as evidence for significant destruction of the spin-compensated state by a magnetic field for which μH0∼kTK, where kTK is on the order of the energy change associated with the formation of the spin-compensated state.

MÖSSBAUER Evidence for a Spin-Compensated State in Dilute Fe-Cu Alloys

There has been considerable recent interest in the existence and nature of the bound statel 9 which is thought to be formed in certain dilute alloys between localized magnetic impurity moments and conduction-electron spins below some critical temperature characteristic of the alloy. In their recent communication, Day­ bell and SteyertlO presented evidence based on low-temperature resistivity and suscepti­ bility measurements for the formation of such a bound state consistent with some quenching of the localized moment·associated with very dilute Fe in Cu. The results of Mossbauer ex­ periments on dilute Fe in Cu in high external magnetic fields (42-136 kOe) are presented here as evidence for significant destruction of the bound state by magnetic fields for which J1H 0 ''J k TK where k T K is on the order of the energy change associated with the formation of the bound state. The fact that the Mossbau­ er hyperfine .spectrum reflects the electronic environment within atomic dimensions of the 57Fe nucleus enables us to make some conjec­ tures as to the singlet nature of the bound state. The hyperfine interaction in dilute Fe in eu al­ loys has been reported by Kitchens, Steyert, and Taylor!! using the M<1ssbauer technique in exter­ nal magnetic fields up to 62 kOe and at temper­ atures down to 0.4°K. They noted significant deviations from pure paramagnetic behavior and interpreted their results in terms of a mod­ el due to Housley and Dash,!2 who introduced a phenomenological interaction between the localized Fe spin and conduction-electron spin­ density waves. Measurements at higher fields (Ho=110 kOe) were reported by Blum, Free­ man, and Grodzins.1s In the ideal paramagnet­ ic case the hyperfine field Hhf is proportion­ al to a Brillouin function characterized by the parameters J, g, and H sat 14:

Mössbauer Studies of Spin Flop in Antiferromagnetic Hematite

The antiferromagnetic sublattice magnetizations below the Morin transition temperature TM≈260°K, are parallel and antiparallel to the trigonal axis of rhombohedral α-Fe2O3. Experiments at 80°K, using the Mössbauer technique together with high external magnetic fields on both polycrystalline and single-crystal samples, show that the directions of the sublattice magnetizations flop from along the trigonal axis for the applied field H0&amp;lt;Hc to perpendicular to the trigonal axis for H0&amp;gt;Hc; Hc is found to be 67.5±3 kOe. In the polycrystalline sample this behavior is exhibited through the occurrence of a maximum in the width of the outer lines of the Mössbauer spectrum plotted as a function of H0. In the single crystal, which is oriented so that the gamma rays propagate along the [111] direction, the magnetic transition is clearly observed as a sudden qualitative as well as quantitative change in the appearance of the Mössbauer hyperfine spectrum; below the critical field the Δm=0 lines are the strongest components of the six-line spectrum.

Magnetic Deflector for Mesons Produced in the 184-Inch Cyclotron

A magnetic deflector has been constructed which makes the mesons artificially produced in the 184-inch cyclotron by alpha-particle bombardment available outside the cyclotron tank. The deflector consists of a magnetic shield especially designed to operate in very high external magnetic fields. The effect of the magnetic shield on the internal cyclotron beam has been compensated by pole shims. The deflector yields a total meson flux of approximately 500 mesons per minute.