Nuclear magnetic resonance of orientedMn54nuclei in antiferromagnetic MnCl

Abstract

NMR of oriented Mn in antiferromagnetic MnC12 4H20 has been studied by monitoring the change in y-ray intensity. The strongest line has frequency 500.4+0.1 MHz and weaker lines are observed at 503.5+0.1 and 507.0+0.5 MHz. The linewidth is 35+5 kHz. A value for the hyperfine interaction strength A = -203.8+0. 1 MHz is deduced. The 3.1-MHz splitting of the lines is due to second-order magnetic "pseudoquadrupole" interaction (2.7 MHz) and pure quadrupole interaction (0.4 MHz). Point-charge calculations agree fairly well with the latter value.

In situ 54Mn NMRON Studies of the Mixed Halide Mn(Br X Cl1−X )2 · 4H2O in Applied Magnetic Fields

“…It was not observable in the higher temperature runs with the 19.4 mCi (see Figure 1(a)). It is sufficiently low in frequency that it is not readily identified with calculations based on molecular field theory [3,7]. Finally, in Figure 4 we compare the applied field dependence of the genuine NMRON signals (three lines in all) with the ªj3> to ªj2> NMRON of the terminal compounds.…”

“…More recently MnCl 2I 4H 2 O has been used as a LTNO host for on-line implantation [4]. Rather surprisingly, despite being monoclinic, with four Mn ions per unit cell and measurable biaxial anisotropy, MnCl 2 I 4H 2 O behaves like a simple uniaxial two sub-lattice antiferromagnet (AF), with a well-defined single stage spinYflop B SF and paramagnetic transition B P [3,5,6]. This is in marked contrast with the nominally isomorphic compound MnBr 2 I 4H 2 O (T N = 2.12 K), which is characterised by a two-stage spinYflop [7].…”

Nuclear orientation of radioactive56Mnions implanted in the insulatorsMnCl2

“…The 2ϩ Mn ion has a half-filled 3d shell and ''spin only'' magnetism, but there are crystal-field effects that reduce the hyperfine field from that expected for the free ion value. 5 Therefore, it is likely that the hyperfine interaction for nonsubstitutional Mn ions will be different from, but possibly close to, the full value. The observed anisotropy might be due to a majority of implanted ions in substitutional sites feeling the full hyperfine field and a few experiencing zero effect ͑two-site model͒ or to many ions having a field slightly different from the full value.…”

“…The magnetic properties have been studied by NO and NMRON using 54 Mn as the radioactive probe. [4][5][6][7] In fact, it was the first insulating ordered magnet in which NMRON was successfully performed. 4 CoCl 2 •6H 2 O is also antiferromagnetic with a similar crystallographic structure, but with ␤ϭ122.3°, and an ordering temperature of 2.3 K. The easy axis of magnetization is the c axis.…”

Spin Flop Studies in the AF Mixed Halide (54Mn)Mn(Br x Cl1−x )24H2O via Low Temperature Nuclear Orientation

“…The terminal compound MnCl 2 I 4H 2 O (T N = 1.62 K) has been widely studied at and around 3 He temperatures and its magnetic unit cell is well determined. Subsequently, it was also the first AF insulator to be resonated in a nuclear magnetic resonance on oriented nuclei (NMRON) environment using in situ gamma anisotropy from 54 Mn probes [2]. A comprehensive low temperature nuclear orientation (LTNO) and NMRON study was undertaken by [3] who showed that a magnon energy gap bottleneck was the primary cause for the severely limited LTNO, which occurred even for very weakly doped samples, but could be defeated by applying magnetic fields at or just below the spin flop field of B SF õ 0.7 T. By exploiting very large g-anisotropies obtained via this novel magnon heat switch they were able to show in detail [3] that the spin flop transition was single stage, notwithstanding four Mn ions per unit cell with the Cl's in low symmetry cis geometry, and continuous, with no observable hysteresis for field sweeps in opposite directions; that is, second order in character.…”