摘要:

We report here on the magnetic properties of compounds of composition Fe1−xCrxSbO4and Fe1−xGaxSbO4. The introduction of paramagnetic Cr3+and diamagnetic Ga3+into the rutile‐related iron antimonate lattice does not destroy the antisite atomic ordering which exists in iron antimonate of composition FeSbO4. The initial slope of the Curie temperature dependence onxis similar in both series, indicating that Fe3+‐Cr3+interactions are very small. The magnetic susceptibility measurements recorded from the compounds of composition Fe1−xCrxSbO4,x<0.4, and Fe0.9Ga0.1SbO4show them to behave as spin glasses at low temperatures. The inhibition of compounds of the type Fe1−xCrxSbO4,x>0.4, and Fe1−xGaxSbO4,x>0.1 to undergo a spin‐glass transition above 4.2 K is associated with a dilution effect.

ISSN:0021-8979    

DOI:10.1063/1.341125

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Magnetization‐versus‐temperature (M‐vs‐T) measurements in a fixed field on cubic pseudobinary Tb0.3Y0.7Ag show thatMfor increasing and then decreasingTbifurcates at the antiferromagnetic Ne´el point (TN=36 K), whereMis maximum. The resulting thermoremanence (MR), which decays very slowly with time, diminishes with increasingTand vanishes atTN. Thus, the long‐range antiferromagnetism appears to coexist with spin‐glass ordering. Measurements ofMRwith increasingTwere also made for different cooling fields (Hc1) The changes ofMRwithHclandTare found to reduce to a universal relationship between the temperature‐normalized quantities,m=MR/M0(T) andh=Hcl/H0(T). Setting both the initial slope ofmvshand the saturationmat highhequal to unity, we determine thatM0(T)=M0(0) exp (−T/T0), withM0(0)=0.82&mgr;B/Tb atom andT0=4.3 K, and thatH0(T) varies analogously, withH0(0)=225 kOe and the sameT0. A similar temperature scaling ofMRvsHcl, with similar exponential forms forM0(T) andH0(T), has been deduced earlier for Ag‐Mn and other canonical spin glasses.

ISSN:0021-8979    

DOI:10.1063/1.340194

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Nonstationary dynamics has been observed in very‐low‐frequency (10−2–10−1Hz) ac susceptibility and noise measurements on the thiospinel CdCr1.7In0.3S4spin glass. The time relaxation of the ac susceptibility yields a large decrease of the out‐of‐phase component &khgr;‘towards a finite stationary value. The relaxation of the spectral density of the magnetization derived from zero‐field noise measurements is in remarkable agreement with the behavior of &khgr;‘. The observed time dependence compares well with the predictions from the thermoremanent magnetization decay analyses. In the range of times of &khgr;‘measurements, the linear‐response theory applies to the nonstationary dynamics.

ISSN:0021-8979    

DOI:10.1063/1.340169

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Magnetization‐vector measurements were made on a slowly rotating disk sample of Au85Fe15after cooling to 4.2 K from aboveTg(=52 K) in a 15‐kOe field that saturates the thermoremanence. ForMT, the magnetization component transverse to the applied fieldH, results are shown asHMTvs &thgr;, the sample‐rotation angle relative toH, for &thgr; cycled between 0° and 180° at each value ofH. ForH≲0.1 kOe,HMTvaries nearly reversibly in simple accord with an anisotropy fieldHK(0.41 kOe in size) that rotates rigidly with the sample. At higherH, the rotational hysteresis grows rapidly until, forH≳0.4 kOe, another simple but highly irreversible behavior is observed. From this behavior, it is deduced thatHKrotates relative to the sample isothermally when the torque on it exerted by the sample magnetization reaches the magnitude of a frictional torque. The frictional‐torque coefficient is seen to decrease steadily with increasingH, as confirmed by direct measurements of the rotations of the remanence that result from sample rotations in variousHat 4.2 K.

ISSN:0021-8979    

DOI:10.1063/1.340170

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Torque relaxation data on a Cu 5‐at. % Mn sample at different temperatures are presented. The relaxations after field cooling and after zero‐field cooling are different at each temperature, implying that the in‐field states of the sample after these two procedures are different. Torque data for the effective anisotropyKare compared with values from experiments having shorter time windows so as to obtain information on relaxation over a very wide time spectrum. The estimated effectiveTgvalues tend to a frequency‐independent limit at low frequencies.

ISSN:0021-8979    

DOI:10.1063/1.340171

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Zero‐field muon‐spin‐relaxation (&mgr;SR) andX‐band ESR have been used to study the spin‐freezing dynamics in single crystals of the Ising spin glass Fe2−xTi1+xO5. Parameters obtained for the power‐law and Vogel–Fulcher descriptions of the critical slowing are consistent with other methods forx=0 and indicate significantly slower freezing in Ti‐rich samples. Interpretation of cluster effects, observed inx=0.25‐&mgr;SR data, as a Griffiths‐like phase yields an estimate of 61±1 K for the Ne´el temperature in site‐ordered Fe2TiO5.

ISSN:0021-8979    

DOI:10.1063/1.341145

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Using magnetic resonance data at several frequencies, we have obtained the temperature dependence of the field‐induced magnetization (M) in three concentrated spin glasses. At every frequency,Mis independent ofTforT≲TSGand drops linearly withTat higher temperatures. [M(0)−M(T)]/M(0) is closely represented by the function [exp(&Dgr;/T)−1]−1, where &Dgr; is a characteristic gap energy with values close to the corresponding Curie–Weiss temperatures &thgr;pbut much larger than the respective spin‐glass transition temperaturesTSG.

ISSN:0021-8979    

DOI:10.1063/1.340172

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The pseudo‐one‐dimensional mixed system [(CH3)3NH]Co1−xNixCl32H2O was found to exhibit spin‐glass behavior below a characteristic temperature evidenced by the onset of time‐dependent thermoremanent magnetization. In order to confirm the spin‐glass behavior we now have studied the ac susceptibility of this series in zero field using an ac SQUID susceptometer. Along the weak ferromagnetic axis (aaxis), the ac susceptibility shows a cusp at the spin‐glass transition temperature. Increasing the measurement frequency from 80 to 160 Hz increases the slope of the susceptibility below the transition temperature but no significant shift in the transition temperature itself is seen for this small frequency range. Spin‐glass behavior is seen only along theaaxis and a typical antiferromagnetic transition is seen along thecaxis.

ISSN:0021-8979    

DOI:10.1063/1.340174

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have studied the magnetization in the spin‐glass phase ofAgMn under the repetitive application of a small (10 Oe≤h≤50 Oe) magnetic field [asymmetric hysteresis cycles (L. Ne´el, in Proceedings of the R. A. Welch Foundation Conference on Chemical Res. II, Atomic Structure, Houston, Texas, 1958)] after the sample has been cooled in a static fieldH(0≤H≤1.1 kOe). WhenH=0, the magnetizationmnin the field off state (h=0) grows as the logarithm of the number of cycles (n), while the magnetization in the on state (h≠0)Mndecreaseswith cycle number. This weaker response reflects an increase of the stiffness of the spin system after each cycle. At low temperaturemngrows linearly with temperature, reaches a maximum aroundT∼0.6Tgand decreases asTgis approached. The effects are larger when the system is prepared in a nonequilibrium state (rapid thermal quenching, or removal of the static fieldH). The irreversible growth of the magnetizationmnscale linearly withTg(i.e., exchange) for samples of 0.5 and 2.6 at. % Mn concentration. We find thatmngrows as the value ofHis increased, reaches a maximum aroundH∼Tg/15 and decreases slowly at higher fields. We suggest as a possible interpretation of this phenomenon, the existence of a cavity in the distribution of local fields acting on the low temperature excitations. Additional information on the role of anisotropic forces will also be presented.

ISSN:0021-8979    

DOI:10.1063/1.340175

出版商:AIP    

年代:1988

数据来源: AIP